Landslides

Landslides

•FALLS - material falls through air•AVALANCHES - material in air or on surface •SLIDES or SLUMPS - material slides across surface•FLOWS - material flows across surface

Landslide and avalanche hazards

• Thousands of people killed annually world-wide

• Annual property damage ~$1.5 billion in USA, probably tens of billions world-wide

• Small to medium-sized events responsible for most of the property damage

Examples of landslide disasters

1970 - Yungay, Peru A minor earthquake loosened a small mass of glacial ice and rock on the flanks of Mt. Huascaran in the Peruvian Andes. It fell ~650 m and landed on a mass of unconsolidated rock. The resultant debris avalanche cascaded downvalley for a distance of 65 km, reaching speeds of >400 km/h. Some 25,000 to 45,000 people died in the town of Yungay and neighbouring villages.

Examples of

landslide disasters

1903 - Frank, AlbertaA rock avalanche (30 M m3) slid off the eastern face of Turtle Mountain, covering 3 km in about 100 seconds. The avalanche buried the outskirts of the mining town of Frank. Some 75 people died.Monitored since 1933.

Canada: landslide fatalities by province

(1840 - present)

NewfoundlandQuébecOntarioAlbertaBC

Frank slide

Canada: fatalities by source (1840 - present)

Snow av.Rock slide/av.Debris av.SlumpFlowslideDebris flowBreach of dam

Falls, slides, slumps and flows

•Slope angle - the steeper the gradient,

the more likely it is to fail

•Substrate - unconsolidated sediments and fractured rocks more prone to failure than massive or well-cemented rocks

•Water - the more saturated the material, the more likely it is to fail

Rockfall hazards in montane areas

Wadi Al-Ayn, Hadramawt Valley,

Yemen

Rockfall; Al-Dhafir, Yemen: ~50 people

killed(December, 2005)

Sacred Falls Park, Oahu1999 Rockfall

8 deaths, many injuries

Rockfall, Camp Curry,

Yosemite N.P., 1999

(1 death)

Camp Curry, Yosemite N.P.Release areas & rockfall zones

Rockfalls: BC

Fraser Canyon

This rockfall near Furry Creek in July 2008 covered 75 metres of the Sea to Sky Highway in rubble 10 metres deep and also took out the railway line below the highway. The highwaywas closed for 3 days. The slope was stabilized by blasting.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Photos: Natural Resources Canada and Canadian Press





Canada’s largest rock avalanche in the historic period (January, 1965)46 million cubic meters of rock debris avalanched down a the side of a mountain in SW BC in January 1965 forming a fan up to 80 m thick and 3 km wide, Four people driving on the Hope-Princeton Highway were killed. There is no known triggering event for this slide.

Photos: Natural Resources Canada



Rock/debris avalanches - Rubble Creek

Site of two large debris avalanches and several debris flow

during the Holocene.

Source of the landslides is The Barrier, which is a precipitous

rock face formed by a 300 m thick lava flow which abutted

against a glacier occupying Cheakamus valley in the late

glacial. Much of the landslide debris from this cliff has

formed a fan at the mouth of Rubble Creek.

The fan consists of 5 - 10 landslide units, each 5 - 10 m in

thickness. Total volume ~ 170 million cubic metres.

Most recent failure occurred in 1855-56. That avalanche (~

30 million cubic metres) traveled 6 km down Rubble Creek at

a speed of 60 m/s in the upper part of the path, and 25-40

m/s down-valley.

The Barrier : source of Rubble Creekrock

avalanche

Slumps, slides, etc.factors reducing slope strength

Frictio

nal strength

keeps materia

l on slope

rain load

quake

cut/erode

log

Earthquake-induced landslides

This shallow debris slide near Tacoma (WA) was initiated by the Olympia earthquake of 1949. The failure occurred several days after the earthquake. The landslide generated a small tsunami in the Narrows.

Location of slides in southern Puget Sound, December 24-26, 1996

Debris slides in unconsolidated

glacial and fluvio-glacial

deposits,Puget Sound

(Dec 1996)

Triggered by record rainfalls in one week

Surficial geology:Seattle area

permeable

impermeable

“piping” ?

(or earthquake liquefaction)

Characteristic of massive fine-textured deposits

Escarpments and landslide risk areas in the GVRD

Source: Eisbacher and Clague, 1980

La Conchitaearthflow,California

http://www.youtube.com/watch?v=W4KWxglDL3o

La Conchita earthflow

Slump after heavy rains (Japan)

http://www.youtube.com/watch?v=pJF-RhL4TvE

Landslide videos

http://www.youtube.com/watch?v=W4KWxglDL3o

http://www.youtube.com/watch?v=pJF-RhL4TvE

Flowslides= rapid

earthflows(e.g. in leda

clays)

Québec, Norway

Landslides in glaciomarine clays of the Champlain

Sea Extent of the

Champlain Sea (black dots =

whale fossils in GM deposits)

Slides predominantly along river banks

FlowslideSt.-Jean-Vianney,

Qué., 1971(31 deaths, 40 houses destroyed)

Aerial photo of flowslide, Nicolet, Québec (1955)

The church (circled) was

later demolished

Debris flows, Typhoon Durian, Philippines

(Dec. 2006)

Heavy rain from Typhoon Durian unleashed mudslides from the flanks of Mt. Mayon in the Phillipines, which had been active in July-August (top right). Photos: BBC News

Hurricane Stan (and other storms) dumped upwards of 500 mm of rain in southern Mexico - El Salvador in a 6-day period in October 2005. Debris flows and mudslides occurred in the highlands and floods in the valleys.

>1500 people died in Guatemala. Most of the deaths occurred in the small town of Panabaj, which was engulfed in a mudslide up to 12m thick. As in the Phillipines, the mudslides were derived from recent volcanic deposits.

Debris flows, northern Venezuela

in Dec. 1999 (30 000 deaths)

Triggered by 1200 mm of rainfall in one month, including 500 mm in two

days

3

2

1

1

2

3

Debris flow scars on hillsides

Sediment deposition on alluvial fans

Suspendedsedimentoffshore

Settlements in canyons and on

alluvial fans along narrow coastal strip

Note size of boulders and

height of debris flow damage

Caraballeda

Note debris flow scars and deposits in valleys

Debris flows in Alberta Creek, Lions Bay (1983)

Debris flow in North

Vancouver, Dec. 2005

• 1 death• North Van. District

purchased properties at risk; installed piezometers to monitor water-table fluctuations.

Cheekye fan and

its vicinity

Cheekye Fan Site of many large debris avalanches and several moderate

to large debris flows during the Holocene.

Source of the landslides is the west flank of the volcanic cone

of Mt. Garibaldi, which may have been partly built on top of

valley ice in the late glacial. This flank is therefore subject to

collapse. Much of the landslide debris from this cliff has

formed a fan at the mouth of the Cheekye River.

The fan consists of many landslide units, only some of which

have been adequately dated. Total volume ~ 2.5 - 3 billion

cubic metres.

• Debris flows have continued in historic times. In 1958 a debris

flow swept down the Cheekye River and formed a 5 m dam

across the Cheakamus at its mouth. A similar event occurred

in the 1930’s. Flow volumes were

~100 000 cubic metres.

Stu

mp

Lake

core

s

From: Clague et al., 2003. Environmental and Engineering Geoscience 9, 99-115.

Landslide dams

• Large landslides may form temporary dams across valleys; e.g. oral traditions describe Native Americans crossing the Columbia River on the “Bridge of the Gods” slide complex (product of AD1700 megaearthquake?)

• Landslide dams may fail catastrophically

Landslides, Sichuan earthquake: May 2008

after (2008) before (2006)

Images: NASA Earth Observatory

Lake formed by landslide dam, Sichuan, May

2008

At least 20 lakes were formed behind seismically-triggered

landslide dams in the area affected by the Sichuan

earthquake. The inhabitants of towns downstream of the

dams (e.g. Beichuan) were evacuated because of the risk

of debris flows and floods if the dams failed catastrophically.

Images:

NA

SA

Eart

h O

bse

rvato

ry

Landslide dam failuresThe Río Barrancas, in northwestern Argentina, was dammed in prehistoric time by a large landslide, forming a 21-km-long lake. In 1914, the Río Barrancas breached this dam; overnight the lake surface was lowered about 95 m. The resultant debris flow/flood had an estimated volume of 2 billion m3. No data are available on casualties or damage costs downstream, but cattle ranches and farms along the 60-km canyon and valley of the Río Barrancas completely disappeared. In addition, two small towns in the valley were devastated.

Sketch of Lago Cari Lauquen on the Río Barrancas, Argentina after the dam was breached(Groeber, 1916)

landslide scar

lake outlet

Preventive measures: rockfalls

• Rock bolts (tie loose rocks to stable base)• Shotcrete (debris adheres to stable base)• Guard mesh (captures rockfall material)• Drainage pipes (relieve pore pressure in basal rocks)• Rockfall sheds (deflect material over highways, etc.)

Protection/mitigation(rockfall shed on highway,

Taiwan)

Protection/mitigation:hybrid “hard-soft” landscaping

solutionsSource: Baumann Engineering (Laguna Beach CA, project)

mesh + planting

unplanted

Monitoring of high-

risk landslidesE=extensiometer

sB= instrumented

boreholesWoodway

landslides.usgs.gov/woodway/ (no longer continuously monitored)

Woodway

Daily precipitation (green) and water table fluctuations

Extensiometersmeasure creep downslope (units = cm)

Equipment malfunctionat E-1

Prevention/mitigation(trench drainage of toe of active slide,

Scotland)

Mitigation(debris torrent chute in Alps)

Debris flow dam: Lions Bay

La Conchita II, Ventura Co. [CA]: (Jan. 10, 2005)





4 dead27 buried

Trigger:10 cmof rain in 24h

La Conchita II: why?Mitigation: $400,000 retaining

wall (destroyed)

Preparedness: some recent

residents claimed to be unaware of the slide danger! Did anyone move from this subdivision to a safer location after1995?

Documents

Landslides