Landslides

1
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

2
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

3
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 gt400 km/h. Some 25,000
to 45,000 people died in the town of Yungay and
neighbouring villages.
4
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.
5
Canada landslide fatalities by province (1840
- present)
Frank slide
6
Canada fatalities by source (1840 - present)
7
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

8
(No Transcript)
9
Rockfall hazards in montane areas

• Wadi Al-Ayn, Hadramawt Valley, Yemen

Rockfall Al-Dhafir, Yemen 50 people
killed (December, 2005)
10
Sacred Falls Park, Oahu1999 Rockfall8 deaths,
many injuries
11
Rockfall, Camp Curry,Yosemite N.P., 1999(1
death)
12
Camp Curry, Yosemite N.P.Release areas
rockfall zones
13
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.
Photos Natural Resources Canada and Canadian
Press
14
Canadas 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
15

• 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.

16
The Barrier source of Rubble Creekrock
avalanche
17
(No Transcript)
18
Slumps, slides, etc.factors reducing slope
strength
log
19
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.

20
Location of slides in southern Puget Sound,
December 24-26, 1996
21
Debris slides in unconsolidated glacial and
fluvio-glacial deposits,Puget Sound(Dec
1996)Triggered by record rainfalls in one week
22
Surficial geologySeattle area
(or earthquake liquefaction)
permeable
piping ?
impermeable
23
(No Transcript)
24
Characteristic of massive fine-textured deposits
25
Escarpments and landslide risk areas in the GVRD
Source Eisbacher and Clague, 1980
26
La Conchitaearthflow,California
27
Landslide videos

Slump after heavy rains (Japan)
http//www.youtube.com/watch?vpJF-RhL4TvE
La Conchita earthflow
http//www.youtube.com/watch?vW4KWxglDL3o
28
Flowslides rapid earthflows(e.g. in leda
clays) Québec, Norway
29
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
30
FlowslideSt.-Jean-Vianney, Qué., 1971(31
deaths, 40 houses destroyed)
31
Aerial photo of flowslide, Nicolet, Québec
(1955)The church (circled) was later demolished
32
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
33

• 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.
• gt1500 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.

34
Debris flows, northern Venezuelain Dec. 1999 (30
000 deaths)
Debris flow scars on hillsides
Sediment deposition on alluvial fans
Suspended sediment offshore
Triggered by 1200 mm of rainfall in one month,
including 500 mm in two days
35
Settlements in canyons and on alluvial fans along
narrow coastal strip
Caraballeda
Note debris flow scars and deposits in valleys
Note size of boulders and height of debris flow
damage
36
Debris flows in Alberta Creek, Lions Bay (1983)
37
Debris flow in North Vancouver, Dec. 2005

• 1 death
• North Van. District purchased properties at risk
  installed piezometers to monitor water-table
  fluctuations.

38
Cheekye fan and its vicinity
39

• 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
  1930s. Flow volumes were 100 000 cubic metres.

40
Stump Lake cores
From Clague et al., 2003. Environmental and
Engineering Geoscience 9, 99-115.
41
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

42
Landslides, Sichuan earthquake May 2008
after (2008) before (2006)
Images NASA Earth Observatory
43
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 NASA Earth Observatory
44
Landslide dam failures
The 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.

landslide
scar lake outlet
Sketch of Lago Cari Lauquen on the Río Barrancas,
Argentina after the dam was breached(Groeber,
1916)
45
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.)

46
Protection/mitigation(rockfall shed on highway,
Taiwan)
47
Protection/mitigationhybrid hard-soft
landscaping solutions
Source Baumann Engineering (Laguna Beach CA,
project)
unplanted
mesh planting
48
Monitoring of high-risk landslidesEextensiomete
rsB instrumentedboreholes
Woodway
landslides.usgs.gov/woodway/ (no longer
continuously monitored)
49
Woodway
Daily precipitation (green) and water table
fluctuations Extensiometersmeasure creep
downslope (units cm)
Equipment malfunctionat E-1
50
Prevention/mitigation(trench drainage of toe of
active slide, Scotland)
51
Mitigation(debris torrent chute in Alps)
52
Debris flow dam Lions Bay
53
La Conchita II, Ventura Co. CA (Jan. 10,
2005)
Trigger 10 cmof rain in 24h
4 dead27 buried
54
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?