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Mass Movement
Mass movement includes processes that transport large quantities of
rock, sediment, soil, etc. down a slope due to gravity. It occurs on
most slopes and can range from very slow to very fast
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Recent examples:
Hwy 410 in Washington State buried
http://seattletimes.nwsource.com/html/localnews/2010044629_webmudslide11m.
html
Topics:
19 Killed in Brazil
http://www.cbsnews.com/stories/2010/01/01/world/main6045455.shtml
Types of mass movement
Factors that affect the likelihood of mass movement
Triggering events
USGS list of major landslides by year
http://landslides.usgs.gov/recent/?PHPSESSID=n2jadq60bmt2hsv3kiji5l4ku6
What people can do about it
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Ophir Chasma
landslide, Mars
NASA
1995 landslide in La Conchita,
California Photos from U.S. Geological Survey
Next: landslide video
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Types of Mass movement
Gradual mass movement
Creep
Rapid mass movement
Landslides - any large, fast mass movement
Sub-Categories:
Fall
Slide
Flow
One type of mass movement can trigger or change into another as it moves downhill.
For example, an avalanche may sometimes produce mudflows.
Creep is the slowest type of mass
movement. Almost all slopes consisting
of unconsolidated material creep a few
millimeters up to several centimeters
per year. Creep may produce tilting of
objects such as fence posts, telephone
poles, and retaining walls. It also causes
curved trunks in trees on creeping
slopes. Fig 11.11 Understanding Earth and NOAA
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Fig 11.8 Understanding
Earth
Rockfall is the fastest type of mass
movement. It occurs when loose
material falls from very steep or
vertical slopes.
Small rockfall in a road cut in the Blue
Mountains of Oregon S. Kuehn
Types of rapid
mass movement
Another example - boulder on road:
Geology - Chernicoff
Fig 11.16 Understanding Earth
http://www.oes.ca.gov/Operational/OESHome.nsf/ALL/EF8986565A9A84FF88256F89006774D4?OpenDocument
Upper part of a slump
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Fig 11.13 Understanding Earth
Geology - Chernicoff
Fig 11.14 Understanding Earth
Fig 11.13 Understanding Earth
Slump - a type of slide that
separates along a concave
surface. Slumps generally do
not travel far, and the
material within the slump
tends to move as a unit and
not become mixed.
Debris flow or Mud
flow
- composed of rock
debris and mud;
includes a lot of water
Slump along a road
http://pubs.usgs.gov/mf/1999/mf-2325/
Debris flow deposits are often poorly sorted and may contain
boulders that are larger than normal stream flow can transport.
Ancient debris flows can be identified from similar deposits.
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Mass Movement
Some factors that influence or trigger mass movement:
• Type of slope material: sand, gravel, clay, bedrock, etc.
• How steep the slope is
• Amount of water
• Vegetation
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• Presence and orientation
of fractures or other zones
of weakness
http://pubs.usgs.gov/fs/2005/3106
Illustration: the maximum
stable slope angle (angle of
repose) for particles of
different sizes and shapes.
Fig 11.6 Understanding Earth
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Frequency of landslides and
amount of precipitation in the
Seattle area. The California
coast has a similar correlation
between rainfall and
landslides.
Figs 11.1, 11.3, 11.4 Understanding Earth
Fire can remove vegetation and decrease slope stability thereby
increasing the potential for erosion and mass movement
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Fractures along sedimentary16
bedding, Arizona
Enhanced erosion
following a fire
near San Luis Res.
Photo by S. Kuehn
Photo by S. Kuehn, October 2005
Fig 11.5 Understanding Earth
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Zones of weakness
such as fractures
and sedimentary
layers also
contribute to the
risk of mass
movement
Fractured volcanic rocks and
fallen boulders at Pinnacles
National Monument, CA
Cutting into slopes to build roads and
buildings increases the risk of mass
movement by making slopes steeper.
Photo by S. Kuehn
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Small landslide
(slump and
earthflow) in a
roadcut along
Hwy 70 in CA
The 1994
Northridge
earthquake in
California
triggered many
landslides
USGS OFR 95-213
Small rockfall in a road cut in
the Blue Mountains of Oregon
1994 landslide near
McClures Pass, Colorado
USGS
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What people can do about
mass movement
Avoid building on or near
slopes that show evidence of a
large amount of creep
Fig 11.11 Understanding Earth and NOAA
Construction on steep
slopes can put people at
greater risk from landslides
Chapter 11 Understanding Earth
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Watch out for early signs of movement and for evidence of past
mass movement. USGS OFR 95-213
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Avoid steep bluffs with
unconsolidated sediments
January, 1997
USGS OFR 98-239
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Control water and
improve drainage
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Stabilize landslide-prone slopes
e.g. by build sufficiently strong retaining structures
Installing drain
systems to reduce the
amount of water in a
slope can reduce the
risk of landslides.
S. Kuehn, 2005
Shannon & Wilson, Inc.
Keller – Environmental Geology
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Make maps to show where the risk is greatest.
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More about landslides
USGS Landslide Hazards Program
http://landslides.usgs.gov/
Landslide info from VA Dept. of Mines, Minerals, and Energy
http://www.dmme.virginia.gov/DMR3/landslides.shtml
VA Natural hazards (business-oriented site)
hhttp://www.vaemergency.com/business/hazthreats/natural/geologic/index.cfm
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About landslides and reducing the risks – WA State Dept. of Ecology
http://www.ecy.wa.gov/programs/sea/landslides/prevent/prevent.html
Landslide info from Calif. Emergency Management Agency
http://hazardmitigation.calema.ca.gov/hazards/natural/landslide
Kelso, WA landslide: amazing photos, landslide video, etc.
http://www.nwgeoscience.com/kelso/ (Aldercrest is best)
see also: http://landslides.usgs.gov/learning/nationalmap/
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130-year history of landslides for La Conchita, California
http://www.geog.ucsb.edu/~jeff/projects/la_conchita/apcg2001_article/apcg2001_article.html
Southern California—Debris Flows in Wildfire Areas
http://pubs.usgs.gov/fs/2005/3106/
Landslide hazard photos - NOAA Natural Hazard Slide set
http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=7&t=101634&s=0&d=1
Debris-Flow
Debris
Flow Hazards in the United States - U.S. Geological Survey
http://pubs.usgs.gov/fs/fs-176-97/
General overview of landslides
http://wapi.isu.edu/EnvGeo/EG4_mass_wasting/landslide2.html
contains a computer-simulated landslide
http://walrus.wr.usgs.gov/elnino/landslides-sfbay/photos.html
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