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    Geology of the Hawaiian IslandsGeology of the Hawaiian IslandsClass 17Class 17

    9 March 20049 March 2004

    Any Questions?Any Questions?

    Mass WastingMass WastingLandslides, MudflowsLandslides, Mudflows

    Chapter 7Chapter 7

    Mass wastingMass wastingTransportation of large masses of Transportation of large masses of rockrockDownslopeDownslope movement of rock and movement of rock and soil debris under the influence of soil debris under the influence of gravitygravityVery important kind of erosion Very important kind of erosion

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    Mass wastingMass wastingGravity is the driving force of all Gravity is the driving force of all

    mass wastingmass wasting

    Mass wastingMass wasting

    Can range from smallCan range from small--scale scale processesprocesses

    soil creeping down slopesoil creeping down slopeTo much largerTo much larger--scale processesscale processes

    huge landslideshuge landslides

    Mass Wasting ProcessesMass Wasting Processes

    Talus

    TalusAccumu-lation of rock debris at the bottom of a slope

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    Angle ofRepose

    TalusFormed of loose rubble; Stands at the angle of repose (about 30-35)

    Angle of ReposeAngle of ReposeSteepest angle at which fragments will Steepest angle at which fragments will stand without further sliding or rolling stand without further sliding or rolling down hilldown hillControlled by:Controlled by:

    coarseness and size of fragmentscoarseness and size of fragmentsuniformity of size of the fragmentsuniformity of size of the fragments

    The larger and more uniform the size of The larger and more uniform the size of the fragments, the steeper the angle of the fragments, the steeper the angle of reposerepose

    Talus

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    LandslidesLandslidesOccur when a large piece of rock and/or Occur when a large piece of rock and/or soil breaks off and slides down hillsoil breaks off and slides down hillOften initiated by earthquakes and by very Often initiated by earthquakes and by very heavy rainstorms heavy rainstorms

    LandslidesLandslidesInitiated when rock/soil originally held in Initiated when rock/soil originally held in place by internal cohesion suddenly loses place by internal cohesion suddenly loses that cohesionthat cohesionForm on slopes that are steep enough for Form on slopes that are steep enough for the weight of the surficial material to the weight of the surficial material to overcome the cohesive force and fail overcome the cohesive force and fail

    Spoon-shapedsliding surface

    Steep HeadwallJumbled-upToes

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    LandslidesLandslidesTendency to slide increases with Tendency to slide increases with increasing surface slope increasing surface slope Addition of water promotes sliding by Addition of water promotes sliding by adding weight and by reducing cohesionadding weight and by reducing cohesionFriction along the slide surface controls Friction along the slide surface controls the speed of the the speed of the downslopedownslope movementmovement

    LandslidesLandslidesAddition of water reduces friction along Addition of water reduces friction along the surface and allows the mass to slide the surface and allows the mass to slide faster faster

    Some slides move as coherent massSome slides move as coherent mass

    Others break up and the material inside Others break up and the material inside becomes jumbled and disorganizedbecomes jumbled and disorganized

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    Blackhawk Landslide, Southern CaliforniaBlackhawk Landslide, Southern CaliforniaSlide moved 8 km down a slope of 2.5

    Slide is 100 m thick

    Moved on cushion of air;moved 8 km in about a minute = 400 km/hr (225 mph)

    Debris flowsDebris flowsOccur when the rock/soil mass loses Occur when the rock/soil mass loses coherency and lots of water is involvedcoherency and lots of water is involvedDebris becomes mixed up completely and Debris becomes mixed up completely and flows as liquid mudflows as liquid mudOften carry large Often carry large clastsclastsCan be very destructiveCan be very destructiveMore destructive in explosive volcanic More destructive in explosive volcanic terranes where ash blankets the slopes terranes where ash blankets the slopes and then becomes unstableand then becomes unstable

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    Soil CreepSoil Creep

    Mass movement that moves very Mass movement that moves very slowlyslowlyWeak soils on steep slopes move Weak soils on steep slopes move slowly down hillslowly down hill

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    Mass movement in dry regionsMass movement in dry regionsExample: leeward sides of the islandsExample: leeward sides of the islandsMost important processes: Most important processes:

    Gravity fallGravity fallSliding of rock fragmentsSliding of rock fragmentsDownDown--slope creep of soilslope creep of soil

    Mass movement in dry regionsMass movement in dry regionsChemical weathering less effectiveChemical weathering less effective

    Less soilLess soilFragmented rocks not badly Fragmented rocks not badly decomposeddecomposed

    Infrequent large rain storms erode large Infrequent large rain storms erode large amounts of material in a day or twoamounts of material in a day or twoLandslides are not very commonLandslides are not very common

    Mass movement in dry regionsMass movement in dry regionsWeathered rock held together by plant Weathered rock held together by plant rootsrootsDominated by soil avalanchesDominated by soil avalanchesSoil cover on steep slope pulls loose and Soil cover on steep slope pulls loose and slides downwardslides downward

    Mass movement in wet regionsMass movement in wet regions

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    Most slides small (less than 100 m long Most slides small (less than 100 m long downslopedownslope, less than 30m wide, and a few , less than 30m wide, and a few meters thick)meters thick)Occur most often after very heavy rainsOccur most often after very heavy rains

    Mass movement in wet regionsMass movement in wet regions LandslidesLandslidesCertain areas are more prone than Certain areas are more prone than othersothersUsually because of local geological Usually because of local geological factorsfactors

    If bedding dips down-slope, a landslide is more likely to develop

    LandslidesLandslidesCertain areas are more prone than Certain areas are more prone than othersothersUsually because of local geological Usually because of local geological factorsfactors

    Reducing vegetation that was Reducing vegetation that was stabilizing the soilstabilizing the soilOver watering (decrease friction)Over watering (decrease friction)

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    Cutting a slope during construction can cause a landslide

    OK to cutDangerousto cut

    LargeLarge--scale slumping and slidingscale slumping and slidingHas affected all of the islandsHas affected all of the islandsConfirming evidence has been Confirming evidence has been discovered in the past 10 years discovered in the past 10 years Major landslides have removed very Major landslides have removed very large pieces of the volcanoeslarge pieces of the volcanoes

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    Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Hawaiian Ridge

    Rotational slumps (nonRotational slumps (non--disintegrative) disintegrative) Debris avalanches (disintegrative)Debris avalanches (disintegrative)

    Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Hawaiian Ridge

    Rotational slumps Rotational slumps Broad (up to 110 km)Broad (up to 110 km)Short (30Short (30--35 km long35 km longThick (about 10 km)Thick (about 10 km)SteepSteep

    Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Hawaiian Ridge

    Debris avalanchesDebris avalanchesNarrow (a few 10s of km wide)Narrow (a few 10s of km wide)Long (up to 250 km)Long (up to 250 km)Happened quickly in one eventHappened quickly in one event

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    Landslides adjacent to the Landslides adjacent to the Hawaiian RidgeHawaiian Ridge

    Slumps occur during the major shield Slumps occur during the major shield building stagebuilding stageOnce volcanism stops, the islands are Once volcanism stops, the islands are probably stableprobably stable

    Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Caused by:Hawaiian Ridge Caused by:

    Steep slopes Steep slopes Young slopes of volcanoes very Young slopes of volcanoes very steepsteepBecome even steeper when the Become even steeper when the flanks of the volcanoes are inflated flanks of the volcanoes are inflated by volcanic activity by volcanic activity

    Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Caused by:Hawaiian Ridge Caused by:

    Volcanic activityVolcanic activityEarthquakesEarthquakes

    Shake the ground and cause failureShake the ground and cause failure

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    Tuscaloosa

    MolokaiOahu

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    TuscaloosaSeamount

    2.5 km Thick16 km Wide28 km Long

    Ko'olauVolcano Moved 90 km

    1,120 km3

    Caldera

    KilaueaKilaueaButtressed on north by Mauna LoaButtressed on north by Mauna LoaSouth flank is free surfaceSouth flank is free surface

    Hilina SlumpHilina Slump

    Off south flank of KilaueaOff south flank of KilaueaAbout 5200 kmAbout 5200 km22 in areain areaAbout 100 km wideAbout 100 km wideHeadwall is SWRZ of Kilauea on NW; Headwall is SWRZ of Kilauea on NW; Kilauea ERZ on the eastKilauea ERZ on the east

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    GPS MeasurementsReference

    1975 Kalapana Earthquake

    Magnitude 7.2 Magnitude 7.2 3 m of vertical 3 m of vertical movementmovement8 m of 8 m of horizontal horizontal displacementdisplacement

    Questions? Questions?

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    ThursdayThursdayField trip to Manoa LandslideField trip to Manoa LandslideMeet at Faculty Housing across from Manoa Meet at Faculty Housing across from Manoa Market PlaceMarket PlaceIf you are taking GG 101 Lab you dont need to If you are taking GG 101 Lab you dont need to go on this tripgo on this tripTake Rainbow Shuttle BEFORE 8:45 amTake Rainbow Shuttle BEFORE 8:45 amThere WILL be questions on Exam 2 about this There WILL be questions on Exam 2 about this triptrip

    Next Tuesday Next Tuesday

    Local Landslide HazardsLocal Landslide HazardsNext Thursday Next Thursday

    Exam 2Exam 2

    Will cover everything since Exam 1Will cover everything since Exam 1

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    Questions?Questions?