Development of glacial hazard and risk minimisation ... · Development of glacial hazard and risk minimisation protocols in rural environments Methods of glacial hazard assessment

Development of glacial hazard and risk minimisation protocols in rural environments Methods of glacial hazard assessment and management in the Cordillera Blanca, Peru

April 2003 Project No: R7816.H

Reynolds Geo-Sciences Ltd2 Long Barn, Pistyll Farm

Nercwys, MoldFlintshire, CH7 4EW, UK

Tel: +44 (0)1352-756196Fax: +44 (0)1352-759353

E-mail: [email protected]: www.geologyuk.com

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April 2003 Issue 1.0

Notice:

The intellectual property rights represented by the documents contained herein are vested in Reynolds Geo-Sciences Ltd and are protected under UK law. The use of the technical detail by third parties without the express permission of Reynolds Geo-Sciences Ltd and without due recompense is not permitted under any circumstances.

The copyright of the document herein belongs to Reynolds Geo-Sciences Ltd and all rights are protected.

© Reynolds Geo-Sciences Ltd, March 2003, all rights reserved.

This document is an output from a project funded by the UK Department for International Development

(DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.

Cover picture:

Rapidly disintegrating tongue of Llaca Glacier, Cordillera Blanca Peru.

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Methods of glacial hazard assessment and management in the Cordillera Blanca, Peru

CONTENTS: 1 INTRODUCTION............................................... 1 1.1 Terms of Reference ................................. 1

1.2 Aims and objectives ................................ 1 2 THE MANAGEMENT OF GLACIER- RELATED RISKS IN THE PERUVIAN CORDILLERAS ................................................ 3 2.1 Introduction.............................................. 3

2.2 Deglaciation and hazard formation in Peru .......................................................... 3 2.3 The management of glacial hazards in Peru ........................................................... 5

2.4 Remediation of glacial lakes .................. 5

3 RAUCOLTA GLACIER................................... 11

3.1 Introduction............................................ 11

3.2 Theories of lake development .............. 11

3.3 Historical development of Raucolta Glacier ............................................................ 12

3.4 Field observations ................................. 13

3.4.1 Glaciological setting ........................ 13 3.4.2 Structure of Raucolta Glacier.......... 13 3.4.3 Ablation of Raucolta Glacier ........... 16 3.4.4 Hydrology of Raucolta Glacier........ 16

3.5 Interpretation.......................................... 16

3.6 Implications for glacial hazard evaluation............................................... 17

3.6.1 Potential for lake development ....... 17 3.6.2 Glacier surface gradient as an indicator of lake development potential ............................................ 18

3.7 Recommendations ................................. 18

3.8 Conclusions ........................................... 18

4 LAGUNAS SAFUNA ALTA AND SAFUNA BAJA .............................................. 20

4.1 Introduction ............................................ 20

4.2 The setting of the Safuna lakes ............ 20

4.3 The geological setting of the Safuna lakes ........................................... 20

4.4 Recent history of the Safuna lakes ...... 21

4.5 Lake remedial measures ....................... 22


4.6.1 Bathymetric and topographic surveys......................... 23 4.6.2 Moraine dam ...................................... 23 4.6.2.1 Lateral moraines ......................... 23 4.6.2.2 Terminal moraine ........................ 24 4.6.2.3 Moraine stability .......................... 25 4.6.3 The tunnels ........................................ 26 4.6.4 Rock slopes ....................................... 26 4.6.5 Safuna Glacier ................................... 28 4.6.6 Hydrology .......................................... 29

4.7 The landslide of 22nd April 2002............ 29

4.7.1 Summary of the April 2002 event .... 29 4.7.2 Lake and seiche waves .................... 30 4.7.3 Moraine and tunnels ......................... 30 4.7.4 Lower lake ......................................... 32

4.8 Hazard assessment................................ 33

4.8.1 Moraine Dam ..................................... 33 4.8.2 Trigger mechanisms......................... 35

4.9 Potential vulnerability............................ 36

4.9.1 Tourism and Visitors ........................ 36 4.9.2 Habitation........................................... 36 4.9.3 Huallanca Hydro-electric Project .... 36 4.9.4 Landuse ............................................. 36

4.10 Risk management ................................ 37

4.10.1 Lake security measures ................ 37 4.10.2 Monitoring ...................................... 38 4.10.3 Vulnerability ................................... 38

4.11 Conclusions and recommendations . 38

5 LAGUNA ARHUEYCOCHA ........................... 40

5.1 Introduction ............................................ 40

5.2 Historical development of Arhueycocha .......................................... 41

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5.3 Lake security measures ........................ 41


5.4.1 Geomorphic setting .......................... 41 5.4.2 Moraine dam ...................................... 43 5.4.3 Arhuey Glacier .................................. 44 5.4.4 Constraining rock slopes................. 45

5.5 Hazard assessment ............................... 45

5.5.1 Moraine complex............................... 45 5.5.2 Potential trigger mechanisms ......... 47

5.6 Risk management .................................. 47

5.6.1 Monitoring ......................................... 47 5.6.2 Lake security measures – recommendations ............................ 48

5.7 Conclusions ........................................... 48

6 LAGUNA LLACA............................................ 49

6.1 Introduction............................................ 49

6.2 Lake security measures ........................ 49

6.3 Present condition of Laguna Llaca and glacier ............................................. 50

6.3.1 Glaciological setting......................... 50 6.3.2 Llaca Glacier...................................... 51 6.3.3 Moraines ............................................ 52

6.4 Discussion.............................................. 52

6.4.1 The GLOF Source Parameter system................................................ 52 6.4.2 Affect of remediation on hazard status ................................................. 53 6.4.3 Current hazard status....................... 54 6.4.4 Future development of hazards ...... 54

6.5 Recommendations ................................ 55

6.6 Conclusions ........................................... 55

7 NEVADO HUASCARÁN ................................ 56

7.1 Introduction............................................ 56

7.2 Physical and geological setting ........... 56

7.3 Historical aluvión events ...................... 56

7.4 Field observations of Nevado Huascarán ................................ 57

7.5 Managing the hazards and risks

from Nevado Huascarán ....................... 60

7.5.1 Hazard assessment and monitoring techniques..................... 60 7.5.1.1 Hazard assessment .................... 60 7.5.1.2 Monitoring ................................... 60 7.5.2 Risk reduction ................................... 62 7.5.2.1 Reducing hazard ......................... 62 7.5.2.2 Reducing vulnerability ................. 62

7.6 Recommendations................................. 62

8 SOCIO-ECONOMIC STUDY OF COMMUNITIES WITHIN THE AREAS OF LLANGANUCO AND SANTA CRUZ ....... 63

8.1 Introduction ............................................ 63

8.2 Approach: risk perception .................... 63

8.3 Methodology .......................................... 63

8.4 Summary of findings ............................. 64

8.4.1 Information from focus groups with local inhabitants ....................... 64 8.4.1.1 Concepts and perceived vulnerability................. 64 8.4.1.2 Response strategies ................... 64 8.4.1.3 Resettlement ............................... 65 8.4.1.4 Attitudes towards risk management ............................... 65 8.4.2 Information from interviews with organisations and authorities ......... 66 8.4.3 Information from the community risk perception workshop ....................... 66 8.5 Conclusions ........................................... 67

8.6 Recommendations................................. 68

9 Summary ........................................................ 69

References.............................................................. 71 Appendix: Itinerary of RGSL staff ....................... 73 General notes

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April 2003 Issue 1.0 1

Methods of glacial hazard assessment and management in the Cordillera Blanca, Peru

1 INTRODUCTION 1.1 Terms of Reference Reynolds Geo-Sciences Ltd was appointed by the Department for International Development (DFID) to develop and facilitate cost-effective, socially acceptable and sustainable disaster preparedness and risk minimisation strategies through improved glacial hazard assessment and socio-economic vulnerability analysis. The work was to be carried out under DFID Knowledge and Research contract number R7816 dated 23 August 2000. Staff from RGSL were in Peru from 25th July to 29th August 2002 for knowledge transfer and testing of the appropriateness of hazard assessment procedures developed in the other key study site of the project, the Khumbu Himal, Nepal. This document represents the activity report for this visit in accordance with the above contract. Included are the methods, data and findings from the visit of RGSL staff, with information from Peruvian partners and sub-contractors included where appropriate. An itinerary of the visit is given as Appendix 1. 1.2 Aims and objectives The purpose of the trip was to work closely with staff of the Unidad de Glaciología y Recursos Hídricos (Unit of Glaciology and Hydrology) within the Instituto Nacional de Recursos Naturales (National Institute of Natural Resources; INRENA) in order to: a) Review the key glacial and related hazard types, with examples of past events, affecting Peru and the Cordillera Blanca region in particular. b) Examine information held within INRENA’s archives at the Glaciology Unit in Huaraz. c) Establish and evaluate past and current procedures for hazard assessment, risk assessment, and hazard/risk management in Peru and the Cordillera Blanca region in particular. d) Identify specific areas of interest, problems and priorities being addressed by the Unit of Glaciology in Huaraz. e) Collect field data from sites that met the DFID project requirements for testing of generic hazard and risk assessment procedures whilst, wherever possible, meeting the priorities of INRENA.

f) Collect field data/information about the perceptions and management of hazards and risks at the local level, including a socio-economic evaluation by sub-contractors Asociación SER. g) Provide the necessary information for the subsequent testing and modification of generic guidelines for hazard and risk assessment developed previously in the project, and to enable recommendations to be made to INRENA for hazard/risk management at specific sites and to INDECI at a strategic level in Peru. Four field sites were visited to collect the necessary information to meet the above objectives (Figure 1.1). These were, together with the rationale for each: �� Raucolta Glacier - to test theories of lake development and the early recognition of lake development as a predictive tool (Chapter 3). �� Laguna Safuna - to research the effect of a recently reported avalanche and large displacement wave (80 m+ high), to undertake, and assess procedures for, hazard/risk assessments, and to make recommendations for remedial measures if necessary (Chapter 4). �� Laguna Arhueycocha - to undertake, and assess procedures for, hazard and risk assessments at a lake that had already undergone partial remediation; to assess the affect of the first stage of remediation upon lake security (Chapter 5). �� Laguna Llaca - to review the affect of remedial measures on lake security; and to look at appropriateness of remedial works in the light of recent changes in the glacier/lake environment (shifting hazard zones with glacier change linked to climate change) (Chapter 6). Additionally, one day was spent with Ing. William Tamayo and Ing. Jesus Gomez, both of INRENA, visiting several locations with good views of Nevado Huascarán. The purpose was to obtain photographs of the western face of the massif that has been a regular source of rock/ice avalanches to aid INRENA in planning a monitoring strategy (Chapter 7).

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Fig. 1.1: Location of sites.

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2 THE MANAGEMENT OF GLACIER-RELATED RISKS IN THE PERUVIAN CORDILLERAS 2.1 Introduction In order to establish the background to the management of glacial hazards in Peru, information has been supplied by the current staff of INRENA, especially Ing. Marco Zapata and Ing. Nelson Santillan; also by Ing. César Portocarrero, the former head of the Unit of Glaciology in Huaraz before the privatisation of ElectroPerú in 1996; and from discussions with former employees including Ing. Alcides Ames. Much of the following section is based on the input of these people. A flood of water and debris (known in Peru as aluvión) from the glacial lake Laguna Cojup on 13th December 1941 is considered to be the starting point of studies related to glaciers and their hazards in Peru. The aluvión inundated the northern part of Huaraz in the Cordillera Blanca with the loss of at least 4,000 lives. Early research recognised two possible causes of the flood: either a rupture of a moraine dam by filtration removing fine material (piping); or more likely, by an avalanche of ice into the lake generating a violent surge (displacement wave) that overtopped the dam and lead to the outburst of much of the lake’s volume. It appears that these first studies in response to the 1941 disaster were driven by a practical purpose rather than by academic interest. The search for glacial lakes, potentially dangerous lakes and examples of past aluvión events marks the beginning of scientific study of glacial hazards in the country. Lakes formed as a result of glacier retreat have in some cases partially drained and at other times drained completely. The resulting flood scars and deposits can be found in many valleys that have, or had, glaciers high in their catchments. Some recorded aluviones for which the details are known are shown in Table 2.1. It is clear from the distribution of aluvión deposits that many more events have occurred and that some of these were of a very great magnitude. 2.2 Deglaciation and hazard formation in Peru It appears that there is a certain synergy between Late Quaternary and Neoglacial glacial fluctuations in Peru and those recorded in North America and Western Europe. Evidence from moraines adjacent to the Quelccaya ice cap in the Cordillera Vilcanota and from ice cores drilled in the saddle of Nevado Huascarán (Thompson et al., 2000) suggests that the maximum of the last major glacial period (the Last Glacial Maximum, LGM) occurred about 20,000 yrs BP (Thompson, 2000). The warming of the current

interglacial appears in Peru to have begun c. 11,000 yrs BP, to be interrupted by a cool period about 1500-1900 AD (often referred to as the Little Ice Age or Neoglacial period). Neoglaciation was characterised by small advances of glaciers and the consequent formation of distinct end-moraine ridges or ramparts, and it is behind these moraines that today’s glacial lakes have formed. Estimates of the amount and rate of glacier retreat in Peru following this cool period have been hindered by the type of available data, which often is in the form of photographs and observations rather than surveyed measurements. Snowline altitudes on Nevado Huascaran increased throughout the early 20th Century except for minor readvance between 1909 and 1932 (Table 2.2). In the last ten years, several studies have shown reductions in volume and extent, and negative mass balances of glaciers from Peru. For example, the Yanamarey glacier in the Cordillera Blanca reduced in volume by 22x106 ± 2x106 m3 from 1948 to 1982 and by 7x106 ± 0.2x106 m3 from 1982 to 1988 (Hastenrath and Ames, 1995). Similarly, Glacier Santa Rosa in the Cordillera Raura is experiencing 2 ma-1 (water equivalent) of surface lowering (Ames and Hastenrath, 1996). Ames and Hastenrath (1996) predict that the glacier will only survive a further 40 years under present conditions. Ice core records tell a similar story of warming and glacier recession. Ice cores from the Quelccaya and Huascarán ice caps show an increase in NO3

- and �

18O values over the last 200 years. Indeed, the �18O values for the twentieth centaury recorded in the Huascarán cores are the most enriched (i.e. warmest) of the last 6,000 years (Thompson, 2000). In addition, the comparison of ice cores from Quelccaya between 1979 and 1991 showed an attenuation of the seasonal �18O signal with depth. This isotopic smoothing is interpreted as the effect of increasing melt water percolating through the firn as the 0°C isotherm rises in response to warming (Davis et al., 1995; Thompson et al., 2000). Global warming has a number of potential consequences for glacial hazards. The formation and disappearance of ice- and moraine-dammed lakes, some of which may be dangerous, is often associated with changes in glacial extent (Haeberli and Beniston, 1998). Existing moraine-dams may experience accelerated degradation through melting of ice cores and their lakes may increase in volume due to greater meltwater input (Clague and Evans, 2000). Steep hanging glaciers that are partially or entirely frozen to their beds may become prone to ice avalanching as their snouts become warm-based (Haeberli et al., 1997). As many tropical glaciers exist close to the melting point (c.f. Thompson, 1980), continued glacier mass-balance losses will result in

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‘drastic water shortages’ after an initial period of increased discharge (Braun et al., 2000), a problem that is already of concern in Peru.

Table 2.1: Selected aluviones recorded in the Peruvian Cordilleras (based on information from INRENA and Reynolds, 1992). Note - Quebrada translates approximately as upper valley/meadow.

Date Event Reported losses March 1702 Inundation of the city of Huaraz January 1725 Aluvión affecting the city of Huaraz, unknown lake 1,500 people killed in Huaraz January 1725 Avalanche and aluvión from nevado Huandoy 1,500 people killed February 1869 Aluvión affecting the locality of Monterrey - Huaraz 11 deaths; loss of infrastructure February 1878 Aluvión affecting the locality of Huari Infrastructure June 1883 Aluvión from Lag. Tambillo affecting Macashca to the

south of Huaraz Infrastructure

January 1917 Avalanche from Nevado Huascarán towards Shacsha, Ranrahirca

Infrastructure

March 1932 Aluvión from Lag. Solterococha, near Pacllón to the south of Huaraz

Infrastructure

January 1938 Aluvión from Lag. Arteza affecting the Quebrada Ulta Infrastructure 1938 Aluvión from Lag. Magistral on the locality of

Conchucos - Province of Pallasca Infrastructure

April 1941 Aluvión from Lag. Suerococha, Cordillera Huayhuash Agricultural land December 1941 Aluvión from Lagunas Palcacocha and Acoscocha

near Huaraz 4,000 people killed in Huaraz; extensive damage to infrastructure

January 1945 Aluvión from Lagunas Ayhuiñaraju and Carhuacocha Destruction locally and to the historic ruins of Chavín

October 1950 Aluvión from Lag. Jancarurish Destroyed part of the Cañón del Pato Hydroelectric Power station; 200 – 500 deaths

July and Oct. 1951

Aluviones from Lag. Artesoncocha into Lag. Parón

November 1952 Aluvión from Lag. Millhuacocha affecting the Quebrada Ishinca

Infrastructure

March 1953 Aluvión from Lag. Tullparaju, near Huaraz Infrastructure December 1959 Aluvión from Lag. Tullparaju, near Huaraz Infrastructure January 1962 Avalanche and aluvión from Nevado Huascarán Norte 4,000 people killed and 9 towns

inundated December 1965 Avalanche and aluvión from Lag. Tumarina affecting

the locality of Acopara-Huari

May 1970 Avalanche of rock and ice from Nevado Huascarán Norte following major earthquake

Yungay buried; 23,000 deaths; damage to several towns and the Cañón del Pato Hydroelectric Power station

May 1970 Avalanche from Huascarán Norte into Lag. Langanuco 14 deaths May 1970 Avalanche from Nevado Artesonraju into Lag.

Jatuncocha

August 1982 Aluvión from Lag. Paclliash affecting the Quebrada Ishinca

Infrastructure

December 1987 Avalanche from Huascarán Norte Infrastructure January 1989 Avalanche from Huascarán Norte towards Ranrahirca Infrastructure December 1989 Aluvión from Lag. Chuspicocha affecting the city of

Huancayo Infrastructure

1996-1997 Series of ice avalanches into Lag. Salcantay, NW of Cusco

Environmental destruction in the Quebrada Aobamba and the confluence with the Río Vilcanota

January 1997 Auvión from Lag. Pacliashcocha, near Marcará Infrastructure May 1997 Aluvión from Artizón Baja, Quebrada Santa Cruz Trail destroyed Feb.-Dec. 1998 Aluviones from Nevado Salcantay affecting the

Quebrada Aobamba and Río Vilcanota Machupicchu Hydroelectric Power station destroyed - $160 million to rebuild and in lost revenue

April 2002 Rock avalanche into Laguna Alta Damage to terminal moraine; livestock killed

March 2003 Ice avalanche into Lag. Cojup or Palcacocha, near Huaraz

Water supply to Huaraz (population 100,000+) disrupted for 8 days

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Table 2.2: Snow line altitudes of Nevado Huascarán (Lat. 9°07' Long. 77°30') during the onset of deglaciation. Measurements were taken using a barometric altimeter (from Broggi, 1943). Author Year Altitude

(m) Error (m)

Increase (m)

Decrease (m)

Middendorf 1886 4320 + 50 - - Enock 1903 4420 + 50 100 - Peck 1906 4500 + 50 80 - Stevers 1909 4750 + 10 250 - Borchers 1932 4600 + 10 - 150 Broggi 1942 5100 + 50 500 -

Increase in snow line altitude during 56 years from 1886-1942 = 780 m. 2.3 The management of glacial hazards in Peru The incidence of aluviones in the late 1930s and early 1940s prompted the Government of Peru to begin a programme of study and remedial works to reduce and/or remove the risks of ice avalanches and glacial lake outbursts. Work began in the 1940s and accelerated in the early 1950s. Of the variables that affect the hazard of glacial lakes (strength of the dam including the presence of buried ice, potential landslides or ice avalanches into the lake, lake volume, etc.), the easiest to modify is the volume of the water. Consequently, the main type of treatment in Peru has been to reduce the volume of water by means of different procedures depending on the material properties of the dam of each lake. For moraine-dammed lakes the standard approach has been to use an open cut. Originally these were lined and capped with stone masonry, but later corrugated galvanised pipes up to 1 m in diameter were used. To provide protection against displacement waves, reconstructed stone- and/or concrete-faced earth dams are built over the channel. Initially these were less than 10 m high, presumably due to the lack of mechanical equipment at that time (40 to 50 years ago). The amount of lowering in each lagoon was determined on the basis of estimations and experience, with up to 10 m being normal (see Figure 6.4, Chapter 6, and the end of this chapter for examples). The aluvión from Huascarán Norte in May 1970 provided fresh impetus to the issue of glacial hazard management on account of the large scale of the event. Triggered by an earthquake measuring 6.8 on the Richter Scale, the collapse of the west face of the mountain mobilised up to 100x106 m3 of rock, ice and morainic material, which travelled at velocities of up to 250 kmh-1 or more before burying the towns of Ranrahirca and Yungay killing 23,000 people. More information on this event is provided in Chapter 7. After the earthquake, UNESCO sent a scientific mission to evaluate the extent of the damage

throughout the Cordillera Blanca region. The functions assigned to this Commission were to study lakes and landslides that could produce aluviones and threaten the proposed redevelopment of cities. Recommendations were made for the repair of dams damaged in the earthquake and new lakes were targeted for security work. The basic glacier management capability and experience developed in Peru since 1941 was dispersed after the privatisation of ElectroPerú in 1996. In 1999 the Unidad de Glaciología y Recursos Hídricos based in Huaraz was reformed and now exists within the Instituto Nacional de Recursos Naturales (INRENA). The Unit has a core staff of four scientists plus support personnel who are responsible for glaciological monitoring and the management of glacial hazards throughout the country. Its position has been strengthened through joint projects with other organisations to monitor glacier mass balance (University of Innsbruck, Austria), to record glacier runoff and catchment hydrology (IRD, France), to review aspects of glaciology and hazards (CONAM-INNAGA, Peru), and to consider regional and national strategies for hazard and risk management (RGSL, UK). In the short time since the group was reformed it has recognised the need to re-evaluate the status of glaciers and glacial lakes; a decision vindicated by outbursts from Laguna Safuna Alta in 2002 (see Chapter 4) and Laguna Palcacocha in 2003. The value of remedial works is thought to be demonstrated by the relatively low frequency of lake outbursts in Peru when compared to other countries where remedial work is not routinely undertaken (Figure 2.1). It also appears that there has been a decrease in the frequency of events in Peru since remedial works became more common in the 1950s (Figure 2.1), although the small sample size is not statistically significant. 2.4 Remediation of glacial lakes Laguna Palcacocha, sometimes also known as Laguna Cojup, at the head of Quebrada Cojup, was the first glacial lake to be remediated in Peru, work being undertaken between 1942 and 1943. Following the aluvión in 1941, the volume of Laguna Palcacocha was estimated at 880,000 m3. An open cut through the moraine dam was constructed in order to lower the lake level by 3.8 m, reducing the volume to 500,000 m3. Later, the channel was damaged by the 1970 earthquake and more work was undertaken to repair the damage and lower the lake further (Figures 2.2 and 2.3). Following this work it was thought that the lake no longer represented a risk. Interestingly, as this report was

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0

5

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15

20

25

30

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1920 1930 1940 1950 1960 1970 1980 1990 2000 2010Year

Cum

ulat

ive

freq

uenc

y

Himalayas

Peru

Trendline (Himalayas)

Trendline (Peru)

Fig. 2.1: Comparison of cumulative frequencies of reported glacier-related hazards in Peru and south central Asia since 1930.

Fig. 2.2: Laguna Palcacocha, Quebrada Cojup, to the east of Huaraz (photo César Portocarrero, 1966).

Fig. 2.3: The moraine dam at Laguna Palcacocha in 1973. The reconstructed dam is on the right of the picture. (Photo César Portocarrero, 1973). being finalised, news was received of an ice avalanche into Laguna Palcacocha that disrupted the water supply to Huaraz for 8 days. Details of the event are not known, but unexpected risks clearly remain in the Cordillera Blanca. In this case, it would be interesting to ascertain the affect of the security works, particularly whether they prevented a greater catastrophe. Thirty-eight glacial lakes in Peru now have security works. These are mainly in the Cordillera Blanca within the Río Santa river basin (Table 2.3). Styles of

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remediation include siphons, open channel (rare), channel with reconstructed dam, and tunnels through both moraine (above the water line) and rock (beneath the water line). Figures 2.4 to 2.9 show examples from some of these construction projects. Table 2.3: Glacial lakes with remedial works in the Río Santa basin, Cordillera Blanca. T = tunnel; OC = open cut; AD = artificial dam; C = canal; S = Siphon.

Name Sub basin Altitude Initial Volume (m3)

Final Volume (m3)

Draw down (m)

Type of works

Finish date

Safuna Alta Quitaracsa 4,291 7,002,500 38 T 1973 Pucacocha Quitaracsa 4,490 8,924,060 2,578,700 5 OC-AD 1968 Llullacocha Quitaracsa 4,735 5 OC 1979 Cullicocha Los Cedros 4,607 70,485,566 63,140,000 8 T 1951 Yuracocha Santa Cruz 7,380,000 OC-AD Taullicocha Santa Cruz 4,418 2,500,000 2 OC 1962 Jatuncocha Santa Cruz 3,880 5,400,000 5,400,000 OC-AD 1969 Arhuaycocha Santa Cruz 4,429 9,675,484 8,500,000 8 OC 2000 Paron Paron 4,155 78,500,000 7,300,000 52 T 1984 Huandoy Paron 4,738 2 OC 1974 Llanganuco Alta Llanganuco 3,833 1,717,000 OC 1971 Llanganuco Baja Llanganuco 3,820 12,030.000 12,030,000 C Laguna 69 Llanganuco 3,113,920 OC Artesa Buin 4,340 15 OC 1961 Huallcacocha Buin 4,345 5,646,300 3,800,000 10 OC-AD 1976 Cochca Hualcán 4,528 946,400 3 OC 1953 Rajupaquinan Hualcán 4,523 2 OC 1953 Laguna 513 Hualcán 4,400 25 S-T 1994 Lejiacocha Marcara 4,620 1,486,550 6 OC-AD 1953 Paccharuri Marcara 4,470 10,746,000 7,599,000 10 OC-AD 1986 Pucaranracocha Marcara 4,390 3,323,100 2,953,100 2 OC 1976 Aquillpo Marcara 4,720 8 OC Pacliashcocha Marcara 4,612 5,000,000 3,500,000 8 OC 2000 Ishinca Paltay 4,950 6 OC-AD Pacliash Paltay 4,607 4,620,000 3,500,000 6 OC 2000 Mullaca Huaraz 4,606 4 OC-AD 1953 Llaca Llaca 4,474 749,000 299,400 10 OC-AD 1977 Palcacocha Quillcay 4,566 579,400 514,800 1 OC-AD 1974 Cuchillacocha Quillcay 4,620 3,014,000 2,230,000 5 OC-AD 1973 Tullparraju Quillcay 4,300 1,620,000 33 T 1974 Cayesh Quillcay 4,740 OC Shallap Quillcay 4,270 4,755,000 3,550,000 7 OC-AD 1974

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Fig. 2.4: (a) Moraines and the hanging glacier at Laguna Cuchillacocha, where (b) a 5 m deep channel and a reconstructed dam were built in 1973 to provide 16 m of freeboard (photos César Portocarrero).

Fig. 2.5: (a) A combined channel and dam, at Laguna Shallap, where the water level was lowered by 7 m and (b) a dam 16 m high was constructed (photos César Portocarrero).

a

b

a

b

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Fig. 2.6: Construction of security works at Paccharuri; (a) open channel through the end moraine to draw the water level down by 10 m, and (b) assembling the channel lining before construction of the 20 m high dam (photos César Portocarrero, 1986).

Fig. 2.7: (a) Siphons to lower Laguna 513 in the Hualcán massif, north-east of Carhuaz (photo César Portocarrero); (b) subsequent tunnel construction to achieve permanent drawdown of 20 m (photo John Reynolds, 1992).

Fig. 2.8: (a) Laguna Cullicocha, in the northern Cordillera Blanca, following drawdown by tunnel in 1951 (note the shoreline); (b) floodgates and channels were installed to regulate the flow for the Cañón del Pato HEP station further down stream (photos César Portocarrero).

a a

b

b a

b

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Fig. 2.9: Security works at Laguna Parón. (a) Hatunraju glacier and moraine damming Laguna Parón before drainage; (b) construction of the first tunnel for 1,400 m through bedrock on the north side of the lake; (c) probing to establish the distance from the first tunnel to the lake; (d) drainage of the lake at a rate of 8 m3s-1; (e) installation of a second tunnel with valves to regulate the flow for the Cañón del Pato HEP station; (f) the lake today, with the former shoreline still visible. Photos (a) by J. Alean, 1982, in Hidrandina (1988); (b), (c), (d) and (e) by César Portocarrero.

e

d

c

b

a

f

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March 2003 Issue 1.0 11

3 RAUCOLTA GLACIER 3.1 Introduction Raucolta Glacier is a 3.2 km long valley glacier located at the head of Quebrada Raucolta in the northern Cordillera Blanca (Figures 1.1 and 3.1). Prior to fieldwork, inspection of topographic maps and an ASTER satellite image acquired on 17th August 2001 highlighted several small lakes on the surface of the glacier and that the tongue had a low average surface gradient (≤2.5º). Reynolds (2000) identified a positive correlation between the distribution of large lakes and glacier surface gradients of 2º or less from studies of debris-covered glaciers in Bhutan. He therefore suggested that glacier gradients can be used as a simplistic, yet effective means of identifying areas where potentially dangerous lakes may develop. As the gradient of Raucolta Glacier lay close to the threshold of Reynolds (2000), and small lakes were already present on the glacier surface, the site was chosen for further investigation. The site was visited from 15th to 18th September 2001 to field truth the available remote sensing information, to investigate processes associated with current lake development, and to consider the future hazard

potential of Raucolta Glacier. RGSL staff were accompanied by researchers from the University of Wales, Aberystwyth, as part of a complementary project to develop improved remote sensing techniques for glacial hazard assessment. Examples of the selected results from this other project have been included within this report to illustrate the potential of the techniques. 3.2 Theories of lake development Moraine-dammed lakes can develop quickly such that ‘in many occasions the first time the existence of a lake becomes apparent is when it floods communities downstream’ (Richardson and Reynolds, 2000a, 36). In Nepal for example, Tsho Rolpa, Imja, Lower Barun and Thulagi have all appeared within the last 30-45 years and are expanding in length at rates of 33-71 ma-1 and in depth by 3 ma-1 (Fig. 6; Richardson and Reynolds, 2000a). Perhaps the fastest development of a dangerous lake reported is that of Laguna 513 in the Cordillera Blanca, 12 km to the northeast of Carhuaz. Laguna 513 was a c. 1.2 m long lake that formed entirely between 1988 and 1992, and was subsequently remediated by a tunnel through the bedrock-cored end-moraine (Reynolds et al., 1998).

Fig. 3.1: Raucolta Glacier and Quebrada Raucolta as seen on an ASTER image from 17th August 2001.

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There are two main situations in which lakes form within a damming moraine complex (cf. Richardson and Reynolds, 2000a). Relatively short glaciers tend to have steep surfaces that allow free drainage of melt water, which may then collect behind moraine ridges to form a lake (e.g. Laguna 513, Cordillera Blanca). Relatively long glaciers tend to have low angle snouts and respond to negative mass balances by thinning rather than recession up valley. Their frontal positions often remain stable, particularly where debris covered. Drainage is impeded by stagnant ice and/or a moraine ridge and a lake develops, with a new active front calving into the lake (e.g. Tsho Rolpa, Nepal; Reynolds, 1998). By insolating ice from solar radiation and diurnal temperature fluctuations, a debris-cover more than a few cm thick inhibits ablation (Kayastha et al., 2000). However, where crevasses or other features break this debris mantle, local ablation rates may be high, especially around the margins of supraglacial lakes with bare ice cliffs (Kirkbride, 1993; Kirkbride and Warren, 1999; Benn et al., 2000, 2001; Sakai et al., 2000). Therefore, the response of debris-mantled glaciers to climate forcing is non-linear, with slow sub-debris mantle melting leading to a threshold at which point rapid lake growth by calving becomes the dominant ablation mechanism (Kirkbride and Warren, 1999; Richardson and Reynolds, 2000b; Benn et al., 2001). Many debris-covered valley glaciers are out of equilibrium with climate and will cross this threshold in the coming decades even if the current warming trend halts or is reversed (Naito et al., 2000). Recent research into the development of glacier lakes has been focused in the Himalayas. Ngozumpa Glacier in the Khumbu Himal of Nepal has been studied in detail as it is downwasting and is thought to lie on the threshold for moraine-dammed lake formation (Benn et al., 2000, 2001). Numerous supra-glacial ponds in closed basins are ‘perched’ above the en-glacial drainage of the Ngozumpa Glacier. Such lakes were observed to expand through three main mechanisms, sub-aerial melting, thermo-erosional notching at the waterline and calving, until they intercept en-glacial conduits, at which point they drain. Nearby meteorological data suggest that differences in the water balance between years when the lakes increased was small. However, calculated input from calving and debris supply match increased lake volume well, suggesting that calving is the main cause of increased lake levels (Benn et al., 2000, 2001). With little melt below the thick debris mantle of the glacier, supraglacial ponds contribute greatly to the ablation and reduction in angle of the glacier surface. Heat budget observations on a glacier neighbouring Ngozumpa Glacier show that ponds and their ice

cliffs absorb seven to ten times more heat than adjacent debris-covered ice (Sakai et al., 2000). At least half of this absolute heat is released with the outflow, causing enlargement of englacial conduits, which may collapse forming new ponds; a positive feedback process (Sakai et al., 2000). Analysis of relatively long glaciers with moraine-dammed lakes has shown that low glacier surface angle (<2º) is a condition for lake growth (Reynolds, 2000). When the glacier surface lowers sufficiently the growth-drainage cycle of perched lakes will cease, as they intersect the base level. On the Ngozumpa Glacier the perched lakes do not grow indefinitely, but a spillway over a lateral moraine provides a local base level for one lake. Benn et al. (2000, 2001) suggest that this lake can only increase in volume and area with continued negative mass balances. Given the low angle of Ngozumpa Glacier and the processes described by Benn et al. (2001), a lake larger than those currently causing concern in the region is likely to form. The processes of lake development for debris covered glaciers in Peru are likely to be similar to the observations from Nepal (Benn et al., 2000, 2001) and New Zealand (e.g. Kirkbride and Warren, 1999). 3.3 Historical development of Raucolta Glacier Stereo aerial photographs from September 1948 and May 1963, and an ASTER satellite image from August 2001 have been used to provide information about the evolution of Raucolta Glacier. Digital Elevation Models (DEMs), at 10 m spatial resolution, have been produced from the aerial photographs using digital photogrammetric techniques. This work was undertaken through a non-commercial research exercise between RGSL, the University of Wales, Aberystwyth, and the Department of Geography, University of Zurich. Examples of the DEM are shown here courtesy of the University of Zurich to illustrate the potential of remote sensing techniques to identify spatial and temporal changes of debris-covered glaciers. A 30 m resolution DEM from the ASTER imagery was obtained from the USGS Data Centre. The DEMs combined with draped imagery for each year show a similar glacier form between 1948 and 2001; a very low angle snout, a prominent end-moraine ridge, and no evidence of a spillway over the end-moraine (Figure 3.2). A profile of the glacier long axis taken from the 1963 aerial photograph DEM shows that the average surface gradient of the glacier within 450 m of the end-moraine crest was very close to horizontal. The surface gradient increases to an average of 2º for a further 500 m and then to 5.8º until the base of the icefall. Comparison of profiles from the 1948 and 1963 aerial

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photographs highlights an area of downwasting within the sub-horizontal lowermost 450 m (Figure 3.3). Up glacier, the change in surface elevation between the 1948 and 1963 DEMs is much more chaotic, perhaps indicating more active ice. A notable 15 m+ low point on the 1948 and 1963 cross-sections marks the transition of the low angled downwasting ice to the steeper angled ice up stream.

Fig. 3.2: Historical development of Raucolta Glacier as displayed in imagery draped over Digital Elevation Models produced from (a) stereo aerial photographs from 1948; (b) stereo aerial photographs from 1963; and (c) ASTER satellite data from 2001. (a) and (b) courtesy of University of Zurich, (c) supplied by USGS Data Centre.

The profile from the ASTER DEM gives the impression of net downwasting between 1963 and 2001, although the information should be viewed with caution. It was necessary to adjust the ASTER DEM to match the DEMs from the aerial photographs in the area of the end-moraine (assuming this point has undergone least change). The apparent maximum change in vertical position of the glacier surface (c. 20 m) lies within the expected precision of the ASTER DEM (which can be up to 50 m in the z direction for mountainous terrain). Small supraglacial ponds are visible on all of the available imagery. Individual ponds are not present on multiple images, indicating that they are transient and drain readily. The area of ponds has varied, but the total amount of supraglacial water has remained low throughout the period covered by the imagery. 3.4 Field observations 3.4.1 Glaciological setting Accumulation for Raucolta Glacier is from the steep west face of Nevado Santa Cruz (6,241 m), presumably through a combination of avalanching and direct snowfall. Ice from the single accumulation basin passes through an ice fall and flows into the 1.5 km long debris-covered tongue (Figure 3.5). The tongue is contained within a well-defined latero-terminal moraine ridge, the crest of which is c. 110 m above the valley floor at the highest point at the snout. This Neoglacial moraine is the youngest and best developed of six moraine ridges in the upper Quebrada Raucolta (the four most recent are shown on Figure 3.4), suggesting at least five more extensive glaciations, the dates of which are not known. Well-developed ablation valleys lie on both sides of the Neoglacial moraine ridge. The right (northern) ablation valley is fed by scree from three small mountain glaciers high on the north valley side, whilst the southern valley side comprises predominantly bedrock cliffs. 3.4.2 Structure of Raucolta Glacier Raucolta Glacier snout can be divided into two morphologically distinct areas. The lower c. 500 m of the snout has a near horizontal gradient, is characterised by irregular hummocks of the order of 15 m high, and the glacier margins are partially obscured by the slumped inner flanks of the bounding moraine ridge. Ice is occasionally exposed throughout the area and a few small ponds are present (Figure 3.6). The snout area is separated from ice further upstream by a series of transverse ice cliffs c. 500 m from the end-moraine crest (Figure 3.7). The morphology of the upstream ice is

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Fig. 3.3: Long profiles of Raucolta Glacier terminus. 1948 and 1963 aerial photograph DEM data supplied courtesy of University of Zurich; 2001 ASTER DEM data supplied by USGS Data Centre.

Fig. 3.4: Distribution of ponds on the surface of Raucolta Glacier, 1948-2001. 1948 and 1963 data obtained from aerial photographs, 2001 diagram based on ASTER satellite data.

Fig. 3.5: Raucolta Glacier. Note the debris-covered tongue, well-developed Neoglacial moraine ridge and single accumulation basin on the west flank of Nevado Santa Cruz (6,241 m). markedly different to that of the lower snout area; the relief is less pronounced with smaller (up to c. 5 m high) but more regular transverse ice cliffs and there is an apparently thinner yet more uniform debris layer up to c. 1 m thick. From ice exposed at the glacier surface and in the ice cliffs, the structures of Raucolta Glacier appear to be relatively simple. Transverse and longitudinal crevasses are displayed in the icefall (Figure 3.8a), through which the ice from the accumulation area flows as a single unit. Transverse foliation is exposed at the base of the icefall beneath the snow

© Mike Hambrey

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Fig. 3.6: Hummocky topography of the lower Raucolta Glacier snout indicative of ablating stagnant ice. line (Figure 3.8b). The foliation is convex down-glacier, dips up-glacier and is associated with tight isoclinal folds. Further downstream, near the series of prominent ice cliffs, the foliation dips up-glacier by 30-45º in longitudinal cliff faces and dips towards the centre line of the glacier by 60-70º in transverse cliff faces close to the glacier edges. The geometry of

the foliation is similar in form to a series of stacked spoons and is indicative of classical flow patterns associated with a simple valley glacier with fastest flow close to the upper regions of the centre line (Harbor, 1992).

Fig. 3.7: Transverse ice cliffs (numbered 1-3) separating the stagnating glacier snout (bottom left) from more active upstream ice (top right).

Fig. 3.8: Structures of Raucolta Glacier: (a) transverse and longitudinal crevasses in the ice fall; (b) folded transverse foliation at the foot of the ice fall; (c) thrust exposed in an ice cliff at the upstream end of the stagnating glacier snout; and (d) interpretation of (c).

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A series of structures believed to be associated with a thrust are exposed in an ice cliff on the left side of the glacier at the upper end of the hummocky, stagnant terminus ice (Figure 3.8c, d). A crevasse filled with debris and ice breccia dips up-glacier at 34º and is interpreted as a thrust plain. This structure can be traced across the cliff for 30 m and becomes lower in angle as the ice cliff becomes increasingly transverse towards the glacier edge. Foliation is overturned beneath the interpreted fault plane and has been displaced along associated extensional brittle fractures above the plane. Displacement on the fault is of the order of 1-2 m. There is a subtle transverse ridge of sediment associated with the surface outcrop of the fault that may be a thrusted sediment ridge. If this area is an active thrust zone, it suggests accommodation of strain is occurring between more active ice upstream and less active ice downstream. 3.4.3 Ablation of Raucolta Glacier Fresh and apparently active backscarps are present around much of the inner flank of the lateral and end-moraine complex. Particularly affected is the left lateral midway along the glacier and near to the end-moraine (Figure 3.6), the end-moraine immediately to the right (north) of a former spillway (Figure 3.9), the northwest corner of the moraine complex, and midway along the right lateral adjacent to the location of the prominent transverse ice cliffs. Current downwasting of the entire glacier surface is inferred, with the largest amount having occurred in the mid reaches of the snout adjacent to the large rotational failures on the left lateral and the slumps midway along the right lateral. This process would have led to the flattening of the surface gradient of the lower 500 m of the glacier snout.

Fig. 3.9: Active backscarp associated with slumping on the inner flank of the end-moraine ridge.

3.4.4 Hydrology of Raucolta Glacier Ponds on the glacier surface occur mainly at the foot of the ice cliffs across the mid reaches of the glacier and in the upper reaches of the debris-covered snout. Growth of ponds appears to occur through melting and undercutting of ice at the water line (Figure 10a), sub-aerial melting of ice cliff walls (Figures 3.8c and 3.10b) and by calving sub-parallel to the cliff (Figure 11c). In some cases, the boundary of ponds and englacial conduits are associated with pre-existing glacier structures (Figures 3.8c and 3.10b), but in many more cases the position of ponds appears independent of glacier structure (Figures 3.6, 3.7, 3.8b, 3.10a). A pond visible in the 2001 ASTER image has since drained. Englacial tunnels were seen in association with a pond near ice cliff 1 (position shown in Figure 3.7) and a pond in the lower reaches of the snout (Figure 3.10b). Interception of a conduit during pond growth is proposed as the most likely mechanism for the subsequent pond drainage (c.f. Benn et al., 2001). Despite the evidence for glacier decay, there are few supraglacial lakes and little evidence for supraglacial drainage now or in the past. There is no sub-aerial drainage from the glacier over the moraine or in either ablation valley. Meltwater was seen flowing in the upper reaches of the glacier from the clean ice/debris-covered ice transition. The stream flowed into a conduit after a distance of about 100 m. No other meltwater streams were observed, although water could be heard flowing into the glacier from the margins of ice cliff 1. There is no drainage over the end-moraine complex. Several springs emerge from the foot of moraine complex number 4 against the north side of the valley 1 km from the snout of Raucolta Glacier. It is thought that the springs are meltwater fed as no other meltwater outlet or source for the springs was found. Connectivity between the springs and the glacier hydraulic network has not been proven. 3.5 Interpretation The hummocky surface morphology of the lower 500 m of Raucolta Glacier snout and evidence for downwasting (historical from the aerial photographs and contemporary from slumping of the moraines) is evidence that the glacier terminus is decaying in situ. Downwasting appears to have been greatest in the mid reaches of the debris-covered snout, where moraine slope failures are greatest, and this trend has been evident since 1948, the date of the first aerial photographs. A net result of differential downwasting has been the gradual flattening of the

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Fig. 3.10: Supraglacial ponds: (a) near the upper limit of the debris cover, showing notching and melting beneath at water line; (b) near to the snout, showing exposed englacial tunnel. surface gradient of the glacier such that the lower 500 m are now nearly horizontal. The distinct change in morphology 500 m from the end-moraine, with less relief, sharper glacier boundaries and a steeper surface gradient, implies that flow is still occurring upstream of the series of transverse ice cliffs. It is thought that these cliffs mark the boundary between the active ice upstream and the stagnant ice downstream. Accommodation of strain between the active ice and the stagnating tongue is manifest as thrusting, as shown by the thrust plane observed in an ice cliff about 500 m upstream of the end-moraine ridge. The extent of thrusting is not known. Debris with a sub-glacial signature has been found on the surface further down-glacier (Michael Hambrey, pers. comm.), possibly indicating thrusting over a wider area, although not necessarily contemporaneously. Most of the surface of the glacier is remarkably free of meltwater. Raucolta Glacier seems to be freely drained with meltwater flowing into the glacier, through or beneath the end-moraine sediments and emerging from springs a further 1 km down valley. A well-developed englacial drainage system would allow for the regular drainage of any ponds that

develop, although the detail of the englacial conduit system is not known. It is thought that permeability within the end-moraine complex must be high. Debris upon the glacier and within the lateral moraine appears relatively coarse and blocky, and in places is clast-supported (Figure 3.11). Descriptions and samples of the ground moraine were collected by colleagues from the University of Wales, Aberystwyth. When these are analysed they may provide further information about the properties of the moraine.

Fig. 3.11: Coarse blocky sediments (a) on the glacier surface, and (b) in the left lateral moraine. 3.6 Implications for glacial hazard evaluation

3.6.1 Potential for lake development Downwasting of the glacier and the presence of small ponds throughout the debris-covered terminus indicate that conditions are conducive to the generation of meltwater. Given current drainage conditions however, it is likely that meltwater will continue to drain freely. It would require a change in the drainage network to raise the glacier base level before ponds could become more pervasive and coalesce to form larger lakes. The point in the mid reaches of the glacier marked by the transverse ice cliffs is of particular importance to

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the development of potential hazards. In this area there is a change of ice dynamics as indicated by the thrusting. It is thought that there is a causal relationship between the change in ice dynamics and the development of the transversely extensive cliffs. Exposed ice in the cliffs and ponds at the base of the cliffs will only serve to exacerbate the rate of downwasting in this area. A concern is that these cliffs are developing as the new dynamic snout of the glacier. This process has been inferred at many sites where a supraglacial lake has formed thereby separating a debris-covered stagnant snout from a calving ice terminus at the upstream end of the lake (Richardson and Reynolds, 2000a) but has not been documented before. It is not known how the ponds will develop in this area and whether this could be a precursor to lake growth and calving retreat of the ice cliffs. Should current drainage be impeded, there are several indications that a lake up to several hundred metres long could form. The lower 500 m of the snout is stagnant, is melting as shown by the thermokarst topography and instabilities of the inner moraine flanks, and has a sub-horizontal surface gradient. The moraine ridge is continuous with no incised former drainage channels, and would therefore offer minimum freeboard to a lake. In addition, it is thought that the developing ice cliff could be exploited through calving allowing for lake expansion and providing a source of displacement wave triggers. 3.6.2 Glacier surface gradient as an indicator of

lake development potential The lower reaches of Raucolta Glacier have been below the 2º lake formation threshold of Reynolds (2000) since at least 1948 without a lake forming on account of favourable drainage conditions. The hydraulic base level within the glacier and moraine system is therefore a critical constraint within the surface gradient rule. Lower surface gradients may favour a higher average base level, but not necessarily if there is free drainage. Elevated base level conditions are favoured by impeded drainage, either through an inefficient conduit system, impermeable end-moraine and/or an impermeable reverse slope at the glacier bed (c.f. Kirkbride, 1993). Given an elevated base level, the lower the surface gradient of the glacier, the greater is the area over which ponds can coalesce to form a large lake. On account of numerous examples from Himalayan Glaciers (Reynolds, 2000), glacier surface gradient remains a valid first order indicator of potential lake growth on debris-covered glaciers. The example at Raucolta Glacier illustrates the importance of establishing hydrological, glaciological and geological

conditions through a more detailed ground investigation as the next step in hazard evaluation. 3.7 Recommendations As long as effective drainage of the Raucolta Glacier and moraine complex is maintained, it is expected that a lake will not form on the glacier surface. It is suggested though that the glacier should be periodically monitored every two or three years, either by a field visit or by using satellite imagery, to check that ponds are not coalescing and thereby indicating a change in drainage conditions. Preferably, satellite imagery would be multi-spectral and have a ground resolution of no less than 15 m so that lakes can easily be classified and potentially significant changes can be determined. Current suitable data sources include ASTER, Landsat ETM+ and the newly operational SPOT V satellites. If lake growth is observed during monitoring, it is suggested that an evaluation be conducted to consider factors that influence the likelihood of an outburst flood and those that determine the potential consequences down valley. Baseline data (e.g. topographic and bathymetric surveys) should be collected during any preliminary hazard assessment to allow for the subsequent detection and comparison of changes in the glacier/moraine/lake system. 3.8 Conclusions Raucolta Glacier was chosen for study because its average surface gradient lies close to the 2º threshold for lake development of Reynolds (2000) and supraglacial ponds visible in a 2001 ASTER image indicated that conditions were possibly conducive to lake formation. On close inspection in the field and from digital photogrammetric analyses of aerial photographs from 1948 and 1963 it was clear that the lower part of the glacier snout has been well below the 2º lake growth threshold since at least 1948, yet a large lake has not formed. Supraglacial ponds and streams all drain englacial and through, or beneath, the end-moraine to emerge as a series of springs 1 km down valley of the end moraine ridge. There is no evidence of sub-aerial drainage over the end-moraine. Analysis of glacier morphology and structures shows that Raucolta Glacier comprises a single flow unit and hence is structurally simple. The most significant features are a series of transverse ice cliffs c. 500 m from the snout. It is at this point that evidence of thrusting within the ice occurs, and regular surface lowering moves to less uniform changes up-glacier about this axis, suggesting that the cliffs mark the boundary between stagnant ice downstream and

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more active ice upstream. It is thought that the stagnant ice down valley of the ice cliffs has, or is in the process of, becoming dynamically detached from the more active upstream ice. Dynamic detachment has previously been inferred at other glaciers where an active ice cliff is separated from stagnant ice by a supraglacial lake, and the process was thought to be related to lake growth. At Raucolta Glacier the process is occurring without a lake, which raises the question whether thrusting and detachment of stagnant ice actually precedes lake development and expansion.

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4 LAGUNAS SAFUNA ALTA AND SAFUNA BAJA

4.1 Introduction In response to a request by INRENA, RGSL visited the Safuna valley from 4th to 10th August 2002. RGSL staff were JMR and APH with Duncan Quincey (TCS) and Bryn Hubbard (Univ. of Aberystwyth). Also present was an INRENA team of topographic surveyors and technicians, some twelve in number, under the leadership of Nelson Santillan. Marco Zapata (INRENA) and Alfredo Cacares (Eginor) were present on 7th August. 4.2 The setting of the Safuna lakes The Safuna lakes lie in the northern part of the Cordillera Blanca on the north side of the Nevados Pucajirca, close to 77o 37’ W, 08o 50’ S at an altitude of 4,354 m (Laguna Safuna Alta) as shown on Figure 4.1.

Fig. 4.1: Lagunas Safuna Baja and Safuna Alta. The Safuna Glacier and its tributary glaciers drain the north side of Pucajirca Oeste, Central and Norte each of which rises to slightly over 6,000 m. The glacier terminates at or close to Laguna Safuna Alta. Laguna Safuna Baja lies approximately 0.5 km further down valley from L. Safuna Alta and is 80 m lower in elevation, with a large moraine ridge between the two (Figure 4.2). Below the lakes, the waters join those draining the north-eastern side of Nevado Alpamayo

to form a small river flowing north-eastwards down the valley of the Quebrada Tayapampa. This area is used for the grazing of a large number of cattle and some horses and, a little lower, alpaca. Peruvian and foreign tourists were seen camping in this area.

Fig. 4.2: Lagunas Safuna Alta (right) and Safuna Baja (left) from the south-west. The few houses of Huillca stand beside the river at an altitude of 4,000 m, 5 km downstream from L. Safuna Baja. Other small settlements are scattered at intervals westwards along the base of the narrow valley (now known as the Q. Collota) until the village of Quitaracsa is reached 24 km downstream from L. Safuna Baja at an altitude close to 3,100 m. The river, now known as the Rio Quitaracsa, and having been augmented from the north by the waters of the Rio Racuay, flows westwards down the increasingly narrow valley of the Q. Quitaracsa. There are scattered settlements in the upper part of this section but further downstream these are precluded by the narrowness of the Quitaracsa gorge. The Rio Quitaracsa terminates 40 km downstream of L. Safuna Baja where it enters the Rio Santa, the major river of the western side of the Cordillera Blanca. The confluence occurs close to the hydroelectric power station at the foot of the Cañón del Pato of the Rio Santa and 1 km above the sizeable village of Huallanca that houses many of the workers from the power station. 4.3 The geological setting of the Safuna lakes The geological maps published by INGEMMET (Wilson et al., 1995) indicate the Safuna district to be underlain chiefly by Mesozoic rocks with more recent intrusions of granodiorite to the south and west and with Holocene glacial and fluvioglacial deposits covering the rocks in places. The map shows a major syncline 2 km to the east of the Safuna lakes, with its axis running NW – SE, sub-parallel to the axis of the Cordillera Blanca and also

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to the orientation of the Safuna lakes and upper valley. In the core of the syncline, including the eastern flank of the Safuna valley, the map shows the Santa Carhuaz Formation of the Lower Cretaceous. This is described as limestones, calcareous mudstones, mudstones and sandstones. Cropping out on either limb of the syncline, including along the western flank of the Safuna valley, the map shows the underlying Chimu formation, also of the Lower Cretaceous. This is described as hundreds of metres of quartzites, sandstones and mudstones with bands of anthracite. The Chimu Formation is underlain by the Upper Jurassic Chicama Formation and the map indicates this to underlie much of the district to the north-west and north-east of Safuna. It is reported to consist of mudstones and fine sandstones. However, to the south-west of Safuna these sedimentary formations are displaced by the granodiorites and tonalites of the Cordillera Blanca batholith that form much of the western and central parts of the range. Immediately south of the Safuna lakes, the geological map indicates glacial deposits, but in fact much of this area appears to be glacier ice occupying the high ground of the Pucajirca – Alpamayo – Santa Cruz massif. However, the map does show the valleys below the glaciers to be occupied by fluvioglacial deposits. This includes the Safuna valley and the Q. Tayapampa below, together with the Pucacocha valley to its west that drains the north-east side of Alpamayo. 4.4 Recent history of the Safuna lakes Laguna Safuna Baja is dammed by older moraine ridges and has remained substantially unchanged at least since the map of 1950. It is roughly a square of side 400 m. It is relatively shallow but it appears that its depth varies seasonally. A low-profile moraine ridge can be seen to create a shallow zone across the southern part of the lake but does not break the surface. The map of 1950 shows the Safuna glacier extending across the area now occupied by Laguna Safuna Alta, up to the large moraine ridge. However, a series of supraglacial ponds is shown on the north-eastern part of the glacier. Air photographs from 1962 show the ponds to have coalesced to form a small upper lake (Laguna Safuna Alta). During the 1960s this spread to the full width of the ice. By the late 1960s a topographic and bathymetric survey showed that the volume of the upper lake had reached 6 x 106 m3. The surface level of the lake was close to 4,380 m, 25 m above the level today and 105 m above the level of the lower lake. There was no surface outlet to the upper lake. The size and

rapid development of this lake were causing concern and, in order to limit any rise in water level, a tunnel was driven through the moraine a little above the level of the lake surface at the time. The tunnel was funded by the French and was completed in early May 1970. Thirty days after completion of the tunnel, on 31st May 1970, a Richter magnitude 7.7 earthquake occurred 130 km off the Peruvian coast and resulted in considerable damage and loss of life, particularly in and around the Cordillera Blanca. The main regional town of Huaraz suffered badly and the earthquake triggered the landslide that destroyed the town of Yungay. It has been estimated that 18,000 lives were lost at Yungay and some 70,000 in Peru as a whole. The tremor was felt by scientists who were visiting Safuna at the time. The tunnel was damaged and assumed destroyed by the earthquake. By some mechanism that is not entirely clear, the earthquake caused increased seepage of lake water through the moraine such that the water level fell 25 m and when the lake was resurveyed in 1973 its volume had decreased to 2 x 106 m3. Thus, although the relief tunnel had been seriously damaged (Figure 4.3), the effect of the earthquake also made it redundant.

Fig. 4.3: Distal portal of the 1970 tunnel showing toppled wing wall. During the 1970s the glacier continued to retreat and the lake grew in area though its surface level did not rise significantly. In 1978, a second tunnel was bored approximately 5 m above the new lake level to preclude any subsequent rise in the water surface. The lake continued to grow in area as the glacier retreated but the water level did not change significantly and the new tunnel did not come into operation during this period. A survey carried out in 2001 indicated the lake to be close to 1,200 m long, 132 m deep and 20 x 106 m3 in volume. The moraine dam provided 80 m of freeboard at its lowest point, but was generally closer to 100 m above the lake surface.

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Fig. 4.4: Laguna Safuna Alta showing the landslide that occurred on the 22nd April 2002. On 22nd April 2002, 10 x 106 m3 or more of rock fell from the western valley slope into the southern end of the lake and onto the surface of the glacier beyond (Figure 4.4). Investigation of the cause and effect of this landslip was the main purpose of this study and the details are discussed below. However, prior to the field visit it was clear that the wave resulting from the landslip falling into the lake had overtopped the moraine dam, i.e. it was at least 80 m high; that the second tunnel and spillway had been damaged and that at least 22 cattle grazing in the area had been killed; but that the moraine dam had remained substantially intact and the damage had been contained locally. 4.5 Lake remedial measures In 1970, because of the rapid growth of the upper lake and the significant head difference between the two lakes (approximately 105 m), there was understandable concern regarding the stability of the moraine. It was decided to limit any further increase in water level in the upper lake by constructing an overflow tunnel. In view of the permeable morainic material of the dam it was necessary for construction purposes to bore it just above the water level at that time. Thus it was constructed at a level of around

4,385 m to ensure a dry heading. It could not therefore be used to draw down the lake level but only to limit any further rise. The tunnel was horseshoe-shaped in section with a flat base and semi-circular crown and was lined with reinforced concrete including, at intervals, what appear to be short lengths of railway line, arched to form substantial ribs. At its outflow, the tunnel had a concrete and masonry spillway to prevent erosion to the distal side of the moraine when the tunnel started to carry water. It is understood that the tunnel was constructed by hand through loose morainic material with local use of explosives when larger boulders were encountered. Photographs taken at the time show that wooden shuttering was used to form the concrete lining. It appears that the tunnel never came into operation, at least until the events of April 2002. Following the major earthquake of 31st May 1970 that both damaged the tunnel and caused the water level in the upper lake to be lowered by 25 m, the lake continued to grow in length with the retreat of the glacier. As concern remained over the stability of the glacier, it was decided to take advantage of the lower water level, which may have been thought of as a

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temporary benefit, by driving a second tunnel through the moraine slightly above the new water level and thus limiting the lake to a new lower water level. The design and method of construction of the second tunnel and its spillway appear to have been very similar to those of the first. Engineering drawings show the tunnel to have been 156.7 m in length with a fall of 2.5 m and a gradient of 0.9o. The drawings show that a concrete and masonry spillway, similar to that of the first tunnel, was constructed on the distal side. As the glacier retreated and the lake lengthened, the water level did not rise appreciably and thus it appears that the second tunnel did not come into operation, at least until April 2002. 4.6 Field observations 4.6.1 Bathymetric and topographic surveys During the RGSL field visit, INRENA staff carried out a bathymetric and topographic mapping exercise. Bathymetric mapping was carried out from an inflatable boat using an echo sounder. The location of each sounding measurement was determined by a signal from the boat to two surveyors stationed on the lateral moraine ridges on either side of the lake. The surveyors then took simultaneous sightings on the boat and its location was plotted by triangulation. The bathymetric survey indicated that the maximum depth of the lake was 81 m, constituting a reduction of over 38 m compared with the 2001 maximum, presumed to be a result of infilling with debris from the April 2002 rockfall. The deepest part of the lake had shifted to the southeast, the previously deepest part having been filled, reducing its depth by 47 m. The topographic survey was carried out by two surveyors, each operating with a team of ‘chainmen’. The area surveyed included the lateral and terminal moraine ridge that dams the lake, the ablation valley beyond on each side and some of the smaller moraine ridges beyond. It included the distal face of the moraine dam and the margins and surroundings of the lower lake. It also included the older and lower moraine ridge that encloses the lower lake, the distal face of that moraine and extended a considerable distance into the meadow beyond. 4.6.2 Moraine dam 4.6.2.1 Lateral moraines The distal flanks of the lateral moraines are largely well vegetated and have sharp ridge crests. The proximal flanks adjacent to Safuna Alta are significantly steeper, are far less well vegetated and in many places, have no vegetation at all. The

lowermost parts of the proximal flanks have suffered from attrition associated with the displacement waves from the landslide of 22nd April 2002 (Figures 4.5, 4.6 and 4.7). The proximal flanks of lateral moraines associated with Safuna Baja are also well vegetated right down to the shoreline of the lake. However, there is evidence of damage arising from the overspill of the displacement waves from Safuna Alta in the form of broken and uprooted vegetation and a veneer of fine sediment well above the present lake level (up to ~2.5 m above the observed lake level).

Fig. 4.5: Oblique aerial view of Laguna Safuna Alta.

Fig. 4.6: The moraine dam of Laguna Safuna Alta. Note the flood wave scar, rising from left to right.

Fig. 4.7: Eroded moraine dam.

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4.6.2.2 Terminal moraine As described briefly previously there are several sets of terminal moraines the lowermost of which effectively dams Safuna Baja while the largest dams Safuna Alta. The lowermost terminal moraine (Figure 4.8) is hummocky, very well vegetated and is used for grazing by cattle. Its freeboard above the level of Safuna Baja is of the order of 10 m. While former glacial outlet channels can be identified, they are all stranded at levels well above the current lake surface.

Fig. 4.8: Laguna Safuna Baja, showing the approximate position of the sub-aqueous moraine ridge. The low hummocky moraine dam is in the upper part of the image. Within the terminal moraine of Safuna Baja there is evidence of a smaller moraine ridge (Figure 4.8) whose surface gradient is far steeper than either of the two contemporary moraines. At lake level within Safuna Baja, the moraine ridge can be traced sporadically across the lake with the furthest extent of the moraine and hence former glacier being on the right hand side of the lake. The main terminal moraine is that which dams Laguna Safuna Alta. It rises approximately 80 m above the present lake level at its lowest point, reaching to over 100 m at its maximum. The morphology of the terminal moraine has been radically altered during the 22nd of April event by the

effects of at least one displacement wave overtopping the moraine (Figures 4.5, 4.7 and 4.9). The proximal side of the terminal moraine (Figures 4.5, 4.7 and 4.10) show the effects of the displacement waves extremely clearly. The scar associated with the maximum water level is well highlighted by its light colour tone (Figures 4.5, 4.6 and 4.7) and has an increasing elevation above the lake level with distance away from the southern end of the lake where the landslide entered the water. The proximal flank has been seriously eroded by the waves, leaving in one location a very over-steepened part of the proximal flank of the moraine, just west of the 1978 tunnel portal. In this part the displacement wave clearly overtopped the moraine and caused major damage. To the east of the 1978 tunnel portal, at least one displacement wave overtopped the terminal moraine. What appear to be strandlines formed by the maximum run-up of subsequent (seiche) waves occur at a variety of heights above the present lake level (Figures 4.7 and 4.10). Undercutting of the toe of the proximal flank has also occurred as can be seen in Figure 4.10. The distal flank of the terminal moraine shows two key areas where the displacement waves have stripped the slope of its vegetation and in places much of the surface layers of sediment. The swathe affected by the first and largest wave can be seen in Figure 4.9. There are a few tracts of vegetation still intact where the flood wave diverged around obstacles protecting these areas. The western part of the distal side of the terminal moraine has also undergone further massive erosion and down cutting arising from further overtopping of the moraine by subsequent seiche waves and/or by the flow of water through the 1978 tunnel while the water level in Laguna Safuna Alta was elevated during or following the landslide event. A debris fan can be identified easily on the right of Figure 4.9 (edges marked by dashed lines). The sequence of events of the 22nd of April 2002 is discussed in Section 4.7.

Fig. 4.9: Distal side of the Laguna Safuna Alta moraine dam.

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Fig. 4.10: Proximal side of the Laguna Safuna Alta moraine dam. Numbers 1-10 are the interpreted limits reached by successive waves. Carcasses of cattle killed in the flood are located on and within the debris fan at the western side of the upstream shoreline of Safuna Baja and one isolated and highly disfigured carcass was found on the eastern side. Parts of the distal flank of the moraine have also undergone slope failures after the main displacement wave overtopped the terminal moraine. Shallow debris flows mobilised circular areas of sediment (highlighted on Figure 4.9). It is clear from remnants of undamaged vegetation just at the distal edge of parts of the ridge crest of the terminal moraine that the highest displacement wave became airborne as it passed over the ridge. Damage below these areas was severe and indicated that the impact of the wave bit into the hill slope and gouged out whole areas of the moraine flank. 4.6.2.3 Moraine stability The distal side of the moraine ridge commonly stands at between 36o and 40o, although angles ranging from 22o to 50o were also measured. The proximal side, however, tended to be much steeper with angles from 40o to 72o being measured and the most common range being between 50o and 56o. Local stonefall occurred frequently from the inner face, suggesting that these steeper angles are not sustainable. The inner face was free from vegetation throughout. As discussed, one of the few areas of surviving vegetation on the outer face, is below the low point of the ridge. The zone below the surviving vegetation is the least steep part of the outer slope, with angles between 22o and 28o. Opposite the eastern end of this area is a very steep (68o) gully in the proximal face. There is extensive cracking on either side of this gully and the crest in this area appears to be highly unstable. Cracking was seen elsewhere at intervals along the crest.

A well-defined deep gully has been eroded in the outer face of the moraine dam immediately below the second tunnel (Figure 4.11). It appears to have been formed very recently and it is assumed to be related to the recent landslip and flood. The gully extends to the lower part of the slope where it meets the broad gully that defines the western edge of the slope. This latter gully is the mouth of the ablation valley between the two most recent moraine ridges. Fresh erosion and some huge reworked boulders provide evidence that this gully has been exploited by the recent flood. A shallower gully exists in the upper part of the distal face of the moraine dam, above and below the portal of the second tunnel and running into the deeper gully in the lower part of the face. Examination of the materials that have been exposed by the removal of the vegetation and especially of the materials exposed in the gullies indicates that these parts of the moraine consist generally of silty gravelly sand with many cobbles and some boulders. Little cohesive material was noted. It may be significant that, in parts of the exposure in the walls of the gullies, a thin layer of rounded cobbles was visible a short distance below the surface. This material did not appear to be present on much of the slope and it was considered possible that this layer was removed with the vegetation by the overtopping wave.

Fig. 4.11: The distal face of the moraine dam showing a deep erosion gully below the 1978 tunnel. The innermost terminal moraine is continuous with lateral moraines to either side. These are vegetated on their distal sides, more sparsely on the right lateral than the left, and are devoid of vegetation on their proximal sides. On both sides of the valley, the inner lateral moraines rest against older lateral moraine ridges. The termo-lateral moraines damming the lower lake are now degraded but remain up to 60 m high on their distal side and are well vegetated. Slope angles between 20o and 36o have been measured on the outer flank of the terminal moraine. The inner flank of the terminal moraine is now ill-defined but the inner

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flanks of the associated lateral moraines stand at between 34o and 42o whereas angles between 30o and 40o have been measured on their outer flanks. 4.6.3 The tunnels The younger tunnel suffered damage as a result of the landslide and subsequent displacement wave. At the distal end, the spillway structure was completely destroyed and a deep erosion gully was in its place (Figure 4.12). At the time of the fieldwork, the distal portal was intact, as was the interior of the tunnel over almost its whole length. It contained no morainic debris. The interior of the tunnel was almost completely undamaged to the extent that the cast of the wooden formwork remains visible, including the grain of the wood. At one point a small fragment of that wooden formwork remained loosely attached to the roof. The proximal portal was both exposed and damaged (Figure 4.13). It protruded some 2 m from the moraine and was undercut below. The morainic materials formed an arch above the protruding tunnel with the material from beneath the arch removed. There was relatively minor damage to the concrete at both the crown and the plinth of the tunnel.

Fig. 4.12: Distal portal of the 1978 tunnel showing minor damage.

The older tunnel was difficult to access and was visited only once on 8th August 2002, by DQ and APH. Major damage was visible at the distal portal. Only a short length of spillway remained immediately below the portal. The spillway bed was seen to consist of cemented masonry blocks with low concrete bounding walls. At the portal the western wing wall had toppled inwards (Figure 4.3) and was leaning diagonally across the entrance and resting largely in one piece on the eastern wing wall. However, the interior of this tunnel was largely undamaged almost to the proximal portal. At the proximal portal the first two tunnel sections were destroyed, with only the substantial ribs remaining. The third section, now flush with the face of the moraine, was largely intact but dislocated from the fourth section. There was a gap approximately 0.3 m wide and a small angular distortion between these two sections. A mound of morainic material existed beneath the gap between these sections. In contrast to the 1978 tunnel, the floor of the 1970 tunnel contained a layer of debris approximately 0.3 m deep throughout its length (except at the mound described above). The debris was fine to coarse, sub-rounded morainic material ranging from sand to cobble or small boulder size.

Fig. 4.13: Proximal portal of the 1978 tunnel showing significant damage. Note that the tunnel is undercut below and exposed above with arching of sediment. 4.6.4 Rock slopes The exposed rock slopes on the western valley side were seen to consist largely of slightly weathered thinly to thickly bedded quartzite. For the most part the bedding was sub-vertical striking parallel to the long axis of the valley (approximately 145o). Locations were seen where the dip of the bedding was steeply to the west (Figure 4.14) and others where it was steeply to the east (Figure 4.15). A similar situation was seen to continue to the other side of the mountain ridge and into the Pucacocha valley showing a consistency of structure for some

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distance. It is understood that mudstones, sandstones and anthracite bands are normally found in this geological unit, but the strata seen in the accessible areas appeared to consist very largely of quartzite. Some fragments of coal were found within the debris at the toe of the landslide and it seems likely that these correspond with some thin dark coloured bands in the face of the landslide.

Fig. 4.14: Safuna Glacier with rock outcrop showing steeply westward dipping discontinuities. Examination of the rocks that remain in situ at the toe of the landslide, exposed at its northern end but visible only from across the lake, indicates the bedding to be sub-vertical and in places to be overhanging, i.e. dipping very steeply to the west. However, in the upper part of this exposure, the bedding is much more severely overhanging i.e. dipping less steeply to the west (Figure 4.16). Similarly, looking at the upper part of the slip (Figure 4.17) the strata are again severely overhanging. The northern edge and crest of the slip were visited by BH and APH on the 5th of August 2002. Slightly weathered quartzite was visible at the outcrop in places adjacent to the failure, but elsewhere there was a covering of highly weathered material or of colluvium. Extensive tension cracking was seen in all of these materials. These tension cracks ranged from 75 mm to 2 m in width and the larger ones could be seen to be a minimum of 6 m deep (Figure 4.18). In places the tension cracks exploited the bedding in the rock, but elsewhere cracks could be seen cutting indiscriminately across the bedding (Figure 4.19). The tension cracks occurred in a zone up to 100 or 150 m to the rear of the crest of the slip in the area to the north of the centre of the slip at an altitude close to 4,700 m.

Fig. 4.15: Outcrop of quartzite adjacent to the landslide, showing steeply eastward dipping discontinuities.

Fig. 4.16: Lower part of the cliff from which the landslide failed, showing steeply westward dipping discontinuities and flexural toppling. The backscarp of the slip was complex involving many parallel tension cracks and horst and graben features. At an altitude close to 4,720 m in the north, rising to 4,745 m in the centre, a major backscarp was located. This had a throw of 5-6 m and marked the rear of this highly disturbed area. Some smaller subsidiary tension cracks were seen to the rear of this to an altitude of around 4,800 m.

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Fig. 4.17: Upper part of the landslide with westward dipping discontinuities in the backscarp.

Fig. 4.18: Tension cracks to the north-west of the landslide face.

Fig. 4.19: Tension cracks exploiting bedding (blue arrow), but also cutting across discontinuities (red arrows).

4.6.5 Safuna Glacier Prior to the landslide of 22nd April, the snout of Safuna Glacier terminated at or near the southern shore of Safuna Alta. The landslide covered the snout that remains obscured by the debris (Figure 4.20). The glacier is fed by snow- and ice-avalanches from the mountains behind in addition to any snow accumulation during the mass balance year. The eastern part of the glacier is more heavily debris-charged than the western side, largely due to the inputs from the serac field associated with a small glacier on the eastern flank of the valley (Figure 4.4). The glacier shows prominent longitudinal foliation, especially associated with the medial margin between the two flow units that make up the glacier (Figure 4.20). The cleaner part of the glacier is fed by an icefall below Pucajirca Oeste. The western side of the glacier is in direct contact with the steep rock wall upstream of the April landslide. It would appear that the glacier is providing support for this rock mass.

Fig. 4.20: Safuna Glacier and landslide. The eastern flank of the glacier is vertical (Figure 4.20) and has a serrated appearance arising from the ablation of emergent structures from the glacier (Figure 4.21). No ponding of water was observed along this flank with all melt water draining down into the ground moraine towards Laguna Safuna Alta.

Fig. 4.21: The eastern flank of Safuna Glacier.

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A thin medial moraine lies on the surface of the glacier (Figure 4.20). A small amount of supra-glacial drainage was observed just upstream of where the landslide covered the snout, but there was no significant ponding of water anywhere to be seen. All melt water drained off or through the glacier. The upstream boundary of the landslide on top of the glacier was very clear to see (Figure 4.22) with a debris cover of at least 10 m over the medial moraine with considerably thicker cover on the western flank closest to the landslide fan on the western side. Where the landslide had completely crossed the glacier, the thickness of debris there was estimated to be in excess of 40 m thick. 4.6.6 Hydrology At the time of the field visit the upper lake stood at a level close to 4,354.6 m. It is fed by a stream descending from the lowest visible part of the glacier and flowing under the rock wall that bounds the eastern side of the glacier, where it is supplemented by a waterfall passing over the cliff, before entering the south-eastern corner of the lake. Given that there was no blockage to the drainage of melt water and no subsequent ponding upstream of the landslide, it is concluded that the coarseness of the landslide debris permits intra-formational flow of water through the landslide and into Safuna Alta below the current water line. No springs were seen on the landslide debris upstream of the lake. Two further streams enter the lake slightly north of its south-eastern corner. Both of these drain from glaciers high above on the east and flow and fall over rocks before reaching the right lateral moraine. Both have eroded major gullies in the moraine as they descend to the lake. Occasional small areas of seepage were visible on the lower inner flank of the moraine. There is no visible outflow from the lake but a line of springs rise across the full width of the outer flank of the terminal moraine a short distance above its base.

These springs flow into the lower lake. Seepages were also noted along the lower part of the proximal flank of the right lateral moraine bounding Laguna Safuna Baja adjacent to the distal side of the terminal moraine of Laguna Safuna Alta. The lower lake has a strand line and it is clear that its level varies seasonally. The level given on the INRENA topographic survey is 4274.4 m. A discharge portal from Safuna Baja was located on the left shoreline, and has been mapped by INRENA. No other discharge outlets were observed. Drainage occurs through the ground moraine, where major springs rise at the foot of the lower moraine towards its eastern side. These can be seen flowing out of the base of the moraine but also bubbling up in the base of pools at the south-eastern edge of the meadow close to the toe of the moraine. If this is the same water that is seen to sink on the western side of Laguna Safuna Baja, it is notable that the flow crosses the valley floor. From the springs and pools, the streams rapidly coalesce to form a large stream that joins the stream coming from the Pucacocha valley to flow down Q. Tayapampa. 4.7 The landslide of 22nd April 2002 4.7.1 Summary of the April 2002 event It is clear that a major landslide occurred from the western flank of the Safuna valley on 22nd April 2002. The dimensions of the scar may be estimated at approximately 400 m high, 400-500 m wide and 100-150 m deep. The estimate of depth is particularly inexact since the shape of the slope prior to the slide is not known. These dimensions indicate that the volume of the slide may have been 9-15 x 106 m3. These figures relate to a failed mass of rock of 24-40 x 106 Tonnes. As there were no observers, it is not known if the slope failed as a unit or piecemeal over a period of time, nor is it especially relevant in assessing the risk. However, it is clear from the scale of the effects that at least one major event must have occurred.

Fig. 4.22: View down Safuna Glacier. The figure (circled) marks the boundary between the medial moraine and the landslide debris.

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From the evidence that remains in and adjacent to the landslide scar, it seems more than likely that the mechanism of failure was flexural toppling and, in places, block flexural toppling, where the former may be defined as failure by the bending forward and fracture of continuous columns of rock separated by well developed steeply dipping discontinuities. In the mechanism of block flexural toppling, failure occurs where the long columns are divided by numerous cross joints, as a result of accumulated small displacements on the cross joints rather than by flexural failure of the long columns. It is clear that part of the debris resulting from the landslide fell into Laguna Safuna Alta and part of it fell onto the tongue of the Safuna Glacier. The part that fell onto the glacier can be seen as a tongue of debris crossing the full width of, and obscuring, the glacier (Figure 4.20). The part that fell into the lake is not visible but the bathymetric survey shows that the volume of the lake decreased by 6.4 x 106 m3 between 2001 and August 2002, presumably as a result of the landslide. This figure lends some credibility to the estimates given above for the volume of the landslide. 4.7.2 Lake and seiche waves It is clear that the impact of the landslide created an initial displacement wave of 80 m to over 100 m in height, which overtopped the terminal moraine dam, and its debris decreased the depth of the lake by 40 m. Details of the infilling of the lake have been provided above. Given the obvious magnitude of the impact of the landslide into the lake, there must have been a sequence of waves following the initial displacement wave arising out of the flowing backwards and forwards of the water within the lake basin. Such oscillating waves are known as ‘seiche’ waves. The height of the run-up of each successive seiche wave on the proximal side of the terminal moraine dam would have decreased but each is likely to have formed a maximum watermark on the proximal moraine flank (Figures 4.7 and 4.10). There would also have been corresponding but lesser run-up distances associated with the reverse waves travelling upstream and impacting upon the landslide debris above the lake waterline. Indeed, stranded vegetation had formed what appeared like old shorelines at heights of several tens of metres on the landslide front, with backscarps associated with the attrition of the landslide by the reverse seiche waves impacting upon it. It is not possible to identify the strandlines associated with each progressive seiche wave, but an indication as to the run-up heights, especially on the proximal side of the terminal moraine of Safuna Alta can be obtained (Figure 4.10). It is suggested from evidence of damage after the first displacement waves overtopped the moraine that a second wave may

have just reached the ridge crest (80 m to 100 m) allowing water to overtop a second time in a few places but with much less damage that from the first wave, and then with progressively smaller volumes, the third and fourth waves would have overtopped only the lower parts of the terminal moraine (Figure 4.10) progressively towards the west. It is suggested that the second overtopping wave may literally have contributed just enough water to initiate debris flows of very limited extent on the distal side of the moraine (such as those indicated in Figure 4.9), with some of the debris flows failing to reach even Laguna Safuna Baja. Judging from the distribution of strand lines from the seiche waves it would appear that the waves impacted initially on the moraine near the 1978 tunnel then ran-up the eastern side of the moraine causing the wave top to increase its height. It is thought that the maximum run-up heights on the eastern side of the lake were up to 20 m higher than those near to the 1978 tunnel part of the moraine. A series of at least ten strandlines has been identified (Figure 4.10) with each successive limit being lower in elevation than the one before. The primary displacement wave overtopped the terminal moraine with such impact that it created a secondary displacement wave within Safuna Baja with an amplitude of up to ~2.5 m on the downstream shoreline. The splash zone associated with this wave can be seen in Figure 4.9 where the wave entered the lower lake on its western edge. At least 22 cattle were drowned near the lower lake as a result of this event (Figure 23).

Fig. 4.23: Cattle carcasses on the shore of Laguna Safuna Baja. 4.7.3 Moraine and tunnels In addition to the formation of strandlines associated with the seiche waves, the various waves caused significant damage to the moraine. The interpreted events pertaining to the distal side of the moraine will be described first, then those affecting the proximal side.

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It is clear from observations of the distal side of the terminal moraine that the greatest and most immediate damage was caused by the first wave that overtopped the terminal moraine. The impact of this wave gouged out whole areas of the moraine that failed along discrete interfaces between layers with different material characteristics. It is apparent that the moraine structure comprised a series of parallel and/or sub-parallel layers dipping downstream (Figure 4.24). Failure appears to have occurred along a plane comprising coarser material than that either above or below it and located approximately 1 m below the former moraine surface. In some places, the impact of the wave was sufficiently large that erosion of material deeper than this occurred. Material eroded from higher up the slope was deposited on the lower shallower gradient parts of the moraine flank.

Fig. 4.24: Weak stratification in the Laguna Safuna Alta moraine dame, dipping downstream There were several flows that occurred arising from the subsequent seiche waves overtopping the moraine. These appeared to have eroded material within very localised limits and run-out distances were very small, barely reaching Laguna Safuna Baja in places. While these minor overtopping debris flows occurred along the eastern part of the terminal moraine, the elevated water level within Laguna Safuna Alta also contributed to flow through the two concrete-lined tunnels. Flow through the 1970 tunnel caused little damage to the tunnel. The discharge portal spillway remained intact and allowed the water draining through this tunnel to be discharged without causing any erosion until it reached the end of the spillway (Figure 4.9). However, the lower, 1978, tunnel was able to provide drainage for longer. One difference here, however, was that there was no deposition of debris within this tunnel. The concrete spillway at the discharge end of the 1978 tunnel were both completely destroyed and massive erosion took place in this area, resulting in the discharge portal almost becoming suspended over the eroded area.

However, the distal flank of the moraine above the 1978 tunnel portal was also heavily eroded and it is suggested that the area was affected by up to a further three overtopping waves that focussed on this part of the moraine. The erosion and debris fan associated with this area clearly cross cut the flows and channels formed by the debris flows from further east along the moraine, as indicated in Figure 4.9. This suggests that water continued to flow through this area well after flows had ceased overtopping further east along the terminal moraine. Erosion in the area above the tunnel may have been further facilitated by loosening of the ground above the tunnel during its construction. If the interpretation of the position of strandlines from seiche waves is correct, then the area of the 1978 tunnel could have experienced a total of four overtopping waves. These overtopping waves would account for the large amount of erosion above the tunnel discharge portal (Figure 4.25). Laguna Safuna Alta would have been at an elevated level, due to displacement by the rock avalanche debris, until the 1978 tunnel (and seepage) was able to reduce the volume. Prolonged drainage of relatively sediment free displaced water could also account for the lack of damage to the discharge portal channel with only minor gouges from impacting boulders being observed on the channel floor. It is possible that the high-pressure flow through the tunnel kept debris out of the channel until the flow had virtually ceased and debris was able to bounce onto the concrete floor. It may also be significant that, although there is deep erosion both above and below the tunnel, there is rather less at the actual level of the tunnel. This suggests that the tunnel may have acted as structural member, reinforcing the dam.

Fig. 4.25: Exit portal of the 1978 tunnel. The erosive effect of the wave(s) on the moraine can be seen in a line rising across the inner face of the western lateral moraine (Figure 4.26). It is clear that the event has caused some erosion of the inner face of the moraine dam as a whole. The 1978 tunnel now protrudes 2 m from this face and is undercut by a similar amount. Thus, it seems certain that around 2 m of material has been scoured from the face of the

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moraine at this point. The amount of erosion does not appear to be uniform, for example, above this tunnel the morainic material arches with greater erosion immediately above the tunnel presumably because this material is looser due to stress relief caused by the tunnel operation. A short distance west of this tunnel is a deeply eroded and steep erosion gully that appears more defined than on older plans (Figure 4.27). It seems likely that this gully was eroded by the displacement wave(s) that resulted from the landslide.

Fig. 4.26: Left lateral moraine showing the line of fresh erosion (arrowed) from the displacement wave after the 22nd April 2002 landslide.

Fig. 4.27: Steep gully in the proximal face of the moraine. As discussed, the portals of the 1978 tunnel were both damaged. The proximal portal was undercut, its crown exposed and the structure has suffered minor damage. The distal portal suffered minor damage too and the spillway was completely destroyed. However, the main part of the tunnel was undamaged. Neither did it contain any solid debris, nor was there any evidence that solid debris had ever passed through it. It may be speculated that, at the moment of impact of the displacement wave(s), when the water would have been laden with debris, little of the water passed through the tunnel, most

passing over the top of the dam. Once the initial wave had passed, it seems certain that the excess water in the lake, now cleaner because the sediment had to some extent settled, was dissipated by way of the tunnel, leaving the tunnel clean but causing considerable erosion below the portal. The 1970 tunnel was also damaged at both portals, with the toppled wing wall and truncated spillway at the distal end and the exposed ribs of reinforcement at the proximal end. There was also some dislocation of tunnel sections close to the proximal portal. It has been assumed, partly from its degenerated and rusted appearance, especially at the proximal end, that this is old damage resulting from the 1970 earthquake. In contrast to the 1978 tunnel, a layer of debris covered the base of the tunnel along its full length. It may be that, being at a higher elevation, the only water that was dissipated by this tunnel was in the early stages of the event, while it was still heavily sediment charged, and that it was not subsequently flushed clean by sediment-free water. Alternatively, it may be that the fallen wing wall, so obstructed flow at the distal portal that sediment was deposited in a way that did not occur in the 1978 tunnel. A further alternative may be that the debris was already in the tunnel, as a result of 1970 earthquake damage, but perhaps stacked beneath the dislocation near the proximal portal. Water from the 2002 landslide then redistributed the debris along the full length but either because at this high level the event was too short lived or because of loss of power due to partial blockage by the toppled wing wall, the redistribution stopped short of flushing the tunnel clean. 4.7.4 Lower lake As described above, the impact of the landslide event on Laguna Safuna Baja appeared to be limited to the inflow of the main overtopping wave followed by the minor impacts associated with subsequent overtopping along the main part of the moraine. Of greater significance was the more prolonged inflow of water from the western part of the moraine over the terminal moraine and through the tunnel. However, the lake level in Safuna Baja rose only by ~2.5 m and this was thought to have been due to a secondary displacement wave arising from the inflow of the initial overtopping flood. There was no evidence found to suggest a series of seiche waves in Laguna Safuna Baja. It is thought there was the one initial wave that drowned the cattle. Damage around the lake was limited to vegetation broken and sediment stranded by the initial wave.

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4.8 Hazard assessment 4.8.1 Moraine Dam The steady state stability of the moraine dam has been examined by constructing cross sections through the dam at two points, one through the steep gully in the proximal face and the second close to the 1978 tunnel and including the erosion gully below the distal portal. As may be expected, the first of these proved the more critical and is the one discussed here. It must be emphasised that the discussion that follows relates to the steady state stability of the dam and does not take into account the effect of any external influences such as displacement waves or seismic activity. The cross-section was constructed from information supplied by INRENA from their topographical survey of August 2002. The water level was estimated from the known steady state level of the lake and the observed level of springs on the downstream side. For the purposes of the analysis the moraine dam was treated as a single material type the parameters of which were estimated by comparison with similar materials from Nepal and elsewhere. A unit weight of 21 kNm-3 was selected, together with an effective cohesion of 5 kNm-2 and an angle of internal friction of 38o. Analysis was carried out using the software package SLOPE/W for circular slip surfaces, the analysis method of Janbu proving the most critical.

The analysis showed that the minimum factor of safety against a small failure on the proximal face is 0.66 (Figure 4.28) and that against a large failure on the same face is 0.75 (Figure 4.29). Both of these predict failure. The minimum factor of safety calculated against a small failure on the distal slope is 0.94 (Figure 4.30) whereas that against a major failure is 1.47 (Figure 4.31). The former predicts failure whereas the latter figure does not and is approaching the type of safety margin that might be considered adequate. It is not unexpected that small failures are predicted on the outer, and especially the inner, slopes since these were observed in the field. Neither is it surprising that a major failure is not expected on the outer slope. The clear prediction that the inner slope is so far from being stable in relation to a major failure is perhaps unexpected and it may be that the parameters used were too pessimistic. For this reason a back analysis was performed to find what parameters of c’ and ø’ would be required for the analysis to result in a factor of safety of unity, i.e. the minimum required to predict even marginal stability. Two alternative results were obtained, either c’ =15 kNm-2, ø’ = 45o or c’ = 10 kNm-2, ø’ = 48.5o. Both these results are exceptionally high and it would seem unwise to rely on such parameters as a minimum for even marginal stability. It is clear that even considering the steady state, the moraine dam cannot be considered stable. If a further displacement wave were to occur then the stability of the dam is still more questionable.

Fig. 4.28: Slope analysis showing factor of safety against a small failure in the proximal gully.

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Fig. 4.29: Slope analysis showing factor of safety against a significant failure in the proximal gully.

Fig. 4.30: Slope analysis showing factor of safety against a small failure in the distal face.

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Fig. 4.31: Slope analysis showing factor of safety against a significant failure in the distal face. 4.8.2 Trigger mechanisms Events that are likely to trigger displacement waves or other external influences on the stability of the moraine dam include rockfall, ice avalanche and seismic activity. Examination of the slope adjacent to the rockfall of 22nd April 2002 reveals a large number of apparently active backscarps and tension cracks. There can be little doubt that the scope exists for a further large scale failure. The size of such a failure is unlikely to be as large as that of 22nd April 2002, but it may be a half to one third as large. This could still involve around 5 x106m3 or 10-20 x106 Tonnes of rock. It may be considered that if the dam and lower lake could resist and contain the 2002 event then they will also contain a smaller event. However, it may be that the dam is now weaker and that the next event may be closer to it and that more of the debris will fall into the lake. The stability analyses show that the moraine dam can hardly be expected to resist such an event. The rock slope on the eastern side of the lake appears to be much more stable on the large scale. The rock material appears to be more competent and the jointing pattern less regular with fewer persistent discontinuities. There is no doubt that rockfall will occur but it is likely to involve isolated blocks of small or moderate size that may or may not reach the lake.

Assuming that the glacier continues to retreat, it will at some stage cease to provide lateral support to the rock slopes to either side and particularly to its west. The main discontinuity set in this latter area dips steeply to the west and the slope is therefore susceptible to toppling failure. Loss of lateral support is likely to promote such instability. However, the site of this face is currently remote from the lake and, being set at a higher level, it seems that, even with melting of the glacier, the lake is unlikely to extend this far in the foreseeable future. Given the apparent permeability of the landslide debris, it is unlikely that meltwater will pond behind the landslide. Thus, in the foreseeable future, it seems unlikely that rockfall in this area will reach the lake and cause a displacement wave that can threaten the moraine dam. Should the permeability of the landslide dam decrease so that ponding of melt water does occur then as the glacier continues to retreat up-valley, there may eventually develop a risk of ice avalanching into another higher lake. However, such behaviour would be identified easily by use of high-resolution satellite images or from field observations in any monitoring programme. Consequently, the hazards associated with Safuna glacier are small at present but may gradually increase with time, but are still likely to remain far less of a hazard than the unstable rock slopes along the left margin of Laguna Safuna Alta. In addition to rock faces, the lake is flanked on three sides by unconsolidated morainic materials.

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Instability in these materials is to be expected and indeed is observed from time to time. However, because of the essentially granular nature of the moraine, those failures that occur, or would be expected to occur, are relatively small scale, though frequent. As such, the risk of a failure of the morainic material resulting in a major displacement wave is considered to be small. Given that the glacier snout is now buried beneath the landslide debris there is no hazard arising from the glacier at present in relation to the stability of the lake or moraine. The only source of ice avalanche material could come from the west facing serac field of the glacier terminating above the rock cliffs that form the right margin to Safuna Glacier (Figures 4.21 and 4.32).

Fig. 4.32: Serac field at the snout of a local glacier north of Safuna Glacier. 4.9 Potential vulnerability 4.9.1 Tourism and Visitors During the field visit, tourists were seen every day in the Safuna valley or Quebrada Tayapampa just below. Many of these were day visitors from Pomabamba but some, both local people and visitors from elsewhere in Peru and from abroad, were given to camping in the base of the Quebrada Tayapampa above the houses of Huillca. The upper valley and the area below Huillca are popular with fishermen who, self-evidently, spend their time beside the rivers and lakes, often in the valley bottom. Should a catastrophic failure of the lake occur all these people must be considered vulnerable. Occasional visits by scientists or members of INRENA staff or others, to study the lakes and their surroundings are not without risk and should also be included in this list.

4.9.2 Habitation The nearest habitation to the Safuna lakes is the few houses of Huillca some 5 km downstream and 350 m lower than Laguna Safuna Alta. The houses stand on a flat area beside the main river and they and their inhabitants must be considered vulnerable to a major flood. Other settlements beside the river at greater distances along the Q. Collota to and beyond the village of Quitaracsa must also be considered at risk. Quitaracsa is 24 km below Safuna but it is unlikely that, with the current infrastructure, there would be significant warning to its inhabitants of an approaching flood. The valley is relatively broad immediately below Huillca and it may be that some of the energy of a flood would be lost in this section. However, lower down the valley narrows again and a flood may be expected to become more focussed. The Rio Quitaracsa, into which the flood would be channelled, joins the Rio Santa 40 km downstream from Safuna and the possibility that a destructive flood would continue into the valley of the Rio Santa cannot be ruled out. The first sizeable village is Huallanca, 1 km below the confluence, and this is said to house many of the workers from the Cañón del Pato power station. Although this area was not examined during the field visit, it should be considered vulnerable pending further investigation. 4.9.3 Huallanca Hydro-electric Project The Huallanca HEP was not visited during the field season but, from the topographic map, it appears that some buildings and other installations are at the confluence of the Rio Quitaracsa and the Rio Santa. All these must be considered to be at risk. It is understood that further installations of the power station are located a short distance upstream in the narrow Cañón del Pato of the Rio Santa (Figure 4.33). There is the definite possibility that a catastrophic flood, emerging from the Rio Quitaracsa laden with debris, would cause a blockage at the foot of the Cañón del Pato and that the Rio Santa may back up causing further severe damage upstream of the confluence. Clearly, subsequent breaching of such a blockage would result in more damage downstream. 4.9.4 Landuse In addition to the habitation downstream of Safuna, the land is agriculturally valuable, chiefly used for grazing for sheep, cattle, horses and camellids. There are also small cultivated plots adjacent to the villages. It is likely that some or all of this land would be seriously damaged and lose its function as a result of a flood following failure of the moraine dam.

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Fig. 4.33: Spillway at the Cañon del Pato water intake. 4.10 Risk management 4.10.1 Lake security measures It appears that the tunnels performed a valuable function in dissipating excess head of water after the landslide. It would be worthwhile and relatively straightforward to repair the tunnels and restore their function. Should it be necessary to prioritise then it would be both more valuable and easier to repair the 1978 tunnel than the 1970 tunnel. In the case of the 1978 tunnel, it is necessary to make repairs to both portals, especially to make safe their undercut condition and, at the proximal end, to protect the exposed steel reinforcing members from corrosion. At the distal end, the spillway structure would need to be reconstructed to avoid catastrophic erosion of the gully below the tunnel should a further event occur. In relation to the 1970 tunnel, the portals would need to be repaired, including cutting off and reconstructing the proximal portal and replacing the wing wall at the distal portal and reconstructing the spillway. The tunnel would need to be cleaned out and the dislocation near the proximal end repaired. In view of the more serious nature of these repairs and the more difficult access compared to the 1978 tunnel, it may be considered more cost-effective rather than to repair the 1970 tunnel, to increase the capacity for dissipation by constructing a new tunnel at or below the level of the 1978 tunnel. Although the tunnels have worked well in the past, it must be recognised that they do not serve to prevent a catastrophic failure of the moraine dam at the moment of impact of a displacement wave, only to reduce the likelihood of subsequent failure due to excess head of water. In order to reduce the susceptibility of initial catastrophic failure, it would be necessary to either remove or limit the trigger, reduce

or remove the water in the lake or strengthen the moraine dam. Works to mitigate the trigger are not practical due to the size of the potential landslide and its inaccessibility. It would, no doubt, be possible to cause the landslide to occur, perhaps in the hope that it will take place in small stages, and to do this at a time when the valley below is evacuated. However, the difficulty of predicting the likely result and evacuating the whole area of both people and livestock mean that this course of action is most inadvisable. Even if the population are protected, damage to land, habitation and installations such as the HEP project are likely to be irreparable. Reduction of the water level in the lake is likely to prove extremely difficult. Since there is currently at least 80 m of freeboard, an open cut to and below the existing water level would be a very major work indeed and probably very hazardous. It may prove possible to construct a tunnel below the water level and thereby reduce the amount of water in the lake, but although the technology exists, it has not been tried under circumstances like these. To drive a tunnel through unconsolidated moraine below the water table would require techniques aimed at excluding water from the heading. It may prove possible to do this by grouting or freezing forward of the heading. It may be possible to drive a much longer tunnel, chiefly through the bedrock that flanks the valley on either side, but at both portals it would be necessary for such a tunnel to pass through unconsolidated moraine or colluvium. By careful selection of gradient of such a tunnel it may be possible to pass through the unconsolidated material at the distal portal at a level above the water table, yet still enter the lake at a useful level below the water surface. Self evidently, the unconsolidated material at the proximal portal must be below the water table but it may be possible to choose a location where this is thin. Due to the exposure of rock close to the lake surface on its western side, it may be considered that this is the preferred side for such a tunnel. However, it should be borne in mind that the rock on this side contains far more discontinuities than on the eastern side and that this would have an effect on the ease of tunnelling. There is also the possibility that tunnelling works may precipitate a further landslide. A further option would be to carry out works to strengthen the dam, either locally in areas identified as weak or across the full width of the dam. It seems unlikely that this could be achieved by facing the dam or by the provision of reinforcing elements. Rather, it seems, that the method most likely to be effective would be to strengthen the dam by injection of grout or other cementitious materials. Calculation of the

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amount of strengthening necessary relies upon a large number of unknowns, including the size of event to be resisted. In this location, any of these possible works would be extremely difficult logistically. It should also be borne in mind that during such works, there is the ever present danger that a catastrophic event will occur. Even if it is possible to execute the works in such a way to avoid precipitating an event, there remains the possibility that an event will occur while construction workers are present and in that case it is to be expected that the consequences would be disastrous. 4.10.2 Monitoring Given the status of Laguna Safuna Alta and the high probability of another large landslide into the lake, and only a minor risk arising from the local glaciers, it is recommended that the area should be monitored on a regular basis. High-resolution satellite imagery could be used, although this is relatively expensive and does not have the resolution to detect changes in tension cracks or similar small features. It is recommended that a walkover survey is carried out at frequent intervals, perhaps twice per year, by staff competent at assessing any deterioration in the condition of either the moraine dam or the triggers. Photographs of key aspects of the area could be repeated during each visit and changes identified. Given the relative ease of access to this site, such a suggestion is not overly complex and need not be particularly expensive and could be undertaken using INRENA staff. Changes in the size and surface elevation of the lakes should also be monitored and fully surveyed at less frequent intervals. It would be possible to instrument the landslide and adjacent areas, perhaps using extensometers, in order to provide precise information on small movements and particularly on any acceleration of such movement. This information, together with that from the site visits, could be sent by radio to Huaraz and linked to an evacuation and disaster preparedness strategy for villages and the Huallanca HEP. As discussed in Section 4.9.1, it must be recognised that any persons installing instrumentation or carrying out monitoring, or even performing the walkover, are at risk. It would therefore be necessary to expose the minimum number of people for the shortest period of time and to make these people aware of the risks. Both to minimise such risks and to provide an early warning system, it would be significantly advantageous if any instrumentation could be monitored remotely.

4.10.3 Vulnerability The vulnerability to the hazard could be reduced somewhat by disseminating information about the risk. If local schools are informed then it may be that they will terminate group excursions to this valley. Assuming that there are other valleys that would provide a similar educational experience, then this would seem to be a wise precaution. Similarly, the provision of posters with information about the risk, would allow fishermen and tourists, both local and otherwise, to make an informed decision about their visit. As discussed above, visits by scientific and technical staff must be recognised as containing an element of risk and carried out accordingly. The vulnerability of permanent residents, infrastructure and installations is much more difficult to address. It is unlikely that the whole area can be permanently evacuated, not least because of the uncertainty regarding the area that could be affected. Supply of information to residents in the upper valley would allow them to make an informed decision. Discussion of the feasibility of protective measures to the power station and the larger communities downstream is outside the scope of this report since these areas were not visited during the fieldwork. 4.11 Conclusions and recommendations The massive landslide that fell into Safuna Alta on the 22nd of April 2002 resulted in the terminal moraine dam being badly damaged by a series of displacement and subsequent seiche waves. A zone of rock has been identified, with a possible volume equivalent to about one third to one half of the mass that moved on 22nd April 2002, that is at considerable risk of forming another major rock landslide into Safuna Alta. In such a case, the potential failure of the terminal moraine damming the lake is of considerable concern at Safuna. While it withstood the effects of the landslide in 2002, modelling shows that a subsequent event with a similar magnitude may well result in the terminal moraine being breached. In such a case, damage downstream is likely with a possibility of there being an impact at Huallanca. Safuna Glacier snout was covered by the landslide in April 2002 and forms no glacial hazard at present. The landslide debris is permeable and allows melt water to drain through it into the lake. Continued melting of the glacier is likely to destabilise the western rock slope that forms the boundary to the glacier and permit toppling failure to occur. However, it is highly unlikely that a further lake will develop in this region and any such landslides will have an impact only upon the immediate area beneath. Ice avalanche risks, although tangible from a west-facing glacier above Laguna Safuna Alta, are likely to be

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very small and decrease as the glacier ablates with time. Consequently, it is concluded that the only significant potential hazard is that represented by the high probability of a further major landslide into Safuna Alta. It is therefore recommended that remedial action is taken with a sense of urgency in order to repair the two existing tunnels through the terminal moraine to facilitate drainage from the lake in the event of the lake level rising in response to displacement by landslide material. Alternatively, it may prove more flexible, and would certainly be more beneficial to repair the 1978 tunnel and to construct an additional tunnel just above the current water line. Of greatest concern, however, is the stability of the terminal moraine, especially adjacent to the newer of the two tunnels, where the moraine has been weakened considerably by the April 2002 event. It is recommended that appropriate engineering works should be undertaken urgently to strengthen the moraine at this location. Such engineering works could involve the injection of grout or other cementitious materials into the dam to increase its competence. Alternatively, works could be carried out to drain the lake by a tunnel below the water line, either through the moraine or through the bedrock beside the lake. Both would involve tunnelling through unconsolidated deposits below the water table, a technique which is understood not to have been carried out previously in these circumstances. Any such engineering works would be logistically difficult in the circumstances and would need to be reviewed to assess their relative feasibility in this situation. Fully costed proposals would need to be developed for each viable solution to allow comparison. In the interim period it is recommended that the landslip is monitored by regular visits and if possible by instrumentation to record any movement, and especially any acceleration of movement. The size and levels of the lakes should also be recorded. Such monitoring should be carried out before and during any remedial works and should be linked to a response strategy that includes possible evacuation of the villages downstream and the Huallanca HEP.

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5 LAGUNA ARHUEYCOCHA 5.1 Introduction Laguna Arhueycocha is a proglacial lake impounded by a Neoglacial moraine complex on the west side of the Nevados Pacujirca massif in the northern Cordillera Blanca (Figures 5.1 and 5.2). The lake was identified in an ElectroPeru report as being potentially dangerous and requiring remediation by the construction of an engineered spillway (Marco

Zapata, pers. comm.). The recommendation was for the lake level to be lowered by 15 m, but due to financial constraints this was not possible and a spillway was constructed in 2000 to lower the lake level by 8 m (INRENA, 2001). The criteria upon which the recommendation was made are not known. The objectives of the present study are to (a) assess the nature of the glacier and lake system, (b) review the hazard assessment in the light of the current circumstances, and (c) make recommendations as to the future remediation requirements, if any.

Fig. 5.1: Location of Arhueycocha.

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Fig. 5.2: Overview of Arhueycocha. 5.2 Historical development of Arhueycocha Aerial photograph stereo pairs of the area are available from August 1950 and July 1963. In both sets of photographs the glacier flowing from Nevados Pucajirca reaches the end moraine and there is no lake. In the 1963 photograph the lower ca. 400 m of the glacier snout is pock-marked with irregular form ice cliffs similar to those commonly associated with transient supraglacial lakes (Figure 5.3). It is known that the formation and drainage of transient lakes can lead to the accelerated downwasting of debris-covered glaciers (Benn et al., 2001). From the evidence available it is not known when Laguna Arhueycocha first began to form. However, the glacier reaches the moraine ridge in an image from 1970, has three ponds in a photograph taken in 1989 and a mature proglacial lake in a photograph taken in 1994 (see Ames and Hastenrath, 1998). The lake is on the 2000 map (based on 1991 SPOT satellite data) as a 500 m long by 300 m wide body near the end moraine. Since 1991 the glacier snout has retreated ca. 500 m. A bathymetric survey of Arhueycocha was performed by INRENA in 2001 (Figure 5.4). The northern and southern flanks of the basin slope steeply into the lake, maintaining similar angles (35º) to the proximal sides of the lateral moraine ridges (Figure 5.5). The proximal end of the lake bottom forms a shelf sloping from the glacier at 12º for ~200 m, before dropping steeply (~67º) from 50 m to the deepest part of the lake at below 110 m. The distal slope rises uniformly at about 14º over the 460 m from the deepest point to the outlet in the south-eastern corner of the lake.

Fig. 5.3: Vertical aerial photograph of Arhuey Glacier before formation of Arhueycocha. Photograph acquired in July 1963. 5.3 Lake security measures During 1999 and 2000 a 122 m long open channel with a 12 m splay, was constructed through the southern lobe of the end-moraine complex (Figure 5.6). Beyond the concrete channel, a natural channel, possibly augmented during construction works, extends 88 m to a break in slope where the distal face of the moraine falls away at 32º, becoming shallower at 24º and then 12º. The low part of the end moraine complex is 120 m wide, with the cut spillway offset to its eastern side. 5.4 Field observations 5.4.1 Geomorphic setting The catchment of Laguna Arhueycocha is delimited by the glaciated peaks of Curuicashajana (5,510 m), Nevado Rinríjirca (5,810 m), Pucrapucraraju (5,780 m) and Pucajirca Oeste (6,039 m) to the east and Pucarashta (5,450 m) to the north (Figure 5.1). The lake is at an altitude of ~4,430 m and fills a glacially eroded bedrock basin. It is drained to the south by an unnamed stream that flows for 3 km through a broad hanging valley until the confluence with the Santa Cruz valley. Lagunas Jatuncocha and Ichiccocha are 6.5 km and 9 km down the Santa Cruz valley respectively.

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Fig. 5.4: Bathymetry of Arhueycocha. Unpublished INRENA plan, 2000..

Fig. 5.5: Inner flanks of the moraine dam at Arhueycocha: (a) the end-moraine and right (north) lateral moraine; and (b) the left (south) lateral. Note the larger than average instability in the left lateral (arrow).

a

b

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Fig. 5.6: (a) Construction of the channel close to the lake shoreline; and (b) the completed channel viewed from the downstream end, August 2002. 5.4.2 Moraine dam A latero-terminal moraine complex comprising three main ridges dams Laguna Arhueycocha. The right lateral moraine starts half way along the north shoreline of the lake where it begins as glacial sediments plastered against the glacially abraded bedrock wall. It develops into a single well-defined ridge separated from the valley side by an ablation valley. The steep inner flank of the right lateral moraine has small-scale instabilities and rises up to 50 m above the lake level. The left lateral is continuous from the end-moraine to the glacier snout, its crest reaching a height of c. 40 m above the lake level. The inner flanks of the lateral are inherently unstable as evidenced by failures at a variety of scales (Figure 5.5b). The end-moraine complex is characterised by two low-lying lobes at the locations of the former glacier snout (Figure 5.5a). Ice still exists within the end-moraine and is exposed at two locations close to the lake shoreline (Figure 5.5a). In addition, an irregular line of moisture 2-3 m above lake level is believed to reflect ice melting beneath the debris.

The southern end-moraine lobe is a low-lying area of moraine 200 m long by 150 m wide through which the engineered channel has been constructed (Figure 5.7). Much of this part of the moraine is less than 10 m above the lake. The surface of the moraine is relatively flat to the break of slope at the top of the distal flank of the moraine, which then has a slope of 32º. Four moraine ridges mark former positions of the glacier snout. The moraine surface comprises boulders in a silty sand matrix. There are no obvious signs of instability in the surface of the moraine and the material appears relatively weathered. A low relief combined with relative surface stability suggests that all ice has melted from this location.

Fig. 5.7: The southern lobe of the end-moraine complex at Arhueycocha. At the northwest corner of the lake is another low-lying area of moraine confined to the inner flank within a lobe of the end-moraine ridge crest. In comparison to the southern lobe, at this location there is ample evidence for instability of the moraine surface. Hummocks of debris near the shoreline have numerous small tension cracks on their surface. These are just above the ice exposed at the lake shoreline, and therefore it is reasonable to attribute the instability to the melting of buried ice. The upslope boundary of the hummocky moraine is sharply delineated by a gully (arrowed in Figure 5.8), above which are a series of active backscarps. On the aerial photographs from 1963 this lobe was filled with debris covered glacier ice. Active subsidence

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indicates that relict glacier ice is still melting beneath the hummocky moraine area and this is also reducing the support at the foot of the bounding slopes leading to their collapse.

Fig. 5.8: The southern lobe of the end-moraine complex at Arhueycocha. Arrows delineate a gully (see text). 5.4.3 Arhuey Glacier A profile of Arhuey Glacier, from its source on Pucajirca Oeste (6,039 m) to Arhueycocha (4,429 m), was constructed from the 1:100,000 scale Alpenvereinskarte map, modified using 1991 SPOT images. The position and altitude of Arhueycocha, which have changed substantially since the creation of the 1:100,000 map, were taken from the 2001 INRENA survey. Given the small scale of the map, calculated angles should be viewed as approximate values. From the summit of Pucajirca Oeste, ice descends at about 58º, decreasing to around 20º before becoming steeper, terminating in Arhueycocha at approximately 37º (Figure 5.9).

Fig. 5.9: Profile of Arhuey Glacier (numbers are slope angles in degrees).

Arhuey Glacier snout receives ice from three sources. Accumulation from the upper slopes in the southern part of the catchment (south of Nevado Rinríjirca) feeds into the south side of the tongue where it is pinched between the medial moraine and the bedrock valley side (Figure 5.10). Ice from the centre of the accumulation area (mainly from Pucrapucraraju) flows into the main part of the tongue on the north side of the medial moraine. Ice from the northwest side of the basin (e.g. from the slopes below Pucarashta) terminates on the rock slopes above the lake and avalanches onto the north side of Arhuey Glacier snout, as shown by an avalanche cone and increased debris cover.

Fig. 5.10: The composite tongue of Arhuey Glacier receives ice from three sources. Note the waves on the lake surface from a small ice avalanche event. Bedrock is visible at the foot of the glacier close to the water line in two places, indicating that the glacier is just beginning to retreat out of the lake onto the rock slope at its head (highlighted in Figure 5.11). The steep terminus is heavily crevassed across its width with blocks frequently calving from the snout. Several small events were witnessed per day involving volumes of ice of the order of 150 m3. Resulting displacement waves were of the order of

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only a few centimetres high and took between 1.5 and 2 minutes to reach the end-moraine (Figure 5.10). Some of the seracs on the glacier snout have estimated volumes up to 1,700 m3. This is particularly so on the north side of the snout where the avalanching appears to have increased glacier thickness.

Fig. 5.11: The heavily crevassed snout of Arhuey Glacier. Note the exposures of bedrock (ringed) indicating that the glacier is retreating onto the steep (~37º) bedrock slope at the head of the lake. 5.4.4 Constraining rock slopes The right side of the lake is bounded by a large face of apparently competent granitic rock (Figure 5.12). The major discontinuity set dips outwards towards the lake at 60º, perhaps slightly less at the base and decreasing westward to around 40º in the area north and northwest of the terminal moraine. Occasional persistent and many impersistent sub-vertical north-south striking joints terminate the outward dipping discontinuities. No evidence was seen for significant recent failures in this rock face. The southern valley side consists largely of morainic debris, cut across by two rock bands (Figure 13). Seepage of water was noted at intervals along this flank. A significant failure in the morainic material possibly associated with this seepage, was seen to originate at the base of the upper rock band and to give rise to a broad shallow gully cutting across and exposing the lower rock band (Figure 14). 5.5 Hazard assessment The key criteria affecting the hazard potential of Arhueycocha are listed in Table 5.1 according to the sub-environment; moraine, glacier, surrounding glaciers and rock slopes, etc.

Fig. 5.12: Right bank of Arhueycocha showing large face of granite rock. Note outward dipping discontinuities.

Fig. 5.13: Left bank of Arhueycocha showing morainic material with bands of rock. 5.5.1 Moraine complex Arhueycocha moraine ridge is up to 200 m wide and has gradients on the outer flank of the order of 30-32º. Modelling of moraine slope properties from other sites in the Cordillera Blanca and from global examples typically provides angles of internal friction (φ) of 36-40º. Given the width of the moraine and the low outer slope angle, it is difficult to see a major failure occurring on the outer flank under steady state conditions. The inner flanks along the lateral moraines are clearly unstable, although present instabilities are minor. It is expected that the buried ice in the end-moraine will continue to melt. Its outer limit in the western lobe of the moraine is fairly clearly associated with the well-developed gully, which extends for 100 m into the moraine complex. It is likely therefore that the lake shoreline will ingress into the moraine at this point by at most another 100 m. The moraine width close to the western lobe would then be reduced and the gradient of the inner flank would increase. Continued slumping of the inner flank would be

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expected. To obtain a better idea of the potential steady state stability of the moraine once all of the ice has melted it would be necessary to determine the thickness of the buried ice and obtain topographic profiles as inputs into slope models. The surface of the southern lobe is relatively stable and it is not thought that there is buried ice in this area.

Fig. 5.14: Left bank of Arhueycocha showing failure in morainic material exposing the underlying rock. Although the constructed channel has reduced the water level, it has also introduced a potential weakness into the moraine. The unprotected channel walls would be vulnerable to erosion from any displacement waves higher than ~1.5 m. There are also no downstream measures to protect from erosion should the discharge in the channel rise suddenly, such as through a displacement wave.

Table 5.1: Summary of the criteria affecting the hazard potential of Arhueycocha.

SETTING FACTOR COMMENTS

Dam geometry 200 m wide at southern lobe; 32º outer slope

Freeboard 6-10 m in southern lobe area (lowest point); up to 40 m elsewhere

Geology Bouldery, gravelly sand

Presence of buried ice

Yes - in western lobe of end-moraine None in southern lobe

Hydrogeology (e.g. springs)

Spring emergent ~50 m from right bank of stream, half way down outer flank of end-moraine

Moraine dam

Previous instability

Subsidence of western lobe on inner flank; minor instabilities on inner flanks of laterals; none on outer flank of moraine complex

Type of glacier margin (calving or hanging)

Calving/hanging transition

Relationship to lake

Terminates at water line

Surface gradient (<2° - lake growth; >25° - ice avalanches)

37º

Glacier structures

Well-developed transverse crevasses

Snout activity Regular (hourly) small calving events

Flow velocities unknown

Rate of snout advance/retreat

Retreating, rate unknown

Parent glacier

Glacier hydrology

Crevasses could provide pathways for water to reach the bed (lubrication)

Avalanches from local glaciers

Local glaciers surround upper part of lake

Rockfall/ landslides from valley sides

Discontinuities on north side favour plane failure. Evidence of failures in moranic material on south side.

Influence of adjacent glaciers/lakes

Avalanching risk - see above

Local environment

Existing remedial measures

Open channel cut, minimum protection in and downstream of channel

Regional environment

Tectonic activity Tectonically active area

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5.5.2 Potential trigger mechanisms The risk of an ice avalanche from Arhuey Glacier is considered high. From the literature, two morphological types of starting areas have been identified for ice avalanches: break-type (wedge failure) and ramp-type (slab failure) (Perla, 1980). In the break-type, the glacier forms a steep face, usually at a marked break of slope, and cracks into a series of seracs due to normal stresses. Avalanche volumes are usually <1x106 m3. In the ramp-type, the failure occurs due to gliding of a slab of glacier ice along the bedrock ice interface. Volumes of the latter type can be very large, >>1x106 m3, and in extreme examples comprise the entire hanging glacier. Empirical data from the European Alps show that ramp-type avalanching occurs for warm glaciers where slope angles are greater than 25º. The lower ~650 m section of Arhuey Glacier snout lies above the 25º threshold for potential slab failure. The snout also has a marked convex break of slope on the surface, which is likely to reflect a break of slope at the bed. Intense crevassing provides potential mechanisms for ice break-off. If this was to occur at the break of slope it could involve a volume of up to 4.6x106 m3 (assuming a glacier thickness of 30 m). Additional complexity is provided by the transition of the glacier snout into a hanging glacier margin as it retreats out of the lake. Previous behaviour of the glacier snout can no longer be taken as representative of future conditions. The risk of a large ice avalanche therefore needs to be considered seriously. Throughout the Cordillera Blanca avalanches from hanging glaciers have frequently triggered floods (e.g. Artesoncocha, Lake 513) and globally they are known to be by far the most common trigger for lake outburst floods (Richardson and Reynolds, 2000a). Predicting the timing of a potential avalanche will be difficult, even with thorough instrumentation and modelling of glacier flow velocities (cf. Margeth and Funk, 1999). Steep slopes bound both sides of the lake. On the north side the slope is apparently competent granitic rock with steeply outward dipping discontinuities. The potential exists for plane failure, probably on a relatively small or moderate scale (perhaps up to 104 m3). However, there is no evidence to suggest recent instability on a significant scale. Rock is also exposed in bands across the southern valley side. The same jointing pattern raises the potential for toppling failure in this slope, though on a much smaller scale. Once again, there is evidence for only a few small failures of this nature in the recent past. However, there is evidence of relatively large-scale instability in the moraine material in this flank. Hanging glaciers terminate on the rock slopes above the lake on both the valley sides, but more so on the

right (north) bank. The slope gradients of the glaciers on the north valley (~26º) side are close to the 25º threshold for avalanching of warm based glaciers, yet below the 45º empirically-derived threshold for cold based glaciers (Alean, 1984). Although no meltwater was seen from the glacier snouts, the glacier foreland is sub-glacially sculpted and therefore indicative of a warm based regime. A lack of obvious meltwater in August could be due to freezing of the surface during the dry winter months of May to September. It is thought that there is a potential for sliding of the upper glaciers, particularly during warmer and wetter periods in the austral summer when the many crevasses could provide a route for meltwater and precipitation water to reach and lubricate the glacier sole. Given the nature of the open channel, the moraine in the area of the southern lobe remains vulnerable to displacement waves produced by a large calving event or slide of Arhuey Glacier tongue, by rockfall from the valley side, or by avalanches from the hanging glaciers on the upper slopes above the lake. 5.6 Risk management Arhueycocha moraine appears to be stable in its steady state, yet potential outburst triggers include a slide of Arhuey Glacier tongue or, probably less likely, an ice avalanche from hanging glaciers to the north of the lake. The risk of avalanching from Arhuey Glacier will probably increase as the glacier retreats out of the lake into a higher hanging position. The likelihood of an outburst flood from Arhueycocha is therefore high under current and predicted short-term conditions. Vulnerable targets include tourists, grazing land and areas of ecological importance within the National Park. A strategy is required to minimise the risk represented to these vulnerable targets, employing a combination of monitoring, lake security works and vulnerability reduction measures subject to cost-benefit analyses that need to be undertaken by the involved agencies within Peru (e.g. INRENA, INDECI and National Parks). Possible solutions are discussed below. 5.6.1 Monitoring At the very least, the snout of Arhuey Glacier should be visually inspected to assess change in the nature of the crevasses. It may be possible to identify a potential break-off point if it develops through significant widening of a transverse crevasse. Such observations need to be undertaken by repeat photography from field visits or by using high-resolution satellite images (of at least 1 m spatial resolution), the latter being expensive. ‘Moraine Camp’ below Nevado Alpamayo would be a good

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location to obtain photographs with a standard 35 mm camera and telephoto lens. More detailed monitoring is technologically possible by surveying target prisms mounted on the glacier, but is logistically demanding and expensive. Application of this technique in the European Alps has shown that prior to break off the surface flow velocity increases in a hyperbolic form (Flotron, 1977). An empirical formula relates the velocity of the unstable ice mass to time, allowing calculation of the time of break off: a v = v0 +

(t� - t) (1)

Where v is flow velocity, t is time, and v0 and a are constants that can be calculated. Results from this approach have been impressive, as the timing of avalanches have been predicted to the nearest day (Margeth and Funk, 1999). Because of the difficulties of placing sensors and the high associated costs, instrumented monitoring of hanging glaciers has only been done in situations of high vulnerability, such as where whole villages were threatened. The method is also employed where the infrastructure exists to have real-time monitoring combined with a safety plan for avalanche warning and evacuation. This requires the subsequent behaviour of the hazard to be predictable, as is possible with avalanche runout routes (Alean, 1984). In the case of Arhueycocha, it is probably not appropriate to consider instrumented monitoring because of the high cost, lack of monitoring infrastructure and warning system, unpredictability of the effect of an avalanche on the moraine dam, and the uncertainties of potential runout route should the dam fail. The inner flank of the moraine complex should be regularly inspected, particularly the western lobe where there are signs of melting buried ice. In order to better define the stability of the moraine at this point, the thickness and extent of the buried ice could be investigated using geophysical methods. Ground Penetrating Radar and electrical resistivity used in conjunction have produced good results from comparable situations in the Himalayas (Pant and Reynolds, 2000; Rana et al., 1999; Richardson and Reynolds, 2000b). Moraine stability calculations based on the predicted topography after removal of the ice could then be undertaken. At the moment, the southern lobe has the lowest freeboard of any part of the moraine and is the most likely to be overtopped if there is a large displacement wave. If geophysical methods were employed at the site, it would be worth undertaking a survey of the southern lobe to confirm that no ice is present there.

5.6.2 Lake security measures –recommendations Undoubtedly, the most effective means of reducing risk is to remove the hazard. Success has been achieved at 33 lakes in the Cordillera Blanca by employing engineered security works. Although it is not always possible to state whether any of the lakes would have failed without the security works, none have failed since their works were completed. The open channel in the Arhueycocha end-moraine is vulnerable to erosion from displacement waves. As a minimum recommendation, a reconstructed dam is needed to protect the spillway and to provide additional freeboard. The amount of drawdown required reflects the need for adequate freeboard to protect against displacement waves of the largest magnitude foreseeable. This is extremely difficult to predict and events from elsewhere in the Cordillera Blanca indicate that displacement waves in excess of 100 m high are possible. However, it is necessary to make a judgement on some practically achievable amount of downdraw that would be expected to provide protection against most events. Such a judgement may indicate that figures of 15 m to 20 m of freeboard would be appropriate, i.e. a further 7 m to 12 m of downdraw. 5.7 Conclusions Laguna Arhueycocha has developed between the retreating tongue of Arhuey Glacier and its Neoglacial moraine complex. Arhuey Glacier has retreated onto the steep rock wall at the head of the lake and now the lower ~650 m of its terminus is steeper than the 25º threshold for potential slab avalanche failure. If an avalanche occurs, with a break off point at the marked change of slope, it could involve up to 4.6x106 m3 of ice and trigger a significant displacement wave. An open channel constructed through the end-moraine has reduced the level of the lake by 8 m, reducing the amount of water available to form a flood, although the channel itself is vulnerable to erosion from a displacement wave. It is recommended that the moraine dam be capped with a constructed embankment to provide protection to the open channel and to increase the freeboard. In addition, if the lake level could be reduced further it would reduce the risk from overtopping following an ice avalanche into the lake. At this stage, there is insufficient information available to determine the probability that a potential displacement wave will reach a certain height. On the basis of successful empirical examples of lake security works in the Cordillera Blanca, it is recommended that the lake should be drawn down the maximum practical amount and at least a further 7 m to 12 m.

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6 LAGUNA LLACA 6.1 Introduction Laguna Llaca (9º26’00”S, 77º26’30”W) is a moraine-dammed lake located at the head of Quebrada Llaca, 13 km north-east of the centre of Huaraz (Figure 6.1). It developed at the snout of an unnamed debris-covered valley glacier fed by clean ice, snow and debris from the south-western slopes of Nevado Panrapalca (6,162 m) (Figure 6.2). Based on measurements from an ASTER satellite image acquired in 2001, it is c. 295 m long, c. 190 m wide and has an area of 43,000 m2. A single day was spent at the site to investigate the affect of remediation works completed in 1977 upon the lake and to consider the current and potential hazard.

Fig. 6.1: Location of Laguna Llaca. 6.2 Lake security measures The aluvión from Laguna Palcacocha in 1941, which travelled down the next valley south of Quebrada Llaca and killed at least 4,000 people in Huaraz, triggered an investigation of other potentially dangerous lakes in the Cordillera Blanca. The search began close to Huaraz and Laguna Llaca was soon recognised as hazardous. From the 1948 aerial photograph it can be seen that the lake was very well-developed; the freeboard of the end-moraine was minimal, the dam was very narrow, and the glacier entered the lake as a near-vertical, calving ice cliff (Figure 6.3). Initial security works helped to draw the level of lake down in the early 1950s (pers. comm. Marco Zapata, INRENA) although the detail of the work is not known. It is thought that the effect of the security measures can be seen on the 1962

aerial photograph; freeboard was increased and the lake area has decreased (Figure 6.3). Fresh alluvial deposits immediately downstream of the lake spillway presumably were deposited during peak discharges as water was drained from the lake. Between 1948 and 1962 the position of the glacier snout appeared to advance slightly, but it is not known whether this

Fig. 6.2: ASTER false colour composite satellite image if Llaca glacier and lake.

Fig. 6.3: Aerial photographs from (a) August 1948 and (b) June 1963. Note the breach deposits in the latter image.

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reflects ice flow or emergence of the previously submerged ice as the water level was reduced. The original security measures were damaged in the 1970 earthquake, requiring reconstruction that was completed in 1977. An open cut and rock-fill artificial dam were used to drawn the water level down by a further 10 m (Figure 6.4). Gabions were used to stabilise the moraine slopes on the right bank of the cut, but no stabilisation work was necessary on the left bank (Figure 6.5). Prior to the repair work, the lake had a recorded area of 63,312 m2, volume of 749,000 m3 and maximum depth of 29 m, whilst afterwards these figures were reduced to 36,947 m2, 299,400 m3 and 19 m respectively (INRENA, 2002).

6.3 Present condition of Laguna Llaca and glacier

6.3.1 Glaciological setting Laguna Llaca’s glacier is fed by ice from the headwall of a cirque defined by the peaks of Nevado Panrapalca (6,162 m) and Nevado Ocshapalca (5,881 m). The ice flows through an icefall into the valley glacier tongue, which is debris covered over its lower 2 km. Other mountain glaciers exist high on both sides of the valley (Figure 6.6). Neoglacial retreat of these glaciers is shown by complexes of multiple moraines, particularly on western valley side, and relatively fresh glacially polished bedrock, especially on the eastern valley side. The main valley glacier has retreated c. 300 m from end-moraine allowing the development of Laguna Llaca. Its surface is generally between 30-40 m below the crest of its lateral moraine ridges, indicating that a lot of mass has been lost through downwasting.

Fig 6.4: Artificial dam at Laguna Llaca (from INRENA).

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Fig. 6.5: Artificial dam at Laguna Llaca.

6.3.2 Llaca Glacier Llaca glacier terminates at the upstream margin of Laguna Llaca as a debris-covered transverse ridge that is being colonised by shrub vegetation. The lower 430 m (100,000 m2) of the glacier snout is undergoing thermokarst degradation with many supraglacial ponds, some of which are interconnected (Figures 6.7 and 6.8). An ice cliff extending across the whole width of the glacier (230 m) marks the upstream limit of the thermokarst (Figures 6.6 and 6.9). The ice cliff is c. 725 m from the downstream end of the lake, up to c. 10 m high on its left bank, is near vertical to overhanging, and loses mass through calving. Upglacier of the ice cliff the glacier surface is very different in form to the thermokarst area. Although well below its lateral moraine crests, and thus indicating extensive downwasting, the glacier is not degrading in the same manner of the lower tongue. It is far more uniform with frequently exposed ice cliffs, and has fewer supraglacial ponds (Figure 6.10). Exposed englacial channels (Figure 6.11) provide potential drainage routes for the supraglacial ponds. It is

Fig. 6.6: Geomorphology of Llaca Glacier.

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suggested that the perched ponds drain periodically as pond expansion causes the basin margins to intercept such conduits or structural weaknesses, as has been documented on other debris-covered glaciers (cf. Benn et al., 2001).

Fig. 6.7: Laguna Llaca from the moraine dam. The position of the glacier snout in 2002 appears to be comparable to that shown on the 1962 aerial photograph, although the form of the snout is markedly different. In 1962, there was no evidence of the extensive glacier karst now characterising the lower reaches. The irregular hummocks, extensive ponding and vegetation growth are indicators that this area is stagnating. It is now unlikely that there is a dynamic connection between the thermokarst area and the rest of the glacier. Given the distinctive change in glacier form upstream of the ice cliff, it is thought that the ice cliff represents a newly developing snout position. 6.3.3 Moraines Laguna Llaca and its glacier are contained within a latero-terminal moraine with a single ridge crest. The height of this crest increases form c. 15 m above the lake at the end-moraine to c. 40 m above the terminus of the glacier. The inner flanks of the moraines show varying amounts of planar and

rotational instability. Mostly, in the moraines adjacent to the lake and thermokarst area, the failures are superficial and associated with the gradual downwasting of the glacier. Further upstream, in the upper regions of the debris-covered area, there is a large slip on the left bank where an 800 m length of the moraine has failed back to bedrock. The backscarp for this failure could bee seen developing in the 1948 aerial photograph (Figure 6.3a) and by 1962 the moraine had failed (Figure 6.3b).

Fig. 6.8: Thermokarst disintegration of the snout of Llaca Glacier.

Fig. 6.9: Calving front of Llaca Glacier. 6.4 Discussion 6.4.1 The GLOF Source Parameter system In order to identify the levels of past and current hazard represented by Laguna Llaca, the contributory factors have been considered in terms of an empirical scoring system (Table 6.1) (RGSL, 1998). The factors have been determined from global examples, and for each one a score of 0, 2, 10 or 50 is estimated depending on whether the scale of that factor is none, low, moderate, or large. The same system is used for each parameter and the scores are added together to give a single value which is the

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GLOF Source Parameter. This value is compared with an empirical scale indicating potential hazard (Table 6.2). Where a GLOF Source Parameter score exceeds 100, then an outburst is considered to be likely at any time. The higher the score the more imminent or more serious is the perceived hazard.

Fig. 6.10: The calving ice front of Llaca Glacier separating stagnant ice (left) from the dynamic part of the glacier (right).

Fig. 6.11: Exposed englacial conduit. 6.4.2 Affect of remediation on hazard status The GLOF Source Parameter scores have been used as an aid to illustrate the changing hazard posed by Laguna Llaca over time. Changes in the level of hazard are principally affected by the development of physical processes and by the construction of remediation works. Observations of the 1948 aerial photograph provide a GLOF Source Parameter score of 116, which equates to a moderate level of hazard. The key factors in determining the hazard at this time were the minimal freeboard and the large calving risk from the steep ice front. The score suggests that an outburst could have occurred at any time. The fact that the lake was considered to be dangerous and a

decision was made to remediate it helps to validate the accuracy of the scoring system. By 1962, the lake level was lower compared to that in the 1948 aerial photograph. There was a breach through the moraine and fresh breach fan deposits extended downstream for ~1 km. It is not clear from the photographs whether the breach is natural or man made, although it is thought that engineering work was undertaken in the 1950s (Marco Zapata, INRENA, pers. comm.). The ice cliff was also considerably less steep and thereby offered less of a calving risk. Both of these previously maximum scoring parameters therefore have reduced scores, which reduces the overall GLOF Source Parameter score for Laguna Llaca in 1962 to 36, corresponding to minimal hazard. The other key effect of lowering the water level was to reduce the amount of water in the lake able to be incorporated in an outburst. Again, this helped to further reduce the overall GLOF Source Parameter score. Table 6.1: GLOF Source Parameter scores for Laguna Llaca between 1948 and 2002. Information for 1948 and 1962 was taken from aerial photographs; 2002 information obtained from field visit and ASTER satellite imagery.

1948 1962 2002

Criteria affecting hazard Score Score Score

1 Volume of lake Mod. 10 Low 2 Low 2

2Calving risk from ice cliff

Large 50 Mod. 10 None 0

3

Avalanche risk from hanging glaciers

Low 2 Low 2 Low 2

4Lake level relative to freeboard

Full 50 Mod. 10 Mod. 10

5

Seepage evident through

dam

None 0 None 0 None 0

6

Ice-cored moraine dam +/-

thermokarst features

None 0 None 0 None 0

7Compound

risk present

Slight 2 Slight 2 None 0

8Supra- / englacial drainage

Low 2 Mod. 10 Mod. 10

GLOF

Source Parameter

116 36 24

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Table 6.2: Hazard rating on the basis of GLOF Source Parameter scores.

0 50 100 125 150+ Zero Minimal Moderate High Very

high >>>> An outburst can occur at

any time>>>> 6.4.3 Current hazard status The situation as of 2002 is quite similar to that in 1962 as far as the scoring system is concerned. The calving risk is now zero because the active calving front has migrated up glacier and the thermokarst area offers protection against displacement waves and the compound risk is therefore also absent. As a consequence the overall score has fallen slightly to 24, i.e. still representing minimal hazard. On account of the engineering works, the freeboard of the moraine is at least 10 m and the lowest point of the moraine is protected against erosion by the artificial dam. Although the inner flanks of the terminal and lateral moraines show varying amounts of planar and rotational instability, all past failures have been superficial and do not appear to have threatened the integrity of the moraine complex. There is no reason to suggest that this situation will change. In the same manner, protection is provided against displacement waves from other trigger mechanisms such as rock and/or ice avalanches. Ice avalanches are unlikely at present; the glacier is of the valley type, not hanging above the lake, and is unlikely to produce ice avalanches until the snout retreats by 1 km to the steeper debris-free headwalls where gradients closer to a critical avalanche threshold of ≥25° could be reached. Significant calving events are also unlikely given a relatively low ice cliff and the full protection offered by the debris-covered island that would help dissipate wave energy. 6.4.4 Future development of hazards The current GLOF Source Parameter score does not take into account the future hazard as the lake develops. Given a scenario of continued melting, there is a probability that the degree of hazard posed by Laguna Llaca will increase. The main predicted change in the system is the continued degradation of the glacier snout, leading to the growth of the lake, both in area and depth. It is possible that lake expansion could take place over a period of just a few years. It appears that the new glacier front is developing behind the thermokarst area. Expansion of the lake to this point would increase the length of the lake from 290 m to 725 m and its area from

43,000 m2 to 143,000 m2. As the thermokarst area becomes submerged it will lose mass by sub-aqueous melting rather than calving. Rates of melting are difficult to predict, although estimates of 2.9 ma-1 have been suggested for the base of Himalayan lakes (Yamada, 1998). If the glacier karst area subsides at an average of 2.9 ma-1 for the next 10 years and the current lake area retains an average depth of 8 m, then the potential average depth and volume of the lake could increase to c. 2.5 x 106 m3. If the ice cliff represents a newly forming terminus, it is likely to become higher as the glacier snout retreats (subject to a greater rate of calving than downwasting). In this scenario, greater calving events could occur in the future. Nevertheless, if the 10-m high freeboard is maintained it is unlikely that the artificial dam will be overtopped. Displacement waves from ice calving events have rarely been recorded in excess of 2 m high in comparable environments. Rock avalanches from valley sides have the capability to generate much larger displacement waves. There are steep rock faces on the right bank and currently upglacier of Laguna Llaca that could represent a risk if the lake expands, although information on structural discontinuities would be needed in order to assess their susceptibility to failure. It is not known how the current environment would be affected by a major earthquake but it should be remembered that the engineering works were tested by the 1970 earthquake and, although repairs were needed, the dam was not breached. A predicted GLOF Source Parameter calculation is given in Table 6.3 based on the above predictions and assumptions. By increasing the volume of the lake, including the risk of large calving events and the likelihood of additional triggers such as rock avalanches, the level of hazard rises close to a point predicting failure at any time. Table 6.3: Predicted GLOF Source Parameter scores for Laguna Llaca under a scenario of continued melting and lake expansion.

Predicted Criteria affecting hazard Score 1 Volume of lake Moderate 10 2 Calving risk from ice cliff Large 50

3 *Avalanche risk from hanging glaciers &/or rock cliffs Moderate 10

4 Lake level relative to freeboard Moderate 10 5 Seepage evident through dam None 0

6 Ice-cored moraine dam +/- thermokarst features None 0

7 Compound risk present Moderate 10 8 Supra- / englacial drainage Moderate 10 GLOF Source Parameter 100

*Includes potential rock avalanches

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6.5 Recommendations The indication that the hazard posed by Laguna Llaca could increase into the future highlights the need for monitoring, particularly of the following aspects:

�� the degradation rate of the thermokarst area on the glacier snout;

�� the developing glacier ice cliff upglacier of the thermokarst area; and,

�� the nature of the valley sides upglacier of the glacier terminus, with respect to possible rock avalanche triggers.

6.6 Conclusions A single day was spent at Laguna Llaca to investigate the affect of remediation works completed in 1977 and to consider the current and potential hazard. Laguna Llaca has developed on the debris-covered snout of a glacier flowing from the south-western slopes of Nevado Panrapalca. It is dammed by a well defined latero-terminal moraine rampart with a narrow sharp crest. The inner flanks of the moraine are unstable but there are no major failures adjacent to the lake. The lower reaches of the glacier snout show signs of mature thermokarst decay, upstream of which a calving ice cliff is developing that is presumed to be a newly forming terminus. Original engineering work to remediate Laguna Llaca was undertaken in the 1950s, but the constructed channel and dam were damaged in the earthquake of 1970 and subsequently needed repairing. The current channel and stone/concrete dam were completed in 1977 and provide 10 m of freeboard. A semi-quantitative assessment of the criteria that lead to glacial lake outbursts has demonstrated the effectiveness of the engineering works in reducing the hazard. Under a scenario of continued warming and lake expansion, the same assessment predicts an increase in hazard to a point close to the threshold for an outburst. For this reason, it is recommended that the decaying glacier snout and the newly developing ice cliff are monitored and that the valley sides are surveyed for potential rock avalanche triggers.

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7. NEVADO HUASCARÁN 7.1 Introduction Most of the sites examined in this project, on which protocols for hazard assessment are being based, are glacial lakes. In contrast, Nevado Huascarán, the highest mountain in the Cordillera Blanca (6,768 m), has a history of producing catastrophic landslides, sturzstroms, and ice avalanches and is probably the site that engenders greatest concern locally. The interplay between the physical processes of sturzstroms and the local response to the threat, perceived or otherwise, provides an opportunity to consider appropriate management responses to supplement the protocols being developed primarily for glacial lakes. During the field visit, staff from RGSL and INRENA undertook an aerial circuit of the mountain in a fixed wing aircraft, and they also visited two viewpoints to obtain photographs of the western aspect of the massif. Meanwhile, a sociological survey of the local population and a review of existing management practices by the local authorities were carried out by Lima-based sub-consultants Asociación SER (see Chapter 8). The purpose of the exercise was to obtain information that can be used by INRENA to help plan a management strategy. The socio-economic survey provides insight into the perception and communication of risk issues previously lacking in the area. Photographs acquired have been provided to INRENA to augment similar images acquired over the years and kept in their archive. The purpose of this document is to make recommendations as to how an appropriate management strategy could be developed and implemented given adequate resources. 7.2 Physical and geological setting Nevado Huascarán lies towards the northern end of the Cordillera Blanca (9º06’S, 77º36’) and has two main peaks; Huascarán Norte (6,664 m) and the higher Huascarán Sur (6,768 m) (Figure 1.1). The massif is bound by the deeply incised glaciated valleys of Quebradas Ulta to the south and Quebrada Llanganuco to the north. The Cordillera Blanca is dissected by many such roughly east-west trending glacial valleys. These frequently contain moraine- and landslide-dammed lakes, such as the Lagunas Llanganuco in Quebrada Llanganuco. Drainage from the west face of Huascarán Norte flows via Quebradas Huarayoc and Armapampa into the Río Ranrahirca, which drains to the southwest across the debris fan affected by sturzstroms in 1962 and 1970, and then northwards into the Río Santa, which is the main river draining the Santa basin. North of the Río Ranrahirca is the site of old Yungay, which was

buried in a sturzstrom in 1970, and has been declared a national cemetery. The new town of Yungay has developed 1.5 km further north in the lee of a 600 m high hill. The elevation difference between Huascarán Norte and Yungay is 4,100 m over a horizontal distance of just 14 km (average gradient = 16º). Upper slopes on Nevado Huascarán are extremely steep (70º-90º) and, in common with many other areas of the Cordillera Blanca, are locally unstable. Cluff (1971) reported that small snow and ice avalanches occurred almost daily along some parts of the range and that major rock and ice avalanches were reported yearly. Huascarán appears to be particularly unstable, producing three major avalanches of mixed ice and rock; those in 1962 and 1970, and a Pre-Columbian event, and climbers report regular snow and ice avalanches. The geology of the Cordillera Blanca comprises intrusive granodiorites, with steeply dipping sedimentary rocks outcropping on the valley sides in some places. The range’s abrupt and steep western margin is associated with uplift along a normal fault. To the west, the lower Cordillera Negra is composed largely of volcanic deposits including basalt, andesite and rhyolite flows and ash deposits, and does not support a permanent snow cover. Evidence from road and stream cuttings throughout the area indicates that debris flow deposits infill much of the Río Santa basin and that some of the past failures were larger than the 1970 event. This evidence ‘strongly suggests that the area...will continue to be overridden…’ (Cluff, 1971, 511). 7.3 Historical aluvión events Huascarán has repeatedly been a source of large and rapid mass movement events. The 1970 catastrophic mixed rock/ice avalanche or sturzstrom, in particular, is well documented with several harrowing eyewitness accounts (e.g. Cluff, 1971; Lomnitz, 1971; Clapperton and Hamilton, 1971; Browning, 1973). On the 31st of May 1970 an earthquake with two tremors > magnitude 7 caused widespread damage in northern Peru (Lomnitz, 1971). Thousands of landslides were triggered, with by far the most significant occurring on the south-west face of Huascarán Norte. An estimated mass of rock and ice of >2x106 m3 fell almost 1,000 m (Browning, 1973). Following this freefall, the debris flowed at speeds up to an estimated 250-400 kph. During this phase, the avalanche overtopped a 150 m ridge, as an 80 m wave, that had protected the town of Yungay from a smaller event in 1962. Yungay and its satellite settlements were destroyed. The reported number of fatalities due to the sturtzstrom is often given as 23,000 with 18,000 of these from Yungay,

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Fig. 7.1: Extent of the 1962 and 1970 catastrophic rock avalanches from Huascaran (redrawn from Plafker and Ericksen, 1978). although Clapperton and Hamilton (1971) highlight cases of overestimation in comparison with population data from the 1961 census. A few people from Yungay survived by running up a small hill on which the town cemetery is situated. The landslide continued as a mudflow down the Rio Santa for a further 50 km, where it destroyed a 50 m high concrete gravity dam associated with the Huallanca hydropower plant (Cluff, 1971). The plant had enough warning to close the safety gates at the intake tunnels and as a result the turbines were spared major damage. An earthquake triggered the 1970 aluvión. However, a smaller catastrophic event in 1962, which destroyed Ranrahirca and eight other villages, killing 3,500 people, had no seismic trigger. Instead an unusual thaw of the west face of Huascarán Norte leading to the break-off of an ice cornice has been invoked as the trigger (Clapperton and Hamilton, 1971). However, Clapperton and Hamilton (1971) also ascribe the 1970 event to an ice cornice avalanche, when it is widely recognised as primarily a rock failure. The runout of large avalanches (>1.5x106 m3) exceeds that accounted for through frictional sliding, and field evidence and eyewitness reports clearly suggest that such events flow (cf. Selby, 1993). To account for this, a number of hypotheses have been proposed. At the time of the event, trapped cushions of air or fluidisation through leaking air were popular

ideas. Examination of these hypotheses is beyond the scope of this report, although it is worth noting that while high water content and air launching of the debris may have added to the fluidity of the event, hypotheses invoking cohesionless grain flow and explosive energy from the shattering of clasts have superseded earlier ideas. 7.4 Field observations of Nevado Huascarán Huascarán Norte has four main ridges extending roughly to the north, south, east and west from the summit, whilst Huascarán Sur is pyramidal with north-east, south-east and west ridges. Mountain-type glaciers dominate the south-east, south-west and north-west faces of both peaks, whilst the valley-type glaciers Glaciar Kinzl and Glaciar Schneider drain the north-eastern side of the massif. Glaciers and rock faces on the south-west and north-west faces of the massif are those that have historically led to the loss of life. The north-west face of Huascarán Norte was best viewed from the mountain flight (Figure 7.2). The north ridge divides into two, separating minor accumulations of ice on a steep headwall (in shadow, Figure 7.2) from a well-defined mountain glacier to the north. This glacier is heavily crevassed and has an approximate surface gradient of 26° (from the topographic map), which, as the glaciers are thin, is believed to be a fair reflection of the basal slope. The

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headwall behind the glacier rises steeply from an altitude of 5,600 m to 6,400 m with an average gradient of 63°. It is thought that this glacier produced an avalanche that killed 14 tourists in the Llanganuco valley during the 1970 earthquake.

Fig. 7.2: The north ridge and north-west face of Huascarán Norte, showing well crevassed mountain-type glacier.

The south-west face of the Nevado Huascarán massif has been viewed from the mountain flight and from vantage points in the Río Santa valley. Ice-clad upper slopes reach angles of at least 48°, from where the ice flows into a series of discrete glacier snouts with surface angles between 17° and 26° (Figure 7.3). The upper south-west face of Huascarán Norte is a mixed ice and rock face (Figure 7.4). Above the

Fig. 7.3: Oblique view of the south-west face of the Nevado Huascarán massif, Huascarán Sur is closest to the camera; Huascarán Norte is the next peak to the left.

Fig. 7.4: The south-west face of Huascarán Norte; source of the devastating sturzstroms of 1962 and 1970.

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crevassed lower parts of the glacier the face steepens with increasing exposures of rock. Above it is a mixed section with alternating south-westward dipping bands rock and ice below a more substantial rock band. This main band of rock occupies about a quarter of the height of the face and it is from here and the ice above it that the devastating sturzstroms of 1962 and 1970 are said to have begun. There is a dominant discontinuity pattern that dips in a south-westerly direction, out of the face and down to the right as the mountain is viewed face on. Above the main rock band is a thick band of ice forming the edge of the glacier occupying the less steep summit slopes. To the south of centre of the face, ice avalanche debris is found in the upper reaches whilst the lower glacier is covered with debris supplied from the rock face. It seems likely that these indicate ongoing small scale instability. The less steep lower part of the glaciers on Huascarán Norte and Sur are relatively thin (≤30 m) compared with the upper ice accumulations. Both the upper and lower reaches of the glaciers are heavily crevassed. On the south peak there is a distinct ice cliff about 50 m high that marks the rear point of a full depth ice slide (arrowed in Figure 7.5). Other extensive crevasses in the steeper upper sections mark potential release points for large ice slides. A pair of parallel apparent crevasses on the summit dome of Huascarán Norte is of particular interest. According to INRENA staff these have only developed recently. A concern is that they are

responding to an increased rate of movement of the ice cap that could be a precursor to a large avalanche. The lower reaches of the glaciers on Nevado Huascarán are close to the 25° threshold angle for sliding of warm-based ice (Alean, 1985). The basal condition of the glaciers is not known, although ice core records from Huascarán and Quelccaya Ice Cap in southern Peru have shown that these glaciers are close to the melting point, with the 0°C isotherm at an altitude of 5,700 m for the latter (Thompson et al., 2000). For the purpose of determining avalanche susceptibility, it must therefore be assumed that the glaciers are not frozen to their bed and are free to slide. Evidence of sliding on Huascarán Sur further supports this assumption. The intense crevassing observed on most of the glaciers is likely to increase the tendency to avalanche both by aiding mechanical failure and by allowing water to percolate and provide lubrication to the bed. Given that the slope gradients increase towards the upper part of the massif, it is also likely that glacier slides and/or avalanche activity will intensify as the glaciers recede. It is worth noting that whilst glacier bed gradients can provide an indication of susceptibility to avalanching, the empirical relationship established in the European Alps has not been tested for glaciers in the tropics. It is best viewed as a guide only.

Fig. 7.5: The south-west face of Huascarán Sur. Note the ice cliff (arrowed) in the upper part of the glacier referred to in the text.

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7.5 Managing the hazards and risks from Nevado Huascarán It is clear that Nevado Huascarán has repeatedly produced devastating sturzstroms or aluviones, and there is no reason to think that this will change. Despite regulations forbidding the resettlement of the area affected by the 1970 aluvión, by the 1980 these areas were being cultivated and resettled. It is likely that any subsequent aluviones of comparable size will again impact upon many people and their activities. To help manage such risks, a better understanding of the hazard and particularly people’s vulnerability is needed. Steps that could be taken by the authorities are considered below. 7.5.1 Hazard assessment and monitoring techniques 7.5.1.1 Hazard assessment It may be possible to determine the degree of hazard offered by Huascarán and to map hazard zones using the previous events for guidance. For ice avalanches, glaciological analysis may recognise dominant structures that could represent potential avalanche starting zones, allowing break-off volumes to be calculated for input into avalanche models. High resolution and geospatially correct data would best provide this information, such as newly acquired aerial photographs or optical images from satellite platforms such as IKONOS and Quickbird that offer pixel resolutions of 1 m or better. For potential rock failures, if material types and discontinuity patterns in the rock face can be better determined, then mathematical models for slope stability calculations may be applied. Various software packages are available that could be used to provide an indication of the probability of failure for a given size of event. Findings from geotechnical and glaciological studies could be used to calibrate avalanche and debris flow dynamic models. Various debris flow models exist, although a simple terrain-based model applied in a Geographical Information System (GIS) has been proven for sites in the European Alps (Huggel et al., 2003) and has already been applied to hazard mapping studies in Peru (Figure 7.6). Ice avalanche dynamics are determined using carefully chosen parameters such as ice volume, geometry of the falling ice and friction coefficients. No universal ice avalanche model exists to calculate runout distances (Margeth and Funk, 1999). However, as the ice bursts apart, various dry flowing snow avalanche models have been used successfully.

Fig. 7.6: Example of a GIS-based hazard probability model for debris flows in southern Peru (RGSL, 2003). Existing vertical aerial photographs from 1970 held by INRENA could be used to provide the topographic control needed for the debris flow models. A trial of digital photogrammetry techniques using similar photographs from 1962/63 has demonstrated that high quality Digital Elevation Models can be produced (Figure 7.7). Using this information combined with the modelling approaches mentioned above, the probabilities of inundation by an aluvión could be calculated and mapped. Once this information is available, the distribution of population and other targets could be recorded, and evaluated, in order to define the levels of risk for the areas down valley of Huascarán. 7.5.1.2 Monitoring Monitoring the rock slopes and glaciers of Huascarán could serve two main purposes. It would lead to a better understanding of the processes operating over time; information that could be used to improve the accuracy of the original hazard assessment. It could also form the basis of an early warning system by allowing the identification of anomalous rates of change that could be precursors to an avalanche. Successful cases of monitoring to help reduce risks have been reported in the literature. A slowly opening crevasse was observed towards the rear of the Whymper Glacier, Grandes Jorasses, Italian Alps. As this suggested that the whole glacier might fail, eleven pillars with target prisms were erected and surveyed with theodolites and distometers (Margeth and Funk, 1999). The velocity increased from 7 mmd-1 to 14 mmd-1 leading to a prediction that 10,000 to 25,000 m3 of ice would fall between the 20th and 22nd of January 1997. As there were good grounds to believe that the ice avalanche would trigger secondary snow avalanches, which would reach a nearby village, the settlement was evacuated. Fortunately the snow

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Fig. 7.7: A mosaic of aerial photographs from 1962/63 draped over a Digital Elevation Model produced from the same images by digital photogrammetry. The path of the 1962 aluvión is clear. The DEM was produced in a separate research project in collaboration with the Department of Geography, University of Zurich. pack stabilized between the evacuation and the ice avalanche and remained in place. In the case of Huascarán, it is unlikely that the face can be monitored directly by instrumentation of the face due to its inaccessibility. It may be possible though to monitor the face by stereoscopic terrestrial photogrammetry carried out from established vantage points in the Cordillera Negra or from the hillside above Arhuey. Alternatively, a technique such as LIDAR scanning from a fixed wing aircraft could be used to provide detailed (10-20 cm resolution) terrain information suitable for identifying changes in distinct features (e.g. crevasses) and glacier velocities (Kennet and Eiken, 1997; Abdalati and Krabill, 1999; Favey et al., 1999). It is not

known whether this technology is available in Peru at present, although given the previous scale of aluviones and losses, at this stage all options for data collection should be considered. It should be noted that the 1970 event occurred as a result of a major earthquake. Instability triggered by such an external event is unlikely to be predicted by monitoring the face. However, hazard maps based on models calibrated by the 1970 event could take earthquake triggers into account.

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7.5.2 Risk reduction 7.5.2.1 Reducing hazard It is difficult to see that any remedial measures could be implemented on such a large and remote face that would result in an adequate increase in stability. Extrinsic causes of a rock avalanche, such as the reduction of frictional support within the discontinuities in the face during an earthquake, cannot be stopped. It may be possible to deliberately trigger an event, using explosives, and thus to bring down an unstable mass. However, there is no guarantee, even if the towns were evacuated, that the damage could be limited. Dependent upon the size of such a mass, major damage is likely to occur in the villages below and possibly in the more distant towns, the road may be destroyed and the river blocked with consequent damage downstream. Such a strategy is deemed inadvisable. 7.5.2.2 Reducing vulnerability Given that the 1970 event surmounted a 150 m high ridge and still had the energy to destroy Yungay, it is considered most unlikely that measures could be engineered to protect habitation or infrastructure in the Río Santa valley. The most realistic method of managing the risks from Huascarán will probably be through the reduction of vulnerability to further aluviones. In the first instance, hazard zones need to be defined as recommended above in Section 7.5.1. It would then be necessary to look at the distribution and value of potential targets within these hazard zones to determine risk. To reduce people’s vulnerability will require a combination of education and enforced planning controls, directed through the agencies identified in the socio-economic study of the area (see Chapter 8). In this way, the most vulnerable areas could be kept from further development. Prediction of avalanches cannot be done far in advance and therefore continuous monitoring is required. It may then be possible to provide a warning prior to failure. It may be possible to monitor intrinsic causes to predict the time of failure for use in emergency management as discussed in the previous section (Crosta and Agliardi, 2002). Such information could be integrated within an appropriate response strategy that could include evacuation. Alternatively, sensors placed on the lower mountain slopes could be used to trigger alarms during an event to provide warnings to vulnerable communities or installations. Indeed, small as the warning of the 1970 event was, there was enough time for a few people to gain high

ground in Yungay and the Cañón del Pato hydropower plant at Huallanca was able to close safety gates. This approach would be most effective for the more distant vulnerable targets, such as Cañón del Pato HEP, where the warning time would be sufficient to allow them to respond. 7.6 Recommendations Uncertainties about the current levels of risk from Nevado Huascarán need to be addressed. Sequences of debris flow deposits in the Río Santa valley and the recent history of aluviones highlight the repeat nature of hazards from the mountain. Vulnerability may also be increasing as areas affected by former events are gradually resettled. A risk management strategy is needed that better identifies the nature of the hazards and areas that may be affected. The purpose here is to provide guidance as to how this may be achieved. In the first instance, rock mechanics, slope stability and avalanche processes can be considered and models calibrated from evidence of past events. Topographic and terrain parameters could be investigated to identify the potential starting zone and aluvión track, or tracks, and areas where secondary hazards may be triggered. Social and economic vulnerability can be identified and evaluated by surveying potential targets within the various hazard zones, such that acceptable levels of risk can be determined by the authorities and community representatives. Remediation of the mountain face is impractical, and therefore measures to reduce the vulnerability of targets are likely to be the most effective way of reducing risk. Monitoring can be undertaken as a predictive tool and combined with an appropriate response strategy to be implemented when the acceptable levels of risk are exceeded. Communication between the authorities and community, through local community groups and possibly even schools, will be an important part of the process so that people are aware of the general issues and remain informed about specific response strategies.

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8 SOCIO-ECONOMIC STUDY OF COMMUNITIES WITHIN THE AREAS OF LLANGANUCO AND SANTA CRUZ

8.1 Introduction A socio-economic study was carried out between July and September 2002 in the Department of Ancash, in the area between Llanganuco and Santa Cruz valleys in the districts of Yungay and Santa Cruz, respectively. Lima-based consultants Asociación SER (Association of Rural Education Services) undertook the research, under the guidance of staff from the Unit of Glaciology in Huaraz and Project Management of RGSL. The object of the study is to evaluate the perception of inhabitants and authorities have of their vulnerability with respect to natural threats (with emphasis on glaciers). The target of the exercise is to achieve the commitment of entities, organisations and authorities in the management of natural hazards and risks, and to communicate this information in order to create a culture of prevention. It is expected that this pilot exercise may be useful as a background to the introduction of the ‘risk management’ concept within all of the important agendas of the country. Asociación SER have produced a report (in English and Spanish) on the methods and findings of the study. A synthesis of the report is provided here. 8.2 Approach: risk perception The purpose of this survey is to analyse and evaluate the risk perception experienced by vulnerable inhabitants, institutions involved in the handling of risk management issues, and by authorities involved in policy decision-making processes. A commonly embraced approach to risk was adopted, associating risk, threat (i.e. hazard), and vulnerability in the following manner: Risk = hazard (threat) x vulnerability Therefore, the risk of a disaster may occur when one or more natural hazards take place in a vulnerable context (Maskrey, 1989). Emphasis here is placed on determining the perception of the local population to risk issues, specifically in respect to their vulnerability. Important vulnerability indicators are considered to be: �� nature and magnitude of hazard - physical

vulnerability

�� location in valley - spatial vulnerability �� organisational capacity - socio-economic

vulnerability �� purchasing power - socio-economic vulnerability �� psychological (e.g. identification with the place,

kinship) - socio-economic vulnerability 8.3 Methodology Information was obtained through the use of focus groups with local community members, and interviews with authorities, entities and key officers involved in risk management and civil defence. Focus groups were concentrated in the villages of Ranrahirca and Yungay, both in the district of Yungay, and at Cashapampa, in the district of Santa Cruz. Interview target groups within local government included mayors and councillors. Institutions represented included Huascarán National Park, INRENA, INDECI, and PNP - High Mountain Rescue Unit. Contacts were made in each area corresponding to the focus groups (Yungay, Ranrahirca and Santa Cruz), supplemented by other entities active within the broader survey area between Huaraz and Caráz. Work was conducted in four main stages: (a) An initial trip to the area to make contact with the authorities and to identify work areas; (b) The main period of fieldwork to conduct interviews with the authorities and focus groups with inhabitants of the selected valleys; (c) A final workshop with the authorities on 21st August in Huaraz, to consolidate ideas. Institutions represented at this seminar included the Mountain Institute in charge of institutional relations, INRENA, municipal councils, the National Park of Huascarán, INDECI (National Institute of Civil Defence), Concertation Table for Fight against Poverty, and CTAR Ancash, a Civil Defence representative for the region; (d) Office work, to undertake a desk study of maps and plans, literature and the existing census statistics (last obtained in 1993). Throughout the exercise, common concepts investigated were those of hazard, vulnerability and the attitude of the relevant communities and institutions with regard to each or their roles in the issue. Specific points investigated include: I. Hazard: �� Understanding of the concept of hazard or natural

threat �� Categorisation of hazard in the area of interest �� Perception of the location of hazard in the area �� Identification of the effects that a natural event

would cause, both human and material �� Feasibility of occurrence of natural threat event

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�� Summary of disaster cases caused by natural events

�� Summary of actions taken during and after the event

II. Vulnerability: �� Awareness of local population of exposure to

hazard (physical and socio-economic) �� Identification of the consequences of a natural

event affecting the population depending on its location

�� Identification of the measures to be taken to diminish the effects in case of an occurrence

�� Determination of the coverage and the condition of the services and infrastructure existing in the area

�� Identification of community-based organizations with related activity

�� Identification of social or economic liaisons, or other activities that relate the inhabitants of the area of interest

�� Reasons to accept or reject the proposals for a relocation in safe areas

III. Attitude: �� Identification of the Institutions, community-based

organizations or local government that work in the area

�� Activities developed by the previously identified entities

�� Ranking of the performance of these activities. �� Identification of the existing relations with the

identified entities and ranking of the liaison with them

�� Identification of the formal measures for the treatment of hazards

�� Identification of the key actors actively involved in those measures

�� Qualification of the treatment measures and performance of key actors

�� Determination of the ideal leaders for the treatment of threats

8.4 Summary of findings 8.4.1 Information from focus groups with local

inhabitants Discussion topics were tailored to each of the three focus groups, whilst retaining a general focus on perceptions of hazard, vulnerability and attitudes. In this way Asociación SER consultants were able to identify a commonality in the results as outlined below.

8.4.1.1 Concepts and perceived vulnerability Most participants know and can explain the meaning of hazard. They also know and can explain the relationship between hazard and risk, and they are aware that generally they are vulnerable to possible natural hazards;

“Simply, they are aware that they are going to suffer a disaster anytime; if it happened right now, may be a lot of people would escape and be safe due to their agility, many would be dead trying to escape and others would die with resignation. But that is something they had already thought about”. (Ranrahirca) “Mainly, the greatest risk are the aluviones or the avalanches since we are at the very foot of the highest “nevado” (Note: peak above snow line) of this country, the Huascarán, that’s the main risk” (Yungay)

Thus the awareness of vulnerability is at both the level of general exposure and in relation to specific threats. The risk of further aluviones from Nevado Huascarán is obviously a common concern, even though attitudes are split. On the one side, those with an active viewpoint are in favour of investing in work to address the threat; the other, the passive viewpoint, is evidenced by a fatalist feeling that their situation is part of a package, which offers work and housing in exchange for such risk. Both pragmatists and fatalists are aware that they are living side by side with the hazards. They feel they know well the hazard characteristics of these areas and they can identify accurately the areas affected by former aluviones and the timing of these events. Despite being able to recall the tragic history of the area in detail, often from first hand experience, the participants admitted to feeling safe where they live. 8.4.1.2 Response strategies Participants were in agreement with what action they would take in the event of another natural disaster. Most would chose to run to highlands.

“In our case, wherever we might be, we will always try to act as before, according to our vision and experience, we will try to reach highlands”. (Ranrahirca) “What we do in the first place, as we always do according to prior experiences lived before 1970, our main goal is to run to highlands”. (Yungay)

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When asked to be more specific about where exactly they should go, they were hesitant. When we asked if children would act the same way, they again were hesitant to answer, but they finally accepted that children were unlikely to respond in that same way alone. One of the participants mentioned how unpredictable reactions can be during a moment of panic. After this the group was questioned again about what attitude they would have in case of a hypothetical occurrence of a natural event:

“...but anyhow, there are many people that because of the panic, the fear, the anguish and the desperation they suffer in that moment, they may remain seated. Or other people who, trying to reach highlands would be running one over the other...” (Ranrahirca)

Others acknowledged that it is hard to know really what to do and where to go, since it is not known which the safe areas are for sure.

“...it all depends on the degree and amount and on the natural effect arising out of the avalanche. If it is minimal, the effect would be minimal, if the mass carried by the avalanche is bigger, the effect would be greater”. (Ranrahirca)

Also, in terms of preparedness, participants commonly acknowledged a perceived lack of effectiveness of their existing local community-based organisations. It seems that they have received no guidance on what to do, how to do it and where to go in the event of a disaster.

“...in every village... this is what is missing (local organisations)...that is why we are losing our values. In the old times... they did not have a theory but they put things into practice, the “minca”, the community, that is what is missing in our village... we lack practice. Just pure theory, there is no participation, no summoning, that is what is missing”. (Ranrahirca)

8.4.1.3 Resettlement Participants explained that the current inhabited area is a relocation area, identified by the State after the aluviones of the 1960s and 1970s.

“To make a reference, when the 60’s seism (earthquake) happened, the geologists came to see the whole area, to study it, and they said that all the area was... it was hazardous, it was an alluvial area. And that the city should not be built here, they recommended building

it near Carhuaz, in an area now called Pampas” (Yungay)

Relocation, they add, in these circumstances, must surely have been based on safe parameters. However, when past recollections of aluviones mentioned earlier by the participants were reintroduced to the discussion at this point, there was more than one that doubted those ‘safe parameters’. Some recalled a parallel episode in history when Yungaínos, after the tragedy that struck Ranrahirca in 1962, trusted that the Ayra mountain (a 150 m high hill between Huascarán and the previous position of Yungay) would protect them from Huascarán, although this was not the case. However, despite a lack of agreement regarding their perceived level of vulnerability, what was evident was the inhabitants’ resistance to move away from the area they currently were living in, since they accepted that hazard was part of their lives.

“...we have become used to our mountains, our valleys; we cannot move from our place, we don’t want to...” (Yungay)

Regarding the matter of safe parameters for a safe relocation, the indifference displayed by the authorities was criticised. First it seems that the authorities did not prevent the resettling of areas buried by the 1962 and 1970 aluviones, those very same areas that were classified out of bounds by the State; likewise, it is public knowledge that they have not done enough to stop migration to these areas. Second, they authorised the building of an educational centre in the surrounding areas of new Yungay, adjacent to the buried areas of the original village. A common view is that basic livelihood priorities overshadow the threat from natural hazards, such that repopulation of the aluvión affected areas is viewed as a necessary, and almost unconscious, action carried in plain view of the neighbours and authorities.

“After 1970...human settlements were forbidden so a reforestation was carried out and eucalyptus were planted. But then it was evident that the people had their agricultural needs, they needed to build their homes so they chose to break that law, it was necessary to change it. (Ranrahirca)

8.4.1.4 Attitudes towards risk management Participants felt they have a clear knowledge of the institutions present in the area, even though they argued that their activity is almost non-existent. They appear to feel detached from the activities of the authorities. There is also a high level of distrust and

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scepticism regarding the performance of the local authorities.

“...people have a bad image of their authorities. Why? Because these authorities work - as I have said before - behind people’s back. That is the greatest reason why the people are so unsatisfied, without knowing the things that their authorities do. That is the greatest mistake that the authorities are making.” (Ranrahirca)

As regards safety and prevention tasks:

“Maybe it could be made by means of the Municipality but unfortunately, as this gentleman has already said, on account of a bad management there is a great distrust, and may be a new resource will be given a wrong use. (Ranrahirca)

This criticism is also directed at the measures (viewed as far too few) previously undertaken by the local authorities.

“They made a scenario - Miss - that was worthless for everybody, because in the middle of an earthquake, tell me, will children go out orderly with their teacher to the plaza? Are the police going to be there with their car and the siren ready to go out? Tell me, here, the hospital will be ready to go out with its ambulance and the streets will be empty? ... but all the streets are going to be closed... They make a scenario, spend a lot of money and nothing is left for the people.” (Yungay)

8.4.2 Information from interviews with

organisations and authorities Key points arising from this activity are summarised below. �� There is positive interest in the issue of risk due to

natural hazards and concern about the seriousness of the issue. Partly the reason for the concern is the constant presence of the threat combined with the fact that most of the officials interviewed are also residents of the area and thus potential targets themselves. Despite the level of interest, the management of natural risks is not defined within civil management activity schedules. This omission is considered to be on account of the unpredictability of natural hazards, which makes them a remote issue for the everyday agenda.

�� A lack of action in dealing with the risk issue is

seen to be a consequence of post holders having

other responsibilities and priorities. Partly this is due to the exclusion of the issue within the activity schedules and budgets for local authorities as mentioned above. The minimal allocation of funds and personnel for the treatment of an activity not expressly described in the work schedules is to be expected. As a consequence any work undertaken tends to be insufficient and ineffective.

�� Due to the marginal treatment of natural risk issues,

a clear need to formalise work guidelines for inclusion within local development planning was identified by several organisations. It was thought that these would be best concentrated within schemes associated with local governments, who are in charge of almost all the potential victims of these natural threats.

�� Some complaints were voiced regarding the

manner in which the few risk management activities undertaken are conducted. They argued that there is a lack of effective training for personnel involved at all levels and a lack of allocation of effective resources. This demand for training was generally encountered, as evidenced by the concern of the inhabitants as well as interviewed representatives of the authorities.

�� It was commonly thought that there is a need to

review and modify the measures used to reduce risks from natural hazards, in order to tailor them to the particular local circumstances. In this point we find a higher degree of commitment in the population, presumably since they would be directly involved in the process, which in turn would improve the likelihood of compliance with preventive measures.

�� Important problems were detected in the

communication of information from the authorities to the community. Some stated that this was due to a lack of commitment on the behalf of the local population that were against or paid no attention to simulacrum activities. Others blamed a lack of means (material or economical) to make the available messages effective, whether through radio advertisements, civil meetings, or poster/flyer distribution. Whatever the media used, there appear to be problems. Radio broadcasts are the most common method of dissemination, but not all of the population away from the most densely populated areas can receive radio signals. Poster campaigns are also typically restricted to the towns.

�� Problems with communication combined with

perceived inadequate measures for the management of natural risks go some way to explaining the lack of participation by the local population that was frequently referred to these interviews. Irrespective of these points, other

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reasons for a lack of participation may be related to the fatalistic attitude identified in the community focus groups that would not otherwise exist if the culture was one of prevention.

�� There was cited a lack of technical and

management tools suitable for the development of risk reduction issues. In-depth technical tools in particular were mentioned, such as procedures for identifying and zoning vulnerable areas by type of threat, as well as the mapping of safety areas for planning purposes. This reflects the level of commitment given to the issue as highlighted earlier; without specific management remits and a lack of resources (financial, material and trained personnel) it is impossible to deal with the problem in an appropriate and effective manner, either though governmental channels or with non-governmental technical assistance. It was thought that the formalisation of risk issues within government is needed in order to develop activities, which in turn will drive the production of the necessary technical tools.

8.4.3 Information from the community risk

perception workshop Five key questions were posed to the participants in the workshops held in the villages of Yungay, Ranrahirca and Cashapampa, producing the following consensus answers and findings: a) What are the natural threats, ranked by degree of hazard and probability of occurrence? All the groups in Yungay and Ranrahirca had aluviones as their chief natural threat, with earthquakes (seisms) coming second or third. Torrential rain/mudslides/mountain landslides also featured high on the lists. The groups in Cashapampa also identified earthquakes as a principal threat. Aluviones were low on their list or not identified, and volcanoes featured. The greater concern about aluviones in Yungay and Ranrahirca compared to Cashapampa seemingly reflects the exposure of the former villages to such hazards from Nevado Huascarán. Although several styles of hazard within their environment were identified, the ranking of such threats by degree of hazard and probability shows some confusion. This appears to be caused by the distinction between the frequency and magnitude of events. It appears that the frequency of hazards is more important to them than magnitude. Frequent hazards such as annual seasonal rains are more feared and thus have a higher demand for management than high magnitude hazards such as aluviones. The focus group sessions already

identified that lessons learnt from high magnitude hazards are quickly forgotten on a geological timescale. It is, for example, 33 years, i.e. a generation, since the last major catastrophe affected the communities interviewed. It may also be probable that the lack of attention by the authorities and other key actors may be due to the same reason; they are not aware of the importance and scale of such matters. b) What are the main problems associated with this issue? Answers: 1. Lack of organization by authorities 2. Indifference of people to undertake responsibilities 3. Lack of a special budget to create those organisations required for risk management 4. Personnel with no training to undertake technical and planning responsibilities 5. Lack of implementation in public sectors to face this issue 6. Inadequate information 7. Lack of technical support to identify strategic locations for the relocation of new settlements c) What activities would help to solve these problems? Answers: 1. Summon people to create community-based organisations 2. Facilitate the full and active participation of people 3. Training of people in charge of all stages of the risk management process 4. Develop a programme of activities in association with the local population 5. Management of technical support and budgetary questions 6. Carry out surveys to find possible relocation sites 7. Formulation of a work plan on disasters d) Who are the key actors/practitioners in risk management? Answers: 1. Local authorities 2. Public sector in general 3. Community-based organizations 4. People 5. Civil defence e) Who are the possible leaders for the solution to these problems? Answers: 1. State 2. Civil defence 3. Regional government 4. Local government 5. Non-governmental organizations

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8.5 Conclusions Considering the answers regarding access to services, the role of institutions and authorities, and based on the absence of effective community-based organisations in those towns, it is evident that the people in the areas surveyed are vulnerable from a social and economic point of view. They lack the logistics and the capacity to respond in an organised manner to natural disasters; likewise, they do not have the necessary information, nor the institutional support needed to deal with this issue. It was also found that the lack of real support and permanent effective community-based organisations over time have contributed to the local fatalist feeling mentioned above. This is why the option of the majority in case of an aluvión, would be to run to the highlands; when there is lack of actual knowledge their instincts prevail. A national and regional agenda that does not consider the effective inclusion and treatment of natural risks in its development plans is an agenda lacking a vision of safe development, without sustainable awareness and a culture of prevention. 8.6 Recommendations It is important to standardise information to be communicated, as the knowledge regarding the risk issue is varied. Information to be communicated should be accurate, clear and made available to the authorities and to the inhabitants. The information should be communicated at every level and in all areas as part of an education plan on natural hazards and risks. It is important that this information is in the public domain. Relevant information that should be communicated includes: 1. The description of threats and hazards associated with natural phenomena in the area and in the region (characterisation and categorisation); 2. The description of the processes that trigger these natural threats (characterisation and its categorization); 3. The specification of safety measures, depending on the area and the potential hazards identified. Prevention and preparedness is preferable to disaster response, but this concept still needs to be incorporated in the national work agendas. There is an urgent need to develop technical procedures for risk assessment, monitoring, and emergency response plans. Risk zonation, including

the identification of safe areas for development, must be considered a priority. In order to achieve this goal, research studies need to be applied and implemented in association with key practitioners. Ranking of the risks will enable scarce resources to be directed towards the areas of highest priority first. One way of intensifying a communication and prevention campaign would be through local schools, since this is a proven communication channel influencing the family group. It is considered vital to dedicate resources and efforts to achieve an effective and adequate training in risk management issues. Training of technical practitioners is critical to enable them to assess hazards and risks accurately. Training should also be adequate for the intended recipients of the technical information, be it the authorities, community representatives, or others. The interest of the inhabitants needs to be captured. The acknowledgement by participants of this exercise of the unpredictable condition of natural hazards provides clues as to how this may be achieved. Inhabitants acknowledge the natural hazards associated with glaciers and they also identify with them because of their vulnerable condition. Due to the greater recurrence of different hazard types, however, they have other priorities. Increased education to raise awareness of the risks, combined with the natural interest to work with the unpredictable, could be strong elements towards accomplishing a commitment.

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9 SUMMARY Each chapter has been autonomous in that they have their own recommendations and/or conclusions. The following chapter will provide a summary of these sections. Working closely with staff from the Unit of Glaciology, INRENA, the history of glacial hazards and their management has been reviewed. Practical work to reduce the risks from glacial hazards was instigated following an outburst flood from Laguna Cojup in 1941, which killed 4,000 people. Of the variables affecting hazard from glacial lakes, volume of water is the easiest to modify. Consequently, lowering of lake levels has been a common form of remediation and 38 lakes have security works of various kinds. A failure from the ice-capped Huascarán Norte, triggered by an earthquake in 1970, killed 23,000 people. This well documented and tragic event gave renewed momentum to the issue of glacial hazards. With the privatisation of ElectroPerú in 1996, the country’s glacier management capacity was disbanded, but has been reformed as the Unidad de Glaciologia y Recursos Hidricos, within INRENA. A number of joint projects with international partners are underway. Raucolta Glacier was examined to test theories of lake development and early recognition. Digital photogrammetric analysis shows that the lower part of the glacier snout has been below the 2° threshold for supraglacial lake formation (cf. Reynolds, 2000) since at least 1948. However, ponds are draining through and/or beneath the moraine ridges rather than coalescing as a glacier-wide lake. Analysis of glacier morphology and other field evidence shows a stagnant zone of ice exhibiting surface lowering. Such areas have formed lakes in other areas. The absence of lake in this case suggests that other factors such as the permeability of the moraine may be important. Lagunas Safuna Alta and Safuna Baja were examined at the request of INRENA, to meet their priorities, and to assess the procedures for hazard and risk assessment for this project. On the 22nd of April 2002 a rock avalanche into Safuna Alta caused a 100 m high displacement wave, which over topped the 80 m moraine ridge. Although eroded, the moraine dam did not fail and Laguna Baja largely dissipated the flood. Field observations indicate that there is a high probability of further rock avalanches and modelling of the moraine-dam shows that it is close to the point of failure. The moraine dam cannot be expected to withstand a similar avalanche and displacement wave. Recommendations include the repair of two existing tunnels through the moraine-dam to prevent the lake level rising and possibly the construction of an additional tunnel at

the current waterline. Consideration is given to strengthening the moraine, through the injection of grout, although such techniques are untried in the Andes. It is further recommended that the landslide source area be monitored to record movement and, in particular, acceleration of movement. This would be done prior to and during any remedial works and should be linked to a response strategy that includes evacuation of villages and the Huallanca hydropower plant. Laguna Arhueycocha was studied to consider the procedures for hazard and risk assessment where partial remediation has taken place. As with Safuna, this site tests procedures for the current project and helps INRENA meet their priorities. Recession of the Arhueycocha Glacier has left the snout on steep rock at an angle where slab avalanches may cause displacement waves. Partial remediation, through creation of an open channel, has lowered the lake by 8 m, reducing the flood volume available. However, the open spillway is vulnerable to erosion from displacement waves. It is recommended that the moraine-dam be capped with a constructed embankment to protect against erosion and to raise the freeboard. The lake level should be further lowered by an amount determined by additional study. This site demonstrates the importance of remediation design and the danger of incomplete works exacerbating the risk. Laguna Llaca was investigated as an example of a lake where security measures were completed 25 years ago, to review the remedial works in light of any changes that may have taken place. The lower reaches of the glacier are in advanced stages of thermokarst decay, with a calving cliff developing up glacier. The 10 m freeboard provided by the constructed channel and dam are considered effective, but in light of the increasing volume of the lake and hence hazard, monitoring of the lake and adjacent slopes should take place. This site demonstrates the need for reassessment where physical conditions have altered. Similar changes elsewhere in the Cordillera Blanca are expected under the scenario of continued climatic warming. Nevado Huascarán was viewed, at a distance, at the request of INRENA to help with their planning and monitoring strategy. The mountain has been the repeated source of catastrophic rock avalanches or sturzstroms. The most notable event was the 1970 failure that destroyed Yungay and Ranrahirca with the loss of 23,000 lives. There are uncertainties as to the current levels of risk posed by Huascarán, although vulnerability is increasing as the avalanche path is gradually resettled. A risk management strategy needs to consider the physical processes and models calibrated from the evidence of past events. Social and economic vulnerability would also need to be

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examined through surveying potential targets within hazard zones, so that acceptable levels of risk can be determined by the authorities and communities. As remediation is impractical, reduction of vulnerability of targets is the most effective way to reduce risk. Monitoring may provide a predictive tool, to be combined with a response strategy implemented when acceptable risk levels are exceeded. Communication between the authorities and community are important, to keep people aware of the issues and response strategies. A socio-economic study was undertaken by Asociación SER in the districts of Yungay and Santa Cruz. The examination evaluated the perception of the inhabitants and authorities of their vulnerability to natural hazards, and in particular glacial hazards. The study concludes that the people are vulnerable from a social and economic point of view. They lack the logistics and capacity for organised respond to natural disasters, and neither have the information nor the institutional support to deal with the issue. The fatalist feeling of the people is linked to the lack of effective organisations in the community. The report recommends communication of accurate and clear information to the authorities and inhabitants. The information related should include the description of the hazards and the processes that trigger them, and the safety measures that can be specified. Prevention and preparedness is preferable to disaster response and, as such, the need for development of technical procedures for risk assessment, monitoring and emergency response plans is noted. The catastrophic events from Nevado Huascarán dominate perceptions, attitudes and policies to risk management. It is clear that people’s knowledge of hazards and perception of their current level of risk is particularly influenced by these events, rather than by sound scientific judgement based on the current situation. Whilst it is important to consider the risks from Nevado Huascarán, this situation should not distract from other potential hazards in the area. A revised hazard and risk assessment for the whole region is needed, as hazards may exist in areas previously considered safe. This is illustrated by the aluviόn from Laguna Palcacocha in March 2003. Prior to this aluviόn, the lake was considered as a low hazard by some people on account of the security works completed in 1974.

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REFERENCES Abdalati, W. and Krabill, W. B. 1999. Calculation of

ice velocities in the Jakobshaven Isbrae area using airborne laser altimetry. Remote Sensing Environment, 67:194-204.

Alean J. 1984. Untersuchungen uber Entstehungsbedingungen und Reichweiten von Eislawinen. VAW Mitteilung, Nr. 74.

Ames, A. 1998. A documentation of glacier tongue variations and lake development in the Cordillera Blanca, Peru. Zeitschrift für Gletscherkunde und Glazialgeologie, 34:1-36.

Ames, A. and Hastenrath, S. 1996. Diagnosing the imbalance of Glacier Santa Rosa, Cordillera, Peru. Journal of Glaciology, 42:212-218.

Benn, D. I., Wiseman, S. and Hands, K. A. 2000. Rapid Growth of a supraglacial lakes, Ngozumpa Glacier, Khumbu Himal, Nepal. In: Nakawo, M., Raymond, C. F. and Fountain, A. (eds.) Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., September 2000. IAHS publication, 264:177-185.

Benn, D. I., Wiseman, S. and Hands, K. A. 2001. Growth and drainage of supraglacial lakes on debris-mantled Ngozumpa Glacier, Khumbu Himal, Nepal. Journal of Glaciology, 47:626-638.

Braun, L. N., Weber, M. and Schulz, M. 2000. Consequences of climate change for runoff from Alpine regions. Annals of Glaciology, 31:19-30.

Broggi. J. A. 1943. La Desglaciacion Actual de los Andes del Peru. Boletin de la Sociedad Geologica del Peru, XIV/XV:59-90.

Browning, J. M. 1973. Catastrophic rock slide, Mount Huascaran, north-central Peru, May, 1970. American Association of Petroleum Geologists Bulletin, 57(7):1335-1341.

Clague, J. J. and Evans, S. G. 2000. A review of catastrophic drainage of moraine-dammed lakes in British Columbia. Quaternary Science Reviews, 19:1763-1783.

Clapperton, C. M. and Hamilton, P. 1971. Peru beneath its eternal threat. Geographical Magazine, 43(9):632-639.

Cluff, L. S. 1971. Peru earthquake of May 31, 1970: engineering geology observations. Bulletin of the Seismological Society of America, 61(3):511-533

Crosta, G. B. and Agliardi, F. 2002. How to obtain alert velocity thresholds for large rockslides. Physics and Chemistry of the Earth, 27(36):1557-1565.

Davis, M. E., Thompson, L. G., Mosley-Thompson, E., Lin, P. N., Mikhalenko, V. N. and Dai, J. 1995. Recent ice-core climate records from the Cordillera Blanca, Peru. Annals of Glaciology, 21:225-230.

Favey, E., Geiger, A., Gudmundsson, G. H. and Wehr, A. 1999. Evaluating the potential of an airborne laser-scanning system for measuring volume changes in glaciers. Geografiska Annaler, 81A:555-561.

Flotron, A. 1977. Movement studies on a hanging glacier in relation with an ice avalanche. Journal of Glaciology, 19:671-672.

Haeberli, W. and Beniston, M. 1998. Climate change and its impacts on glaciers and permafrost in the Alps. Ambio, 27:258-265.

Haeberli, W., Wegmann, M. and Vonder Muehull, D. 1997. Slope stability problems related to glacier shrinkage and permafrost degradation in the Alps. Eclogae Geologicae Helvetiae, 90:407-414.

Harbor, J. M. 1992. Application of a general sliding law to simulating flow in a glacier cross-section. Journal of Glaciology, 38:182-190.

Hastenrath, S. and Ames, A. 1995. Recession of Yanamarey Glacier in Cordillera Blanca, Peru, during the 20th-century. Journal of Glaciology, 41:191-196.

Hidrandina, S. A. 1988. Glacier Inventory of Peru. Publicacion Auspiciada por el Consejo Nacional de Ciencia y Tecnologia. 105 pp.

Huggel, C., Kääb, A., Haeberli, W. and Krummenacher, B. 2003. GIS-based models for glacier lake outburst hazards: evaluation and application for recent events in the Swiss Alps. Geophysical Research Abstracts, 5(1)36.

Kayastha, R. B., Takeuchi, Y., Nakawo, M. and Ageta, Y. 2000. Practical prediction of ice melting beneath various thicknesses of debris cover on Khumbu Glacier, Nepal, using a positive degree-day factor. In: Nakawo, M., Raymond, C. F. and Fountain, A. (eds.) Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., September 2000. IAHS publication, 264:71-81.

Kennett, M and Eiken, T. 1997. Airborne measurement of glacier surface elevation by scanning laser altimeter. Annals of Glaciology, 24:293-296.

Kirkbride, M. P. 1993. The temporal significance of transitions from melting from to calving termini at glaciers in the central Southern Alps of New Zealand. Holocene, 3:232-240.

Kirkbride, M. P. and Warren, C. R. 1999. Tasman Glacier, New Zealand: 20th-century thinning and predicted calving retreat. Global Planetary Change, 22:11-28.

Lomnitz, C. 1971. The Peru earthquake of May 31, 1970: Some preliminary seismological results. Bulletin of the Seismological Society of America, 61(3):535-542.

Margreth, S. and Funk, M. 1999. Hazard mapping for ice and combined snow/ice avalanches – two case studies from the Swiss and Italian Alps.

R7816.118


72

Cold Regions Science and Technology, 30:159-173.

Maskrey, A. 1989. The popular management of natural disasters. Vulnerability and mitigation studies. ITDG (Intermediate Technology).

Naito, N., Nakawo, M., Kadota, T. and Raymond, C. F. 2000. Numerical simulation of recent shrinkage of Khumbu Glacier, Nepal Himalayas. In: Nakawo, M., Raymond, C. F. and Fountain, A. (eds.) Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., September 2000. IAHS publication, 264:245-254.

Perla, R. I. 1980. Avalanche release, motion and impact. In: Colbeck, S. C. (ed) Dynamics of snow and ice masses. Academic Press, New York, 397-462.

Plafker, G. and Ericksen, G. E. 1978. Nevados Huascaran Avalanches, Peru. In: Voight, B. (ed.) Rockslides and avalanches 1, natural phenomena. Elsevier, 277-314.

Rana, B., Reynolds, J.M., Shrestha, A.B., Aryal, R., Pokhrel, A.P., and Budathoki, K. 1999. Tsho Rolpa, Rolwaling Himal, Nepal: a case history of ongoing glacial hazard assessment and remediation. Journal of Nepal Geological Society 20: 242.

Reynolds, J. M. 1992. The identification and mitigation of glacier-related hazards: examples from the Cordillera Blanca, Peru. In: McCall, G. J. H., Laming D. C. J and Scott, S. (eds.), Geohazards, London, Chapman & Hall, 143-157.

Reynolds, J. M. 1998. High-altitude glacial lake hazard assessment and mitigation: a Himalayan perspective. In: Maund, J. G. and Eddleston, M. (eds.) Geohazards in Engineering Geology. Geological Society, London, Engineering Geology Special Publications, 15:25-34.

Reynolds, J. M. 2000. On the formation of supraglacial lakes on debris-covered glaciers. In: Nakawo, M., Raymond, C. F. and Fountain, A. (eds.) Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., September 2000. IAHS publication, 264:153-161.

Reynolds, J. M., Dolecki, A. and Portocarrero, C. 1998. The construction of a drainage tunnel as part of glacial lake hazard mitigation at Hualcan, Cordillera Blanca, Peru. In J. G. Maund and M. Eddleston (eds.) Geohazards in Engineering Geology. Geological Society, London, Engineering Geology Special Publications 15:41-48.

Richardson, S. D. and Reynolds, J. M. 2000a. An overview of glacial hazards in the Himalayas. Quaternary International, 65/66:31-47.

Richardson, S. D. and Reynolds, J. M. 2000b. Degradation of ice-cored moraine dams:

implications for hazard development. In: Nakawo, M., Raymond, C. F. and Fountain, A. (eds.) Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., September 2000. IAHS publication, 265:187-197.

RGSL. 1998. Mangde Chhu Hydroelectric Project Technical and Economic Study Glaciological Review. Unpublished Report, Mold, U.K.

RGSL. 2003. Estidio de vulnerabilidad de la central hidroelectrica, Machupicchu. Unpublished Report, Mold, U.K.

Sakai, A., Takeuchi, N., Fujita, K. and Nakawo, M. 2000. Role of supraglacial ponds in the ablation process of a debris-covered glacier in the Nepal Himalaya. In: Nakawo, M., Raymond, C. F. and Fountain, A. (eds.) Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., September 2000. IAHS publication, 264:119-130.

Selby, M. J. 1993. Hillslope materials and processes. Oxford University Press, Oxford, 451pp.

Thompson, L. G. 1980. Glaciological observations from the tropical Quelccaya ice-cap, Peru. Journal of Glaciology, 25:69-84.

Thompson, L. G. 2000. Ice core evidence for climate change in the Tropics: implications for our future. Quaternary Science Reviews, 19:19-35.

Thompson, L. G., Mosley-Thompson, E., Henderson, K. A. 2000. Ice-core palaeoclimate records in tropical South America since the Last Glacial Maximum. Journal of Quaternary Science, 15:377-394.

Wilson, J., Reyes, L. and Garayar, J. 1995. Mapas Geologia de los Cuadrangulos de Pallasca, Tayabamba, Corongo, Pomabamba, Carhuaz y Huari. Instituto Geologico Minero y Metalurgico, Boletin 60.

Yamada, T. 1998. Glacier lake and its outburst flood in the Nepal Himalaya. Monograph No. 1. Data Centre for Glacier Research. Japanese Society of Snow and Ice, pp. 96.

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Appendix

Itinerary of RGSL staff

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ITINERY OF RGSL STAFF

DATE ACTIVITY 25 July JMR, SDR & APH depart UK and arrive in Lima, Peru (eve) 26 July Meeting with Ing. Prieto (Head of INRENA) to sign project agreement

Project management meeting with socio-economic sub-contractors, Asociación SER, & INRENA Meeting with company providing aircraft for over flight of Cordillera Blanca

27 July JMR, SDR & APH travel to Huaraz 28 July Acclimatisation day - visit to Cordillera Negra for panoramic views of Cordillera Blanca 29 July Field visit to Quebrada LLaca - review of glacial lake development and lake security works 30 July Fieldwork preparation, Huaraz. Team meeting to discuss fieldwork priorities. 31 July a.m. on standby for over flight of Cordillera Blanca - aborted due to bad weather

a.m. JMR & APH meeting with INRENA p.m. APH reviews archives at INRENA’s offices

1 August a.m. on standby for over flight of Cordillera Blanca - aborted due to bad weather p.m. APH reviews archives at INRENA’s offices

2 August a.m. JMR & APH over flight of Cordillera Blanca SDR - Huaraz

3 August JMR & APH travel to Laguna Safuna (over night at Pomabamba) SDR - Huaraz

4 August a.m. JMR & APH arrive at Laguna Safuna p.m. JMR & APH fieldwork at Laguna Safuna SDR - Huaraz

5 August JMR & APH fieldwork at Laguna Safuna SDR - Huaraz

6 August JMR & APH fieldwork at Laguna Safuna SDR - Huaraz

7 August JMR & APH fieldwork at Laguna Safuna SDR field visit to Pastoruri Glacier

8 August JMR & APH fieldwork at Laguna Safuna SDR - Field visit to Yanamarey and Pastoruri areas with INRENA staff

9 August JMR & APH fieldwork at Laguna Safuna SDR - INRENA offices, Huaraz

10 August JMR & APH depart Laguna Safuna to Pomabamba SDR - Field visit to Artesonraju glacier and Laguna Parón

11 August JMR & APH return to Huaraz SDR - Field visit to Artesonraju glacier and Laguna Parón

12 August Project meeting with Asociación SER 13 August JMR departs Huaraz for Lima

SDR & APH project meeting with sub-contractor César Portocarrero, Huaraz 14 August SDR & APH fieldwork preparation, Huaraz 15 August SDR & APH mobilise to Cashapampa and trek to Quebrada Raucolta 16 August SDR & APH fieldwork Raucolta Glacier 17 August SDR & APH fieldwork Raucolta Glacier 18 August a.m. SDR & APH fieldwork Raucolta Glacier

p.m. SDR & APH depart Raucolta for half way camp 19 August a.m. SDR & APH arrive at Cashapampa

p.m. preparation of logistics for trip to Santa Cruz valley 20 August SDR & APH Cashapampa to Llamacorrel in Santa Cruz valley; fieldwork during trek in 21 August SDR & APH Llamacorrel to Arhueycocha (Nev. Alpamayo base camp), fieldwork during trek in 22 August SDR & APH fieldwork, Arhueycocha glacial lake 23 August SDR & APH fieldwork, Arhueycocha glacial lake 24 August SDR & APH fieldwork, Arhueycocha glacial lake 25 August SDR & APH demob. to Cashapampa

eve - return to Huaraz 26 August SDR & APH field visit to viewpoints of Nevado Huascarán with INRENA staff 27 August SDR & APH at INRENA offices, Huaraz

eve - project meeting with César Portocarrero 28 August a.m. SDR project management meeting with César Portocarrero

p.m. SDR & APH demob. to Lima 29 August a.m. visit to National Geographic Institute and Peruvian Airforce for aerial photographs

eve. SDR & APH depart Lima, Peru 30 August eve. SDR & APH arrive UK

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General notes

R7816.115


GENERAL NOTES 1. Any assessments made in this report are based on the ground conditions as revealed by trial pits and boreholes, together with the results of any field or laboratory testing carried out and/or, where appropriate, other relevant data which may have been obtained for the sites including previous site investigation reports and information supplied by the Client. There may be particular conditions relating to the site which may not have been revealed by the investigation and which have not been taken into account in the report. The assessment may be subject to amendment consequent to additional information becoming available. 2. Where the data available from previous site investigation reports supplied by the Client have been used, it has been assumed that the information is correct. No responsibility can be accepted by Reynolds Geo-Sciences Ltd for inaccuracies within the data supplied. 3. While an opinion may have been expressed within this report on possible configurations of strata between or beyond trial pits or borehole locations, or on the possible presence of features based on either visual, verbal or published evidence, this is for guidance only and no liability can be accepted for the accuracy. 4. Comments on groundwater conditions are based on observations made at the time of the investigation unless otherwise stated. It should be noted that groundwater levels vary due to seasonal or other effects. 5. The copyright in this report and other plans or documents prepared by Reynolds Geo-Sciences Ltd is vested in us. No such report, plan or document may be reproduced, published or adapted without our written consent. Complete copies only of this report may be made and distributed by the Client as an expedient in dealing with matters related to its commission. 6. This report has been prepared and compiled in the context of proposals related to this specific commission and should not be used in a differing context. New information, improved practices and legislation may necessitate amendment to the report in whole or in part after its submission. Thus, with any changes in circumstances or after the expiry of one year from the date of this report, the report should be referred to Reynolds Geo-Sciences Ltd for re-assessment and, if necessary, re-appraisal, at a cost defined by the Schedule of Fees in force at the time of the re-appraisal. 7. This report is provided for use only by the Client and is confidential to him/her and his/her professional advisers. No responsibility whatsoever for the contents of the report will be accepted to any other organisation other than the Client's. 8. The response of the ground to differing physical forces can be highly variable. The interpretation of these responses in this report is based on our experience in similar conditions. The fact that due to highly variable ground conditions the interpretation may be found to be at variance with direct methods of investigation has to be accepted when using any remote sensing techniques.

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