1Mass WastingErosionChapter 23Mass Wasting The downslope movement of rock, regolith, and soil under the direct influence of gravity gyGravity is the controlling forceMass WastingImportant triggering factors• Saturation• Oversteepening• Removal of vegetation • Ground vibrationsImportant triggering factorsSaturation of the material with water• Destroys particle cohesion• Water adds weightImportant triggering factorsOversteepened slopes • Unconsolidated granular particles assume a stable slope called the angle of repose • Stable slope angle is different for various pgmaterials • Oversteepened slopes are unstable Important triggering factorsOversteepened slopes • Undercutting by streams• Undercutting by human interference•Addition of material to top of slopeAddition of material to top of slope• Natural—deposition• Human-caused--constructionImportant triggering factors• Removal of anchoring vegetation• Wildfires•DroughtDrought• Development, logging • Ground vibrations • from earthquakes Mass Wasting Types of mass wasting processes Defined by • The material involved •How the material moves•How the material movesTypes of mass wasting processesDefined by the material involved • Debris•Mud•Mud•Earth•Rock2Types of mass wasting processesDefined by how the material movesThe character of the movement •Fall•Fall • Slide •FlowTypes of mass wasting processesDefined by how the material movesThe rate of the movement •Fast•Fast•SlowForms of mass wasting •Slump• Rockslide• Debris flow•Earth flow•Earth flow• Creep• SolifluctionForms of mass wastingSlump• Rapid movement along a curved surface• Occur along oversteepened slopes Slump• http://www.physicalgeography.net/fundamentals/10x.htmlSlump—diagram •Scarp• Rotational blocksCk•http://geology.about.com/od/naturalhazardsclimate/ig/Landslides/slide-rotat.htm•Cracks • HummockytoeGovernment Hill, AK• 1964• http://walrus.wr.usgs.gov/geotech/radaraapg/fig4.htmlGovernment Hill, AK seismic cross section• http://walrus.wr.usgs.gov/geotech/radaraapg/fig5.htmlBlock slide at Vaiont Dam3Forms of mass wastingRockslide • Rapid • Blocks of bedrock move down a slopeCousin to Rockfall Rockslide—Howe Sound•http://www.flickr.com/photos/7605772@N08/2723218006•http://blog.fligtar.com/tag/travel/Elkton, Oregon, March 4, 2006• http://www.kmtr.com/news/local/story.aspx?content_id=010798AE-AF2F-41D5-93F5-120A64493D45Elkton, Oregon, March 4, 2006• http://www.kmtr.com/news/local/story.aspx?content_id=010798AE-AF2F-41D5-93F5-120A64493D45Nevado Huascarán• Peru 1970• Buried two ttowns• 18,000 killed• Geologists warned government of potentialhttp://landslides.usgs.gov/html_files/landslides/slides/slide5.htmGros Ventre rockslide--diagramGros Ventre landslide—photo• http://www.goldengatephoto.com/WestUS/wyother.html#grosventreSlide Lake, Wyoming• http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/GrosVentre.HTMSherman Glacier Rock Avalanche, March 19644Rock Fall• July 1996• Yosemite• http://landslides.usgs.gov/html_files/landslides/slides/slide9.htmRock Fall• http://sts.gsc.nrcan.gc.ca/geoscape/vancouver/graphics/mountain1.gifForms of mass wastingDebris flow (mudflow) • Rapid flow of debris with water• Confined to channels • Dry areas with heavy rains • Lahar composed of volcanic materialsDebris Flow•http://geology.about.com/od/naturalhazardsclimate/ig/Landslides/slide-debflow.htmSnohomish County, WAJanuary 2006• http://www.komotv.com/stories/41527.htmUS 50, Sierra Nevadas, California1997http://landslides.usgs.gov/monitoring/hwy50/index.phpDebris flow damageLa Conchita, California• Spring 1995• No one injured or jkilled• http://landslides.usgs.gov/html_files/landslides/slides/slide21.htmLa Conchita, California• February 20055Toes of La Conchita covering highway 101• http://www.cnn.com/interactive/weather/0501/gallery.storms/frameset.exclude.htmlLa Conchita, 2005• http://www.redcross.org/article/0,1072,0_312_3943,00.htmlSlide Mountain, Nevada, May 1983http://landslides.usgs.gov/html_files/landslides/slides/slide2.htm Lahar debris flow• http://landslides.usgs.gov/html_files/landslides/slides/slide13.htmToutle River Debris Flow• http://pubs.usgs.gov/fs/fs-176-97/fs-176-97.htmlNevado del Ruiz• http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlEruption of Nevado del Ruiz• http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlConfluence of lahars, Nevado del Ruiz• http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlArmero site, Nevado del Ruiz• http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.html6Philippine Landslide, 2006• http://www.alertnet.org/thenews/pictures/MAN52D.htmScar of Philippine landslide• http://news.yahoo.com/news?tmpl=story&u=/060219/481/xbm10202190643Forms of mass wastingEarthflow • Rapid or slow• Typically occur on hillsides in humid regionsregions • Water saturates the soil • Liquefaction: associated with earthquakes and clay soilsHollywood Hills, CA• January 2005• http://www.cnn.com/interactive/weather/0501/gallery.storms/frameset.exclude.htmlNiigata, Japan, 1964• http://www.ce.washington.edu/~liquefaction/selectpiclique/nigata64/tiltedbuilding.jpgAnchorage, AK1964• http://www.owlnet.rice.edu/~sehh/AlaskaEQ/Alaska_Sci/EQScience1964 liquefaction damage• http://walrus.wr.usgs.gov/geotech/radaraapg/fig5.htmlAlaska, 1964• http://www.ce.washington.edu/~liquefaction/selectpiclique/alaska64/landslideintowater.jpg• Hyperlink to sand boil liquefaction http://walrus.wr.usgs.gov/geotech/images/TIsandboils.movSheffield Dam, 1925Santa Barbara County, CAEthkEarth-quake caused earthflow• http://www.ce.washington.edu/~liquefaction/selectpiclique/dams/sheffielddam1.jpg7Forms of mass wastingCreep • Slow movement of soil and regolith downhill • Causes fences and utility poles to tilt Cause of creep—frost heaveSome visible effects of creepCreep• Bedrock curled due to creep mass wasting• http://www.gpc.edu/~janderso/physical/massw.htmCreep• Curved trunks due to soilsoil creep• http://classes.colgate.edu/dkeller/geol101/massw/images/creep1.jpgForms of mass wastingSolifluction• Slow movement in areas underlain by permafrost • Upper (active) soil layer becomes saturated and slowly flows over a frozen surface below Solifluction Lobes•
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