1Mass WastingEarth Science, Tarbuck and LutgensChapter 4, Pages 102-112Mass Wasting The downslope movement of rock, regolith, and soil under the direct influence of gravity Gravity 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 materials • Oversteepened slopes are unstable Important triggering factorsOversteepened slopes • Undercutting by streams• Undercutting by human interference• Addition of material to top of slope• Natural—deposition• Human-caused--construction2Important triggering factors• Removal of anchoring vegetation• Wildfires• Drought• Development, logging • Ground vibrations • from earthquakes Mass Wasting Types of mass wasting processes Defined by • The material involved • The movement of the material Types of mass wasting processesDefined by the material involved • Debris•Mud•Earth•RockTypes of mass wasting processesDefined by the movement of the materialThe character of the movement •Fall• Slide•FlowTypes of mass wasting processesDefined by the movement of the material The rate of the movement •Fast•SlowForms of mass wasting •Slump• Rockslide• Debris flow• Earth flow• Creep• Solifluction3Types of mass wastingUSGS Landslide Types• http://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.htmlForms of mass wastingSlump• Rapid movement along a curved surface• Occur along oversteepened slopes Slump—diagram Slump• http://www.physicalgeography.net/fundamentals/10x.htmlGovernment Hill, AK• 1964• http://walrus.wr.usgs.gov/geotech/radaraapg/fig4.html4Government Hill, AK seismic cross section• http://walrus.wr.usgs.gov/geotech/radaraapg/fig5.htmlForms of mass wastingRockslide • Rapid • Blocks of bedrock move down a slopeCousin to RockfallRockslide—diagramNevadoHuascarán• Peru 1970• Buried two towns• 18,000 killed• Geologists warned government of potentialhttp://landslides.usgs.gov/html_files/landslides/slides/slide5.htmGros Ventre rockslide--diagramGros Ventrelandslide—photo• http://www.goldengatephoto.com/WestUS/wyother.html#grosventre5Slide Lake, Wyoming• http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/GrosVentre.HTMSherman Glacier Rock Avalanche, March 1964 Rock 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 materials6Snohomish County, WAJanuary 2006• http://www.komotv.com/stories/41527.htmUS 50, Sierra Nevadas, California1997http://landslides.usgs.gov/monitoring/hwy50/index.phpLa Conchita, California• Spring 1995• No one injured or killed• http://landslides.usgs.gov/html_files/landslides/slides/slide21.htmLa Conchita, California• February 2005La Conchita, 2005• http://www.redcross.org/article/0,1072,0_312_3943,00.htmlSlide Mountain, Nevada, 1983http://landslides.usgs.gov/html_files/landslides/slides/slide2.htm1Debris flow damage 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.html2Armero site, Nevado del Ruiz• http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlPhilippine 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 regions • 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.html8Niigata, Japan, 1964• http://www.ce.washington.edu/~liquefaction/selectpiclique/nigata64/tiltedbuilding.jpgAnchorage, AK1964• http://www.owlnet.rice.edu/~sehh/AlaskaEQ/Alaska_Sci/EQScience• http://walrus.wr.usgs.gov/geotech/radaraapg/fig5.htmlAlaska, 1964• http://www.ce.washington.edu/~liquefaction/selectpiclique/alaska64/landslideintowater.jpgSheffield Dam, 1925Santa Barbara CountyEarth-quake caused flow• http://www.ce.washington.edu/~liquefaction/selectpiclique/dams/sheffielddam1.jpgLocation of Sarno, Italy9Forms of mass wastingCreep • Slow movement of soil and regolith downhill • Causes fences and utility poles to tilt Some visible effects of creepCreep• Bedrock curled due to creep mass wasting• http://www.ngdc.noaa.gov/seg/hazard/slideset/6/6_140_slide.shtmlCreep• Curved trunks due to soil 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 below10Solifluction Lobes• http://piru.alexandria.ucsb.edu/collections/geography3b/misc/solifluction_lobes_jpg%5b1%5d.jpgGround subsidence in Alaska due to solifluctionMeasuring ground movementMass 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 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 Mass Wasting The downslope movement of rock, regolith, and soil under
View Full Document
Unlocking...