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Transcript of Mass Wasting - Western Oregon Universitybrownk/ES105/ES105.2006.0307.MassWasting.f.pdf · The...
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Mass Wasting
Earth Science, Tarbuck and LutgensChapter 4, Pages 102-112
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Mass Wasting
The downslope movement of rock, regolith, and soil under the direct influence of gravity
Gravity is the controlling force
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Mass Wasting
Important triggering factors• Saturation• Oversteepening• Removal of vegetation • Ground vibrations
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Important triggering factors
Saturation of the material with water• Destroys particle cohesion• Water adds weight
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Important triggering factorsOversteepened slopes
• Unconsolidated granular particles assume a stable slope called the angle of repose
• Stable slope angle is different for various materials
• Oversteepened slopes are unstable
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Important triggering factorsOversteepened slopes
• Undercutting by streams• Undercutting by human interference• Addition of material to top of slope
• Natural—deposition• Human-caused--construction
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Important triggering factors
• Removal of anchoring vegetation• Wildfires• Drought• Development, logging
• Ground vibrations • from earthquakes
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Mass Wasting Types of mass wasting processes
Defined by • The material involved • The movement of the material
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Types of mass wasting processes
Defined by the material involved • Debris• Mud• Earth• Rock
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Types of mass wasting processes
Defined by the movement of the materialThe character of the movement • Fall• Slide• Flow
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Types of mass wasting processes
Defined by the movement of the material The rate of the movement • Fast• Slow
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Forms of mass wasting • Slump• Rockslide• Debris flow• Earth flow• Creep• Solifluction
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Types of mass wasting
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USGS Landslide Types
• http://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html
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Forms of mass wastingSlump• Rapid movement along a curved surface• Occur along oversteepened slopes
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Slump—diagram
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Slump
• http://www.physicalgeography.net/fundamentals/10x.html
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Government Hill, AK
• 1964
• http://walrus.wr.usgs.gov/geotech/radaraapg/fig4.html
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Government Hill, AK seismic cross
section
• http://walrus.wr.usgs.gov/geotech/radaraapg/fig5.html
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Forms of mass wasting
Rockslide • Rapid • Blocks of bedrock move down a slope
Cousin to Rockfall
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Rockslide—diagram
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NevadoHuascarán
• Peru 1970
• Buried two towns
• 18,000 killed
• Geologists warned government of potential
http://landslides.usgs.gov/html_files/landslides/slides/slide5.htm
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Gros Ventre rockslide--diagram
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Gros Ventrelandslide—photo
• http://www.goldengatephoto.com/WestUS/wyother.html#grosventre
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Slide Lake, Wyoming
• http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/GrosVentre.HTM
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Sherman Glacier Rock Avalanche, March 1964
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Rock Fall
• July 1996• Yosemite
• http://landslides.usgs.gov/html_files/landslides/slides/slide9.htm
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Rock Fall
• http://sts.gsc.nrcan.gc.ca/geoscape/vancouver/graphics/mountain1.gif
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Forms of mass wastingDebris flow (mudflow)
• Rapid flow of debris with water• Confined to channels • Dry areas with heavy rains • Lahar composed of volcanic materials
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Snohomish County, WAJanuary 2006
• http://www.komotv.com/stories/41527.htm
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US 50, Sierra Nevadas, California
1997
http://landslides.usgs.gov/monitoring/hwy50/index.php
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La Conchita, California
• Spring 1995• No one injured or
killed
• http://landslides.usgs.gov/html_files/landslides/slides/slide21.htm
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La Conchita, California
• February 2005
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La Conchita, 2005
• http://www.redcross.org/article/0,1072,0_312_3943,00.html
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Slide Mountain, Nevada, 1983
http://landslides.usgs.gov/html_files/landslides/slides/slide2.htm
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Debris flow damage
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Lahar debris flow
• http://landslides.usgs.gov/html_files/landslides/slides/slide13.htm
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Toutle River Debris Flow
• http://pubs.usgs.gov/fs/fs-176-97/fs-176-97.html
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Forms of mass wastingEarthflow
• Rapid or slow• Typically occur on hillsides in humid
regions • Water saturates the soil • Liquefaction: associated with
earthquakes and clay soils
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Hollywood Hills, CA
• January 2005
• http://www.cnn.com/interactive/weather/0501/gallery.storms/frameset.exclude.html
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Niigata, Japan, 1964
• http://www.ce.washington.edu/~liquefaction/selectpiclique/nigata64/tiltedbuilding.jpg
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Anchorage, AK
1964
• http://www.owlnet.rice.edu/~sehh/AlaskaEQ/Alaska_Sci/EQScience
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• http://walrus.wr.usgs.gov/geotech/radaraapg/fig5.html
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Alaska, 1964
• http://www.ce.washington.edu/~liquefaction/selectpiclique/alaska64/landslideintowater.jpg
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Sheffield Dam, 1925
Santa Barbara County
Earth-quake caused flow
• http://www.ce.washington.edu/~liquefaction/selectpiclique/dams/sheffielddam1.jpg
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Location of Sarno, Italy
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Forms of mass wasting
Creep • Slow movement of soil and regolith
downhill • Causes fences and utility poles to tilt
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Some visible effects of creep
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Creep
• Bedrock curled due to creep mass wasting
• http://www.ngdc.noaa.gov/seg/hazard/slideset/6/6_140_slide.shtml
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Creep
• Curved trunks due to soil creep
• http://classes.colgate.edu/dkeller/geol101/massw/images/creep1.jpg
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Forms of mass wastingSolifluction
• Slow movement in areas underlain by permafrost
• Upper (active) soil layer becomes saturated and slowly flows over a frozen surface below
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Solifluction Lobes
• http://piru.alexandria.ucsb.edu/collections/geography3b/misc/solifluction_lobes_jpg%5b1%5d.jpg
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Ground subsidence in Alaska due to solifluction
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Measuring ground movement
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Mass Wasting Potential EXPLANATION
LANDSLIDE INCIDENCE
Low (less than 1.5% of area involved) Moderate (1.5%-15% of area involved)
High (greater than 15% of area involved)
LANDSLIDE SUSCEPTIBILITY/INCIDENCE Moderate susceptibility/low incidence High susceptibility/low incidence
High susceptibility/moderate incidence
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Mass Wasting Potential
EXPLANATION
LANDSLIDE INCIDENCE Low (less than 1.5% of area involved) Moderate (1.5%-15% of area involved)
High (greater than 15% of area involved)
LANDSLIDE SUSCEPTIBILITY/INCIDENCE Moderate susceptibility/low incidence High susceptibility/low incidence
High susceptibility/moderate incidence
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Mass Wasting The downslope movement of rock, regolith,
and soil under the direct influence of gravity
Gravity is the controlling forceImportant triggering factors
• Saturation of the material with water• Oversteepening• Devegetation• Vibration