#13 Landslides

21
Landslides

description

A powerpoint about landslides.

Transcript of #13 Landslides

  • Landslides

  • Volcanoes&Earthquakesinvolvetheinternalfunctionsoftheplanet

    Wewillnowdiscusserosiveprocessesandgravityandhowtheybringdownmaterialthathasbeenthrustupduetoplatetectonics

    Landslidesaretheresultofalostbattlebetweentwoforces Drivingforce gravityworkingwiththeweightofthematerial(rock)tobringitdownward

    Resistingforce frictionworkingtoholditup

    GSC350NaturalDisasters

  • AngleofRepose steepestangleatwhichloosematerialisstable

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  • Manyfactorsleadtoslopefailure Yourbookgoesintoalotofdetail,butconsider

    Slopeangle steepnessofaslope Load theweightofmaterialonthatslope Frictionalresistance dependantonthosetwo,areaofcontactofasurface

    Whendownwardforceexceeds(isgreaterthan)frictionalresistance,slopefailureoccurs

    MoreonthisandsomemathonThursday

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  • Landslidetypeandtriggerrelyonthematerialthatissliding/falling Clays Claysretainandholdwater,andduetomolecularpropertiescananddobecomeslick Smectite atypeofclaythatadsorbswaterandduetoH20slackofsupportstrength,failseasily

    QuickClays Saline(saltwater)claysthatareheldtogetherwithmolecularcharges.Oncedisturbed,theyfailcatastrophically,likeadeckofcards

    GSC350NaturalDisasters

  • Landslidetypeandtriggerrelyonthematerialthatissliding/falling Rockcanfaildependantonafewfeatures,considerfractureswithinarock.

    Daylighting beds/fractures arefractures/bedsthatintersectacliff(roadcut)atasteepangleidealforfailure

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    Notdaylighting

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    Daylighting fractureandbedsDaylighting beds

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    Landslidetypes(toknow) Rockfalls Arockbreaksawayfromasteepcliffandfalls

    DebrisAvalanches Materialbreaksapartandintosmallpieces,flowingdownhill

    Rotational(slumps) Softnonlinearmaterialslidesincurvingmotion

    Translational Movementoccursonweakplanesandareparalleltoaslope

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    Rockfalls occurwhenmassesofrockbreakawayformaclifforslopeandplummetdownward. Aresultofgravity Occurduetofractureswithintherock Ice,water,stresses

    Angleofrepose

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    Transferofpotentialenergytokineticenergy Rocksbounceorrolldependingonslope

    Runout lengthdependsonslopeheight,andslopeangle()

    Runout Length=height/Tan()

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    Runout Length=height/Tan()

    Arockisfalling100ftontoaslopeof30,whatisitsrunout length?

    100ft/(Tan(30))

    173ft!

    Whatifyourhouseis~100ftdownslopefromaboulder?

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    Similarinitiationasarockfall,butoftenmuchlarger,anditbreaksintosmallerpiecesandactsasafluidflow Takeinandtrapairwithintheflowandcanevenflowabovethegroundifelevated(hittingaridge)

    Verydeadlyanddevastating Canthrowmaterialformilesiflargeenough

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    Alsoknownasslumps Rotationalnameisusedastheymovealongacircularpathandrotatearoundapoint

    Headscarp Upperextentofslidewheregravityactsdownward

    Toe Extentofslidereach SlidePlane Planeuponwhichmovementisoccurring

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    Similartorotationalbutoccuralongalinearplane(notacircularpath) Asaresult,theyreoftenfaster Occuralongrocksurfaces,soilhorizons,anyplaneofweakness(recallclays)

    Notedifferencesbetweenrotational/translational

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    Rotationalslidespenetratedeepintotheground,translationaldonot

    Bothhaveatoe andheadscarp Notenotonlydifferencesinmovement,butendresultsaswell

    Figure824ofyourbook(pg.213) Listentothetrees

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    Considerwhatdisturbsthelandandcancreatealandslide

    Earthquakescantriggerlandslides Createshakinganddislocationofpotentiallyunstablematerial Rockfalls Debrisavalanches Caninfluenceclaysduetowatermovementetc.

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    Landslidedams arecommon Materialslidesintoavalleyandcreatesanaturaldaminthepathofariver/creek

    Duetothelargeamountofmaterialinlandslides,thedamsoftenlastforyears

    Largeslidesoftenstable,smalleronescanfailcatastrophically

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    Moremovingearth!

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