1-Relationship between Landslides, Geologic Structures

Journal of Earth Science and Engineering 2 (2012) 317-327

Relationship between Landslides, Geologic Structures,

and Hydrothermal Alteration Zones in the

Ohekisawa-Shikerebembetsugawa Landslide Area,

Hokkaido, Japan

Hiroyuki Maeda1, Takashi Sasaki2, Kazuyuki Furuta3, Katsuhiro Takashima4, Akihiro Umemura5 and Masanori

Kohno6

1. Sapporo Technology Professional Training College, Sapporo 007-0895, Japan

2. Earth Consultant UEYAMA Co., Ltd., Sapporo 060-0032, Japan

3. Shin-Nikken Consultant Co., Ltd., Tokyo 133-0057, Japan

4. Takashima Land and Buildings Investigator Office, Nagano 399-8102, Japan

5. Japan Foundation Engineering Co., Ltd., Osaka 530-0037, Japan

6. Graduate School of Engineering, Tottori University, Tottori 680-8552, Japan

Received: April 27, 2012 / Accepted: May 14, 2012 / Published: June 20, 2012.

Abstract: This paper elucidates the relationship between landslides, geologic structures, and hydrothermal alteration zones based primarily on X-ray powder diffraction and uniaxial compressive strength tests on weakly weathered and hydrothermally altered rocks from the Ohekisawa-Shikerebembetsugawa landslide area in Teshikaga Town, Hokkaido, Japan. The OHS (Ohekisawa slide) occurred on a dip slope of sedimentary rocks from the Upper Miocene Shikerepe Formation within a homocline, and also on weathered and hydrothermally altered rocks within the boundary area between the hydrothermal smectite zone and smectite-bearing mordenite zone. The SHS (Shikerebembetsugawa slide) occurred on a dip slope of sedimentary rocks from the Upper Miocene Hanakushibe Formation within wavy folds and was also controlled by a cap rock of Teshikaga Volcano Somma Lava. The SHS occurred also on weathered and hydrothermally altered rocks within the boundary area between the hydrothermal smectite zone and smectite-bearing laumontite zone. The mechanical properties of smectite, smectite-bearing mordenite, and smectite-bearing laumontite zone weakly weathered rocks indicate that they are very weak, soft rocks. These landslides are regarded as HAZLs (hydrothermal alteration zone landslides). The hydrothermal alteration yielding smectite is thus closely related to these two ancient landslides, suggesting that the potential for HAZLs within a hydrothermal area can be assessed based on the swelling clay mineral-bearing hydrothermal alteration types, dip slope, and cap rock. Key words: HAZL (hydrothermal alteration zone landslide), swelling clay mineral-bearing hydrothermal alteration zone, weathered and hydrothermally altered soft rock, dip slope, cap rock.

1. Introduction

The existence of swelling clay minerals in slip

surface clays in landslides is one of the main causes of

reactivation-type landslides [1]. Although DZLs

Corresponding author: Hiroyuki Maeda, doctor, emeritus

professor, main research field: landslide science. E-mail: [email protected], [email protected].

(diagenetic zone landslides) and HAZLs

(hydrothermal alteration zone landslides), based on

geological landslide classification, have soft or hard

bedrock, and are induced by earthquakes, they operate

by the swelling of clay minerals in slip surface clays,

as well as a rise in underground water pressure during

heavy rains, long spells of rainy weather or the spring

DAVID PUBLISHING

D

Relationship between Landslides, Geologic Structures, and Hydrothermal Alteration Zones in the Ohekisawa-Shikerebembetsugawa Landslide Area, Hokkaido, Japan

318

thaw. HAZLs are defined as landslides that occur

within hydrothermal alteration zones formed by

volcanic-hydrothermal systems over geologic time

and historic period [2-5]. For instance, HAZLs in

Japan include those at the Asamushi Hot Spring and

Hakkoda in Aomori Prefecture, Onikobe and Naruko

Hot Springs in Miyagi Prefecture, Manza and

Kumaike in Gunma Prefecture, Mt. Sounzan and

Owakudani in Kanagawa Prefecture, Myoban in Oita

Prefecture, etc. [6-8]. These HAZLs occurred mainly

within acid hydrothermal alteration zones formed by

fumarolic gases derived from active acid hydrothermal

systems. Heavy rains accompanying the approach of a

typhoon led to the occurrence of the 2001 Manza

Slide and Kumaike Failure-Flow within neutral and

acid hydrothermal alteration zones formed by the

hydrothermal systems of the active Kusatsu-Shirane

volcano [8]. In contrast, HAZLs occurring on

weathered and hydrothermally altered rocks, which

were formed mostly by ancient neutral hydrothermal

systems of the Upper Miocene Ikutawara and Yahagi

Formations of the Ikutahara area in Engaru Town, and

the Kanehana area in Rubeshibe Town, Kitami City,

northeastern Hokkaido, Japan, from the Late Miocene

to the Early Pliocene, are closely related in space to

interstratified illite/smectite mineral and smectite zones

that are characterized by swelling clay minerals, and

swelling clay mineral-bearing zeolite zones, as well as

kaolin mineral, illite, and K-feldspar zones [2, 9-13]. In

addition, HAZLs took place within hydrothermal

smectite zone or smectite-bearing mixed-layer

mimeral zone along the Median Tectonic Line in

Shikoku, Japan [14, 15].

The strength of fresh and altered rocks, including

hydrothermally altered or weathered rocks, is

generally evaluated based on their uniaxial

compressive strengths. They are divided into hard

rocks with uniaxial compressive strengths greater than

25 MPa and soft rocks that can bear less than 25 MPa

in a forced-dry state. The uniaxial compressive

strength test, in particular, for weakly weathered and

hydrothermally altered rocks taken from outcrops or

floats in a hydrothermal field is effective to estimate

mechanical properties of landslide bedrocks and

bodies in weathered and hydrothermally altered

rockslides.

Teshikaga Town is situated in eastern Hokkaido,

Japan (Fig. 1). A number of studies have examined

landslides in this town, including papers by Maeda et

al. [5, 16-18]. From the Middle Miocene to the Early

Pleistocene, the Sattomonai-Okushunbetsu area in the

western part of the town (Fig. 1) was subject to intense

terrestrial volcanic-hydrothermal activity [19, 20]. Two

ancient landslides have been identified, based on

topography, in the southern part of the Okushunbetsu

area (Figs. 1 and 2). These ancient landslides have

been tentatively named the OHS (Ohekisawa Slide)

and SHS (Shikerebembetsugawa Slide) (Fig. 2). The

OHS is 350 m wide and 410 m long, whereas the SHS

is 175-450 m wide and 595 m long (Table 1).

The purpose of this study is to clarify the

relationship between HAZLs, geologic structures, and

hydrothermal alteration zones in the

Ohekisawa-Shikerebembetsugawa landslide area.

2. Methods and Equipment

The relationship between HAZLs, geologic

structures, and hydrothermal alteration zones was

examined based on an aerial photograph interpretation,

a 1:5,000-scale topographical and geological mapping,

and an XRD (X-ray powder diffraction) and uniaxial

compressive strength tests on weakly weathered and

hydrothermally altered rocks from the southern part of

the Okushunbetsu area.

Weakly weathered and hydrothermally altered

rocks were collected from the ground surface. The

modes of occurrence of these altered rocks were

examined in the field, and the hydrothermal alteration

minerals in the rocks were determined primarily by

the XRD test. Opal-CT was determined based on the

XRD patterns obtained by Jones et al. [21]. Clay

minerals in the rocks were identified from the


319

Nakajim a

Lake Kutcharo

Biruw a

Teshikaga

M t. Pekereyam a732.3

581

573

M t. Shikerepeyam a

M t. Nichieizan

Shibecha Tow n

M t. Ikurushibeyam a729

Fig. 2

0 4 km

N

Sattom onai

O kushunbetsu

Tow n

M ashu

Hokkaido

Sea of O khotsk

JAPAN

145˚E140˚E

130˚E

40˚N

35˚N

40˚N

35˚N

135˚E

45˚N

RUSSIA

C HINA

NO RTH

KO REA

SO UTH

KO REA

45˚N

25˚N125˚E200 km0

Teshikaga Tow n

Fig. 1 Location map of the Sattomonai-Okushunbetsu area in Teshikaga Town, eastern Hokkaido, Japan.

・513

・476

・328

・432

・425

573・

・377

・485

・348

・351

・390

・375

・581

・408

・305

・246

・294

・345

479・

347・

M t. Om onaiyam a

Route 241

OHS

1 km0

L E G E N D

O HS：O hekisaw a Slide

SHS：Shikerebem betsugaw a Slide

SHS

M t. Shikerepeyam a

M t. Nichieizan

N

Fig. 2 Two ancient landslide areas in the southern part of the Okushunbetsu area. The topographical map is part of a 1:25,000 map of Pekereyama from the Geographical Survey Institute of Japan.


320

Table 1 Analysis of ancient landslides in the southern part of the Okushunbetsu area.

Items OHS SHS

Total length (m) 410 595

Width (m) 350 175 (foot)-450 (main body)

Angle of slope 10-20° 10-25°

Bedrock geology Shikerepe formation Coarse tuff and tuffaceous medium sandstone

Hanakushibe formation Fine tuff, mudstone, and lapilli tuff

Geological structures Dip slope Dip slope on the whole and cap rock of lava

Hydrothermal alteration zone Smectite and smectite-bearing mordenite zones Smectite and smectite-bearing laumontite zones

diffraction patterns of untreated and ethylene

glycol-treated samples. XRD was performed using a

Rigaku RAD-3R diffractometer (30 kV, 20 mA)

equipped with a Cu tube, an Ni filter, a 0.3-mm

receiving slit, and 1° divergence and scattering slits.

Rock samples for uniaxial compressive strength

tests were taken using a drilling machine. The

specimens were 50 mm in diameter and cut to 100

mm lengths using a diamond cutter. The uniaxial

compressive strength tests were performed on core

specimens in a forced-dry state, after drying in an

electric oven at a temperature of 60 ± 3 °C for 4 days

or more to achieve a constant mass [13].

3. Geologic Setting

The Teshikaga district is within the inner belt of the

Kurile arc [22]. The geology of this district was

described mainly by Maeda et al. [20, 23-25]. The

geology consists mainly of Neogene and Quaternary

Systems, as well as Neogene and Quaternary intrusive

rocks. The Neogene System can be divided, in order

of ascending stratigraphy, into the Middle Miocene

Ikurushibe Formation, the Upper Miocene

Oteshikaushinai, Hanakushibe, and Shikerepe

Formations, and the Upper Pliocene Ikurushibeyama

Lava and Shikerepeyama Lava [23-26]. The

Quaternary System can be subdivided, in ascending

stratigraphic order, into the Shikerepempetsu

Formation, Pekereyama Lava, Teshikaga Volcano

Somma Lava, higher fluvial terrace deposits, lower

fluvial terrace deposits, talus deposits, landslide

deposits, and alluvial river deposits (Table 2).

Neogene and Quaternary intrusive rocks are chiefly

composed of andesite dikes, with lesser basalt and

rhyolite dikes [24]. These dikes are generally affected

by hydrothermal alteration and mineralization. K-Ar

ages of 2.43 ± 0.45 and 2.3 ± 0.8 Ma for the andesite

dikes [24] are believed to indicate the time of the

hydrothermal alteration and mineralization. The

Neogene formations and the Lower Pleistocene

Shikerepempetsu Formation underwent extensive

hydrothermal alteration and mineralization during the

Pliocene to Early Pleistocene epoch [19, 20]. The rock

facies of the Neogene and Lower Pleistocene

formations related to landslides in the

Sattomonai-Okushunbetsu area are as follows:

The Oteshikaushinai Formation is chiefly

composed of alternating andesitic and dacitic lapilli

tuff, tuff breccia, and tuff, with basal tuffaceous

conglomerate, sandstone, and mudstone;

The Hanakushibe Formation conformably

overlies the Oteshikaushinai Formation and is chiefly

composed of mudstone, and alternating fine sandstone

and tuff with andesitic tuff breccia and lapilli tuff;

The Shikerepe Formation conformably overlies

the Hanakushibe Formation and is chiefly composed

of andesitic and dacitic volcaniclastic rocks,

tuffaceous sandstone and mudstone, and dacitic

welded tuff;

The Ikurushibeyama Lava unconformably overlies

the Shikerepe Formation and is chiefly composed of

andesitic lava, volcanic breccia, and tuff breccia.

Pekereyama Lava is chiefly composed of basaltic

lava and has not suffered hydrothermal alteration [24].

Teshikaga Volcano Somma Lava is chiefly

composed of basaltic and andesitic lavas and volcanic

breccia and has also not suffered hydrothermal

alteration.


321

Table 2 Stratigraphy and volcanic-hydrothermal activity in the Sattomonai-Okushunbetsu area. Modified from Ref. [20].

Geologic time

Stratigraphy Rock facies of clastic rocks and extrusive rocks and extrusion ages

Hydrothermal alteration and mineralization ages

Holocene Pleistocene

Alluvial river deposits Gravel, sand, silt, and clay

Landslide deposits Rubble, sand, silt, and clay

Talus deposits Rubble, sand, silt, and clay

Lower fluvial terrace deposits Gravel, sand, silt, and clay

Higher fluvial terrace deposits Gravel, sand, silt, and clay Teshikaga Volcano Somma Lava

Basaltic and andesitic lavas, and tuff breccia 2.2 Ma Taiho (Kanehana) illitization 2.3 Ma Shikerepeyama natroalunitization 2.4 Ma Tobetsu Au and Ag mineralization

Pekereyama Lava Basaltic lavas (1.84 Ma)

Shikerepempetsu Formation Conglomerate, sandstone, mudstone, and dacitic volcaniclastic rocks (2.3 Ma)

Pliocene Shikerepeyama Lava Dacitic lavas (rhyolite: 2.63 & 2.81 Ma)

3.2-3.8 Ma Akan Au and Ag mineralization

Ikurushibeyama Lava Andesitic lavas and volcaniclastic rocks (2.61 & 2.73 Ma)

Late Miocene

Shikerepe Formation Andesitic and dacitic volcaniclastic rocks, sandstone, and mudstone

Hanakushibe Formation Mudstone and andesitic volcaniclastic rocks

Oteshikaushinai Formation Conglomerate and andesitic and dacitic volcaniclastic rocks (7.9-8.2 Ma)

Middle Miocene

Ikurushibe Formation Andesitic and dacitic lavas and volcaniclastic rocks (13.0 Ma)

The geologic structures of the Neogene formations

in the study area (Fig. 3) are as follows:

An NW-SE trending anticline can be mapped in

the lower reaches of Oteshikaushinaisawa Creek and

the Hanakushibegawa River in the northwestern part

of the study area (Fig. 3). An ENE-WSW trending

syncline leads to folds in the rocks in the middle

reaches of the Hanakushibegawa River in the western

part of the study area (Fig. 3), and an NNW-SSE

trending anticline leads to folds in the rocks in the

middle reaches of the Shikerebembetsugawa River in

the southeastern part of the study area (Fig. 3). Folds

with wavelengths of several hundred meters and

ENE-WSW fold axes are common in the middle

reaches of the Shikerebembetsugawa River in the

southern part of the study area (Fig. 3). Comparable

folds with NNE-SSW and ENE-WSW axes are

mapped in the upper reaches of the

Shikerebembetsugawa River in the southwestern part

of the study area (Fig. 3);

The Shikerepe Formation in the northeastern part

of the study area is characterized by an NNW-SSE to

NW-SE striking homocline and with dips less than

10° toward the NE (Fig. 3);

The faults are aligned in NE-SW, NNE-SSW,

and NW-SE directions in the study area (Fig. 3).

Hydrothermal alteration minerals identified in the

study area include quartz, opal-CT, K-feldspar, albite,

chlorite, illite, interstratified illite/smectite minerals,

interstratified chlorite/smectite minerals, smectite,

nacrite, dickite, kaolinite, analcite, laumontite,

heulandite-clinoptilolite series minerals, mordenite,

chabazite, stilbite, calcite, alunite, minamiite,

natroalunite, and pyrite.

Hydrothermal alteration can be zoned according to the

occurrence of characteristic minerals such as silica

minerals, feldspars, clay minerals, zeolites, and alunite.

The hydrothermal alteration zones have been

identified in the study area, based on mineral

assemblage, propylitic, laumontite, heulandite,

analcite, mordenite, clinoptilolite, stilbite, smectite,

interstratified illite/smectite mineral, illite, K-feldspar,

and alunite-quartz zones (Table 3). These alteration

zones are oblique to bedding planes within the

formations described previously.

The distribution of landslide-related hydrothermal


322

Pleistocene- H olocene Series

L E G E N D

Alluvial river deposits

Landslide deposits

Talus deposits

Low er fluvial terrace deposits

Higher fluvial terrace deposits

Teshikaga Volcano Som m a Lava

D ikes

U pper M iocene Series

Shikerepe Form ation

Hanakushibe Form ation

Pliocene Series

Shikerepem petsu Form ation

Shikerepeyam a Lava

O teshikaushinaiForm ation

G ravel, sand, silt, and clay

Rubble, sand, silt, and clay

Rubble, sand, silt, and clay



Basaltic and andesitic lavas

M udstone and andesitic

C onglom erate, sandsone,

Dacitic lavas

Rhyolite

Andesite

Basalt

volcaniclastic rocks,

m udstone, and dacitic

dacitic volcaniclastic rocks

Strike and dip of strata

Anticlinalaxis

Synclinal axis

Faults

O H S：O hekisaw a Slide

SH S：Shikerebem betsugaw a Slide

▲ ▲

V V

・∟

V・

V・

∟ ∟

Andesitic and dacitic

C onglom erate and andesitic and

and tuff breccia

volcaniclastic rocks

sandstone, and m udstone

volcaniclastic rocks

Al

La

Lr

Hr

Td

Te

Sh

Ha

Sm

Sy

O t

V

V

・

・

30

10

20

20

10

5

5

8

910

∟ ∟ ∟ ∟ ∟ ∟

∟ ∟ ∟ ∟ ∟ ∟ ∟

∟ ∟ ∟ ∟ ∟ ∟ ∟ ∟

∟ ∟ ∟ ∟ ∟ ∟ ∟ ∟ ∟

∟ ∟ ∟ ∟ ∟ ∟ ∟ ∟

∟ ∟ ∟ ∟ ∟ ∟

∟ ∟ ∟ ∟

∟

∟

∟ ∟

▲ ▲ ▲ ▲ ▲

▲

▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲

▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲

▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲

▲ ▲

▲ ▲ ▲ ▲

▲ ▲ ▲ ▲

▲ ▲ ▲

▲ ▲

▲

▲

▲ ▲

▲ ▲ ▲ ▲

▲ ▲ ▲

▲ ▲

▲

▲

▲

V・

V・

V・

V・

V・

V・

∟∟

∟

∟

∟∟

∟

・・

・

・

・・

・

V V

V

V

V V V V

V

V V V V V V

V V V V V

V V V V

V V V

V V V

V V V

V V V

V V V

N

0 1 km

M t. Shikerepeyam a

M t. Nichieizan

La

Al

Hr

Hr

Hr

Lr

Hr

Td

Sy

Sy

Sh

Ha

Sm

Ha

Sh

Al

5

SHS

O HS

O t

Hr

18

19

7

Te

La

Ha

Sh

Ha

O t

Sm

Sh

Sh

Fig. 3 Geological map of the southern part of the Okushunbetsu area. Modified from Refs. [24, 27-29].

alteration zones, and the mineral composition and

uniaxial compressive strengths of their alteration zone

rocks documented in the study area are as follows:

The laumontite zone is widely distributed in the

western part of the study area (Fig. 4) and its rocks

consist mainly of laumontite with lesser amounts of

smectite, quartz, albite, illite, chlorite, calcite, and

pyrite (Table 3). The uniaxial compressive strengths

of laumontite zone weakly weathered tuffaceous

conglomerates from the Ikurushibe Formation in a

forced-dry state range from 84.07 to 91.10 MPa, with

an average of 87.59 MPa, whereas the strengths of

smectite-bearing laumontite zone weakly weathered

lapilli tuff and fine tuff from the Hanakushibe

Formation are 6.18 and 12.91 MPa, respectively

(Table 4).

The mordenite and clinoptilolite zones are widely

distributed in the eastern and southern parts of the study

area and occur locally in the western part (Fig. 4). The

mordenite zone rocks consist mainly of mordenite

with lesser amounts of opal-CT, quartz, smectite,

clinoptilolite, and pyrite (Table 3). The uniaxial

compressive strengths of smectite-lacking mordenite

zone weakly weathered fine tuffs from the Shikerepe

Formation in a forced-dry state range from 17.95 to

44.64 MPa, with an average of 27.37 MPa, whereas

smectite-lacking mordenite zone weakly weathered

pumice tuffs from the Shikerepe Formation have

strengths ranging from 7.24 to 10.62 MPa, with an

average of 8.93 MPa. The uniaxial compressive

strengths of smectite-bearing mordenite zone weakly

weathered pumice tuffs from the Shikerepe Formation

range from 14.00 to 19.69 MPa, with an average of

17.15 MPa (Table 4).

The smectite zone occurs mainly in the northeastern

and southwestern parts of the study area (Fig. 4), and

the rocks consist mainly of smectite with lesser

amounts of opal-CT, quartz, and pyrite (Table 3). The

uniaxial compressive strengths of smectite zone

weakly weathered fine tuffs from the Hanakushibe

Formation in a forced-dry state range from 6.28 to

7.94 MPa, with an average of 7.11 MPa, and smectite

zone weakly weathered fine tuff from the Shikerepe

Formation has a strength of 10.67 MPa (Table 4).

4. Results and Considerations

The bedrocks of the OHS in the southern part of the


323

Table 3 Mineral assemblages of hydrothermal alteration zones.

Alteration zone

Mineral

Sme zone

Stb zone

Cpt zone

Mor zone

Hul Zone

Anl zone

Lmt zone

Prop zone

Ilt/Smezone

Ilt zone

Kfs zone

Alu-Qz zone

Quartz

Opal-CT

K-feldspar

Albite

Illite

Chlorite

Int. Ilt/Sme

Smectite

Stilbite

Clinoptilolite

Mordenite

Heulandite

Chabazite

Analcite

Laumontite

Calcite

Alunite

Natroalunite

Minamiite

Pyrite

Major occurrence

Minor occurrence

Int. Ilt/Sme: interstratified illite/smectite minerals; Sme zone: smectite zone; Stb zone: stilbite zone; Cpt zone: clinoptilolite zone;Mor zone: mordenite zone; Hul zone: heulandite zone; Anl zone: analcite zone; Lmt zone: laumontite zone; Prop zone: propylitic zone; Ilt/Sme zone: interstratified illite/smectite mineral zone; Ilt zone: illite zone; Kfs zone: K-feldspar zone; Alu-Qz zone: alunite-quartz zone.


324

L E G E N D

Faults

Illite zone

Least altered zone

Analcite zone

Propylitic zone

O utline of ancient landslide

Alunite-quartz zone

Sm ectite zone

M ordenite and clinoptilolite zones

Laum ontite zone

Int. Ilt/Sm e zone

Int. Ilt/Sm e zone：Interstratified illite/sm ectite m ineral zone

Heulandite and stilbite zones

O HS：O hekisaw a Slide

SHS：Shikerebem betsugaw a Slide

M t. Shikerepeyam a

M t. Nichieizan

N

1 km0

O HS

SHS

Fig. 4 Hydrothermal alteration map of the southern part of the Okushunbetsu area.

Okushunbetsu area are weathered and hydrothermally

altered and are composed of coarse tuff and tuffaceous

medium sandstone of the Upper Miocene Shikerepe

Formation. The landslide has a dip slope structure

with an NNW-SSE strike and a dip direction of 7°E

(Fig. 3 and Table 1). The scarp of the OHS consists of

an N-S striking andesite dike that is 125 m wide and

325 m long (Fig. 3). The bedrock under the upper part

of the landslide body is composed of smectite-bearing

mordenite zone rocks, whereas that under the middle

and lower parts of the landslide body is composed of

smectite zone rocks (Fig. 4 and Table 1). As described

previously, the uniaxial compressive strengths of

smectite-bearing mordenite zone weakly weathered

pumice tuffs from the Shikerepe Formation range

from 14.00 to 19.69 MPa, with an average of 17.15

MPa and smectite zone weakly weathered fine tuff

from the Shikerepe Formation has a strength of 10.67

MPa (Table 4). These bedrocks, therefore, are

classified as soft rocks.

The SHS bedrock also consists of weathered and

hydrothermally altered rocks, mainly fine tuff,

mudstone, and lapilli tuff of the Upper Miocene

Hanakushibe Formation. The landslide has a dip slope

structure as a whole because the bedrocks have a

synclinal structure on an ENE-WSW axis; the

bedrocks under the upper and middle parts of the

landslide body dip 10° toward the SE, whereas those

of the lower part dip 0-5° toward the NW (Fig. 3). The

landslide scarp consists of a cap rock of Teshikaga

Volcano Somma Lava. The bedrocks under the upper

part of the landslide body are composed of smectite

zone rocks, whereas those under the middle and lower

parts are composed of smectite-bearing laumontite

zone rocks (Fig. 4 and Table 1). As described

previously, the uniaxial compressive strengths of

smectite-bearing laumontite zone weakly weathered

lapilli tuff and fine tuff from the Hanakushibe

Formation in a forced-dry state are 6.18 and 12.91

MPa, respectively, and those of smectite zone weakly

weathered fine tuffs from the Hanakushibe Formation

range from 6.28 to 7.94 MPa, with an average of 7.11

MPa. These, therefore, are also classified as soft

rocks.

Both of the landslides, therefore, occurred

mechanically on very weak rocks consisting of

smectite-bearing weathered and hydrothermally

altered soft rocks such as smectite, smectite-bearing

mordenite, and smectite-bearing laumontite zone

rocks.

The OHS occurred on weathered and

hydrothermally altered rocks within the boundary area

between the smectite zone and the smectite-bearing

mordenite zone, whereas the SHS occurred on

weathered and hydrothermally altered rocks within the

boundary area between the smectite and

smectite-bearing laumontite zones. This circumstance

has been reported in only a few other cases such as the


325

Table 4 Uniaxial compressive strength of hydrothermal alteration zone rocks in a forced dry-state, dried in an electric oven at 60 ± 3°C, in the southern part of the Okushunbetsu area.

Hydrothermal alteration zone Formation Rock facies N qu (MPa)

Smectite-lacking laumontite zone Ikurushibe Fm. Weakly weathered tuffaceous conglomerate 1 84.07 Smectite-bearing laumontite zone Smectite-bearing laumontite zone Smectite-bearing laumontite zone

Ikurushibe Fm. Hanakushibe Fm. Hanakushibe Fm.

Weakly weathered tuffaceous conglomerate Weakly weathered fine tuff Weakly weathered lapilli tuff

1 1 1

91.10 12.91 6.18

Smectite-lacking mordenite zone Smectite-lacking mordenite zone

Shikerepe Fm. Shikerepe Fm.

Weakly weathered fine tuff Weakly weathered pumice tuff

35 2

17.95-44.64 (Avg. 27.37) 7.24-10.62 (Avg. 8.93)

Smectite-bearing mordenite zone Shikerepe Fm. Weakly weathered pumice tuff 20 14.00-19.69 (Avg. 17.15) Smectite zone Smectite zone

Shikerepe Fm. Hanakushibe Fm.

Weakly weathered fine tuff Weakly weathered fine tuff

1 2

10.67 6.28-7.94 (Avg. 7.11)

N: number of specimens; qu: uniaxial compressive strength; Avg.: average.

Yasukuni landslide area [10] and the Kanehana

landslide area [12] in northeastern Hokkaido, Japan.

Three ancient landslides are known to have

occurred in the Sattomonai-Okushunbetsu area in the

western part of Teshikaga Town [18]. Two in the

Sattomonai area and one in the northern part of the

Okushunbetsu area occurred within the hydrothermal

interstratified illite/smectite mineral zone and the

smectite zone, respectively [18]. These landslides are

classified as HAZLs based on their bedrock geology.

According to Ref. [18], the bedrocks of the landslide

in the northern part of the Okushunbetsu area are

weathered and hydrothermally altered rocks composed

mainly of fine tuff of the Upper Miocene Hanakushibe

Formation. This fine bedrock tuff belongs to a

smectite-bearing mordenite zone having a

hydrothermal alteration mineral assemblage of

mordenite-smectite-quartz whereas a debris of fine

tuff in the landslide body belongs to a

smectite-lacking mordenite zone having an

assemblage of mordenite-quartz. The landslide

occurred on a dip slope of fine tuff from the

Hanakushibe Formation. The scarp of the landslide

consists mainly of basaltic lava of Pekereyama Lava,

which is a cap rock. Therefore, the landslide is

classified as a weathered and hydrothermally altered

rockslide based on its landslide body [7, 30, 31] and

as an HAZL on the basis of bedrock geology. In

contrast, the bedrocks of the two landslides in the

Sattomonai area, according to Ref. [18], are also

weathered and hydrothermally altered rocks and are

mainly composed of lapilli tuff of the Upper Miocene

Oteshikaushinai Formation and Lower Pliocene

Ikurushibeyama Lava. Debris of lapilli tuff in the

landslide body belongs to the interstratified

illite/smectite mineral zone having a hydrothermal

alteration mineral assemblage of quartz-interstratified

illite/smectite minerals-calcite. The scarps of these

landslides consist mainly of andesitic lava from the

Ikurushibeyama Lava, which is a cap rock. Therefore,

the landslides are classified as weathered and

hydrothermally altered rockslides based on their

landslide body and as HAZLs based on their bedrock

geology.

In the Sattomonai-Okushunbetsu area, five ancient

landslides, including the OHS and the SHS occurred

within the hydrothermal smectite, interstratified

illite/smectite mineral, smectite-bearing mordenite,

and smectite-bearing laumontite zones. All these

landslides are classified as HAZLs on the basis of

their bedrock geology, and weathered and

hydrothermally altered rockslides on the basis of their

landslide body types. All these landslides also

occurred within weathered and hydrothermally altered

soft rocks. This indicates that HAZLs occur within

weathered and hydrothermally altered, very weak, soft

rocks of the smectite zone, interstratified

illite/smectite mineral zone, and smectite-bearing

zeolite zone such as the smectite-bearing mordenite

zone, smectite-bearing laumontite zone, etc.. The

HAZL potential within a hydrothermal area can,

therefore, be assessed by the swelling clay


326

mineral-bearing hydrothermal alteration types, dip

slope, and cap rock.

5. Conclusions

The relationship between two ancient landslides,

the OHS and SHS, and their geological characteristics

is as follows:

Both of the landslides occurred within the

Pliocene to Early Pleistocene hydrothermal alteration

zones in the tuffaceous clastic rocks and the

volcaniclastic rocks of the Upper Miocene

Hanakushibe and Shikerepe Formations. These

landslides are classified as HAZLs based on bedrock

geology;

Both of the landslides are classified as weathered

and hydrothermally altered rockslides based on their

landslide bodies.

The OHS occurred within the boundary area

between the hydrothermal smectite zone and

smectite-bearing mordenite zone.

The SHS occurred within the boundary area

between the hydrothermal smectite zone and

smectite-bearing laumontite zone.

The scarp of the OHS consists of a dike, whereas

that of the SHS consists of a cap rock of lava.

The HAZLs in the Sattomonai-Okushunbetsu area

of western Teshikaga Town, Hokkaido, Japan,

occurred within weathered and hydrothermally altered,

very weak, soft rocks such as those of the smectite,

interstratified illite/smectite mineral, smectite-bearing

mordenite, and smectite-bearing laumontite zones.

The HAZL potential within a hydrothermal field

can be assessed based on the swelling clay

mineral-bearing hydrothermal alteration types, dip

slope, and cap rock.

References

[1] H. Maeda, Hydrothermal alteration, in: Landslides: Topographic and Geological Recognition and Terminology, Committee of Topographic and Geological Terminology on Landslides, The Japan Landslide Society, 2004, pp. 159-164. (in Japanese)

[2] H. Maeda, Characteristics of topography, geology and alteration in slide areas: An example from the eastern region of the Ikutahara district in northeastern Hokkaido, Japan, J. of the Jpn. Landslide Soc. (Landslides) 33 (1996) 1-8. (in Japanese)

[3] H. Maeda, Ikutahara Slide, The Editorial Committee in the Hokkaido Branch of the Japan Landslide Society, The Hokkaido Branch of the Japan Landslide Society, 1999, pp. 86-90. (in Japanese)

[4] H. Maeda, Landslides and alteration zones (Part 1)―Relationship between landslides and hydrothermal alteration zones, Landslide Control Techniques 29 (2002) 29-37. (in Japanese)

[5] H. Maeda, T. Sasaki, K. Furuta, K. Takashima, A. Umemura, M. Kohno, What is a hydrothermal alteration zone landslide? The relationship between ancient landslides and point load strength of hydrothermal alteration zone rocks in Hokkaido, Japan, in: Proceedings of the First World Landslide Forum, Global Promotion Committee of the International Programme on Landslides (IPL), 2008, pp. 389-392.

[6] H. Koide, Landslides in Japan: Their Prediction and Countermeasures, Toyo Keizai Inc., 1955, p. 259. (in Japanese)

[7] A. Fujiwara, Landslide Investigations and Analyses, Riko-Tosho Press, 1970, p. 222. (in Japanese)

[8] T. Yamazaki, T. Kojima, T. Yamasaki, T. Kozai, Y. Yokota, Relation between landslides and alteration in Manza area, Gunma Prefecture, J. of the Jpn. Landslide Soc. (Landslides) 40 (2003) 68-77. (in Japanese)

[9] H. Maeda, H. Hiura, The Iwato Slide has characteristics of both shear zone slide and hydrothermal alteration zone slide, J. of the Jpn. Landslide Soc. (Landslides) 36 (1999) 24-31.

[10] H. Maeda, H. Hiura, The relationship between the Yasukuni Slide and hydrothermal interstratified illite/smectite minerals zone, J. of the Jpn. Landslide Soc. (Landslides) 37 (2001) 1-9.

[11] H. Maeda, S. Suzuki, H. Toshima, T. Yamada, Slides occurring in hydrothermal alteration zones: An example from the Kanehana slide area in the Rubeshibe district, northeastern Hokkaido, Japan, J. of the Jpn. Landslide Soc. (Landslides) 33 (1996) 19-24. (in Japanese with English abstract)

[12] H. Maeda, N. Oguchi, N. Matsumoto, Slide hazard mapping of Kanehana landslide area in Rubeshibe, northeastern Hokkaido, Japan, J. of the Jpn. Landslide Soc. (Landslides) 38 (2001) 61-68. (in Japanese with English abstract)

[13] M. Kohno, H. Maeda, Relationship between cylinder (longitudinal) point load strength and uniaxial compression strength for smectite-bearing fine tuffs in a


327

soft and semi-hard rock boundary area: Example of the Upper Miocene Ikutawara Formation from the Ikutahara-Minami landslide area, J. of the Jpn. Landslide Soc. (Landslides) 47 (2010) 17-25. (in Japanese with English abstract)

[14] S. Hasegawa, Y. Yoshida, W. Akagi, E. Tamura, D. Kanbara, Rock mass characterization for tunneling by the geological histry of hydrothermal alteration and landsliding, IAEG2006 Paper No. 580, Nottingham, 2006, pp. 1-13.

[15] E. Tamura, S. Hasegawa, H. Watanabe, K. Miyata, R. Yatabe, J. Uchida, Effect of hydrothermal alteration on landslides along the Median Tectonic Line, J. of the Jpn. Landslide Soc. (Landslides) 44 (2007) 222-232. (in Japanese with English abstract)

[16] Hokkaido Branch of the Japan Landslide Society, Landslides in Hokkaido, Hokkaido University Press, 1993, p. 392. (in Japanese)

[17] H. Yamagishi, M. Kawamura, Y. Ito, T. Hori, H. Fukuoka, Database of the Landslides in Hokkaido, Hokkaido University Press, Japan, 1996, p. 344. (in Japanese)

[18] H. Maeda, S. Sasaki, Slides occurring in hydrothermal alteration zones: Example from Sattomonai-Okushunbetsu slide area in Teshikaga district, Hokkaido, Japan, J. of the Jpn. Landslide Soc. (Landslides) 33 (1997) 20-25. (in Japanese with English abstract)

[19] H. Maeda, Y. Cai, Gold-silver mineralization in the Tobetsu ore deposit, eastern Hokkaido, Japan, IAGOD 1994 Abstracts, Vol. 2, 1994, pp. 789-790.

[20] H. Maeda, Y. Cai, K-Ar ages of epithermal gold-silver mineralizations from Akan-Taiho-Tobetsu mine area in Kitami metallogenic province, Hokkaido, Japan, Resource Geology 47 (1997) 247-253.

[21] J.B. Jones, E.R. Segnit, The nature of opal. 1. Nomenclature and constituent phases, Jour. Geol. Soc. Australia 18 (1971) 57-68.

[22] M. Minato, K. Yagi, M. Hunahashi, Geotectonic syntheses of the green tuff regions in Japan, Bull. Earthq. Res. Inst. Univ. Tokyo 34 (1956) 237-265.

[23] Report of Regional Geological Structure Survey: Northern Hokkaido B region, 1989 Fiscal Year, Ministry

of International Trade and Industry, Tokyo, 1990, p. 265. (in Japanese)

[24] Report of Regional Geological Struc- Ture Survey: Northern Hokkaido B Region, 1990 Fiscal Year, Ministry of International Trade and Industry, Tokyo, 1991, 505, p. (in Japanese)

[25] W. Hirose, M. Nakagawa, K-Ar ages of the Neogene volcanic rocks from the Kutcharo caldera region, east Hokkaido, with special reference to the Quaternary volcanic history, Jour. Geol. Soc. Japan 101 (1995) 99-102. (in Japanese)

[26] Report of Geothermal Energy Development Survey: Western Teshikaga District, No. 6 (Tokyo: New Energy and Industrial Technology Development Organization, 1985, p. 544. (in Japanese)

[27] T. Matsunami, M. Yahata, Geothermal resources of the Teshikaga area, east Hokkaido, Part 1―Conceptual model of geothermal system, Report of the Geological Survey of Hokkaido 60 (1989) 35-76. (in Japanese with English abstract)

[28] M. Yahata, H. Nishido, S. Okamura, K-Ar ages of Neogene volcanic rocks from the Abashiri-Akan district, eastern Hokkaido, Japan-with special reference to the formation of the Akan-Kutcharo Uplift Zone, Earth Science (Chikyu Kagaku) 49 (1995) 7-16. (in Japanese with English abstract)

[29] Y. Komine, M. Yahata, Pliocene hydrothermal activity in the Teshikaga district, south of Lake Kutcharo-ko, eastern Hokkaido, Japan, Report of the Geological Survey of Hokkaido 71 (2000) 1-12. (in Japanese with English abstract)

[30] M. Watari, A. Sakai, The point of view in rough survey and investigation on landslide area, Technical Memorandum of PWRI, No. 1003, 1975, p. 70. (in Japanese)

[31] H. Maeda, What should we do, from now on, to make progress on landslide science in the Hokkaido Branch of the Japan Landslide Society and the Hokkaido Landslide Society?, in: A 30-year Study on Landslides in Hokkaido,

Edited by the Hokkaido Landslide Society, The

Hokkaido Landslide Society and the Hokkaido, Branch of the Japan Landslide Society, Japan, 2008, pp. 1-10 (in Japanese).

Documents

1-Relationship between Landslides, Geologic Structures