#13 Landslides
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Transcript of #13 Landslides
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Landslides
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Volcanoes&Earthquakesinvolvetheinternalfunctionsoftheplanet
Wewillnowdiscusserosiveprocessesandgravityandhowtheybringdownmaterialthathasbeenthrustupduetoplatetectonics
Landslidesaretheresultofalostbattlebetweentwoforces Drivingforce gravityworkingwiththeweightofthematerial(rock)tobringitdownward
Resistingforce frictionworkingtoholditup
GSC350NaturalDisasters
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AngleofRepose steepestangleatwhichloosematerialisstable
GSC350NaturalDisasters
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Manyfactorsleadtoslopefailure Yourbookgoesintoalotofdetail,butconsider
Slopeangle steepnessofaslope Load theweightofmaterialonthatslope Frictionalresistance dependantonthosetwo,areaofcontactofasurface
Whendownwardforceexceeds(isgreaterthan)frictionalresistance,slopefailureoccurs
MoreonthisandsomemathonThursday
GSC350NaturalDisasters
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Landslidetypeandtriggerrelyonthematerialthatissliding/falling Clays Claysretainandholdwater,andduetomolecularpropertiescananddobecomeslick Smectite atypeofclaythatadsorbswaterandduetoH20slackofsupportstrength,failseasily
QuickClays Saline(saltwater)claysthatareheldtogetherwithmolecularcharges.Oncedisturbed,theyfailcatastrophically,likeadeckofcards
GSC350NaturalDisasters
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Landslidetypeandtriggerrelyonthematerialthatissliding/falling Rockcanfaildependantonafewfeatures,considerfractureswithinarock.
Daylighting beds/fractures arefractures/bedsthatintersectacliff(roadcut)atasteepangleidealforfailure
GSC350NaturalDisasters
Notdaylighting
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GSC350NaturalDisasters
Daylighting fractureandbedsDaylighting beds
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GSC350NaturalDisasters
Landslidetypes(toknow) Rockfalls Arockbreaksawayfromasteepcliffandfalls
DebrisAvalanches Materialbreaksapartandintosmallpieces,flowingdownhill
Rotational(slumps) Softnonlinearmaterialslidesincurvingmotion
Translational Movementoccursonweakplanesandareparalleltoaslope
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GSC350NaturalDisasters
Rockfalls occurwhenmassesofrockbreakawayformaclifforslopeandplummetdownward. Aresultofgravity Occurduetofractureswithintherock Ice,water,stresses
Angleofrepose
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GSC350NaturalDisasters
Transferofpotentialenergytokineticenergy Rocksbounceorrolldependingonslope
Runout lengthdependsonslopeheight,andslopeangle()
Runout Length=height/Tan()
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GSC350NaturalDisasters
Runout Length=height/Tan()
Arockisfalling100ftontoaslopeof30,whatisitsrunout length?
100ft/(Tan(30))
173ft!
Whatifyourhouseis~100ftdownslopefromaboulder?
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GSC350NaturalDisasters
Similarinitiationasarockfall,butoftenmuchlarger,anditbreaksintosmallerpiecesandactsasafluidflow Takeinandtrapairwithintheflowandcanevenflowabovethegroundifelevated(hittingaridge)
Verydeadlyanddevastating Canthrowmaterialformilesiflargeenough
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GSC350NaturalDisasters
Alsoknownasslumps Rotationalnameisusedastheymovealongacircularpathandrotatearoundapoint
Headscarp Upperextentofslidewheregravityactsdownward
Toe Extentofslidereach SlidePlane Planeuponwhichmovementisoccurring
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GSC350NaturalDisasters
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GSC350NaturalDisasters
Similartorotationalbutoccuralongalinearplane(notacircularpath) Asaresult,theyreoftenfaster Occuralongrocksurfaces,soilhorizons,anyplaneofweakness(recallclays)
Notedifferencesbetweenrotational/translational
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GSC350NaturalDisasters
Rotationalslidespenetratedeepintotheground,translationaldonot
Bothhaveatoe andheadscarp Notenotonlydifferencesinmovement,butendresultsaswell
Figure824ofyourbook(pg.213) Listentothetrees
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GSC350NaturalDisasters
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GSC350NaturalDisasters
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GSC350NaturalDisasters
Considerwhatdisturbsthelandandcancreatealandslide
Earthquakescantriggerlandslides Createshakinganddislocationofpotentiallyunstablematerial Rockfalls Debrisavalanches Caninfluenceclaysduetowatermovementetc.
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GSC350NaturalDisasters
Landslidedams arecommon Materialslidesintoavalleyandcreatesanaturaldaminthepathofariver/creek
Duetothelargeamountofmaterialinlandslides,thedamsoftenlastforyears
Largeslidesoftenstable,smalleronescanfailcatastrophically
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GSC350NaturalDisasters
Moremovingearth!
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