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Mass Wasting Wasting Chapter 12. Ch. 12 Mass wasting MASSWASTING 1.Landform development 2.Controls and triggers 3.Mass wasting processes 4.Rock slides

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Text of Mass Wasting Wasting Chapter 12. Ch. 12 Mass wasting MASSWASTING 1.Landform development 2.Controls...

  • Mass WastingChapter 12

  • Ch. 12 Mass wastingMASSWASTINGLandform developmentControls and triggersMass wasting processesRock slidesEarth creepEarth flowDebris and mud flowSlump and debris slides

  • 1) Landform developmentMASSWASTINGMass wasting downslope movement of rock, regolith, soil from force of gravity one form of erosion follows weathering mass-wasting + running water = stream valleysMass wasting and streams sculpt Earths surface

  • 2) Controls and triggersMASSWASTINGcontrolling force: gravityother important factors: water saturation

    over-steepened slopes

    vegetation removal

    earthquakesWater fills pore spaces between sediments,reduces internal resistance, adds weight Plants add slope stability byprotection against erosionStrong ground vibrationsToo steep = unstableangle of repose = steepest stable angle of a slope

  • Angle of repose: Steepest slope that can remain stable

    Sand has a small angle of repose, with increasing grain size and angularity the angle increases

    Moisture means larger angle of repose

    Talus slope, Wheeler Peak,Great basin Natl ParkFig. Story 12.1

  • Vector diagramAngle of dip

  • Downslope forceNormal forceIf down slope force < friction, rock stays putVector diagramFrictionAngle of dip

  • Downslope forceNormal forceIf we steepen slope, down slope force > friction, rock starts sliding. The angle where that happens is the angle of repose.Vector diagramAngle of dipFrictionMass movements occur when the force of gravity (meaning the downslope component) exceeds the strength (meaning frictional adhesion) of the slope materials.

  • 3) Mass wasting processesMASSWASTING

    Type of material

    Type of motion

    Rate of movementSoil/regolith -or- rock/bedrockFall - free-fall of materialSlide - coherent material slides along defined surfaceFlow - material flows as viscous fluidFastest - rock avalanche: floats (flows) on trapped airSlowest - creep: inches per year (or less)

  • 4) RockslideMASSWASTINGBlocks of bedrock break loose, slide down slope

    usually where strata are inclined

    causes:Base of slope is undercutRain or melting snow lubricates a sliding surface

  • 5) Earth creepMASSWASTING Creep

    Slow downhill movement of material.

    From alternate expansion/contraction of material fromfreezing/thawing or wetting/drying

  • 6) EarthflowMASSWASTING humid areas hillsides rich in clay/silt slow rates

  • 7) Debris and mud flowMASSWASTING

  • 8) Slump and debris slidesMASS WASTING downward sliding of material moves as a whole section on curved surface usually slow, material doesnt go far often involves multiple blocks commonly due to slope over-steepeningFig. 12.6

  • Some MC.MASSWASTINGWhich of the following statements is false?

    A. Mass movements occur when the force of gravity exceeds the strength of the slope materials.B. Mass movements can be triggered by earthquakes and floods.C. Materials can move down a slope very slowly or as a sudden, catastrophic, large movement.D. Mass movements require wind or running water.

  • Some MC.MASSWASTINGWhich of the following is not an important factor in causing mass movements?

    A. amount of water in materialsB. nature of slope materialsC. steepness and instability of slopesD. temperature of slope materials

  • Some MC.MASSWASTINGA hill consisting of loose, dry sand that slopes at the angle of repose and has no vegetation ______.

    A. is stable unless oversteepened by excavationB. may flow if it becomes saturated with waterC. will be more stable if vegetation takes root on the hillD. all of the above

  • Some MC.MASSWASTINGWhat is the difference between a rockslide and a rock avalanche?

    A. In a rockslide, the rocks move more or less as a unit, whereas in a rock avalanche the rocks move independently like a fluid.B. In a rockslide, the rocks move independently like a fluid, whereas in a rock avalanche the rocks move more or less as a unit.C. A rockslide is faster than a rock avalanche.D. A rockslide involves more debris than a rock avalanche.

  • Some MC.MASSWASTINGWhich of the following statements about mudflows is false?

    A. Mudflows tend to move slower than debris flows.B. Mudflows are most common in semi-arid regions.C. Mudflows contain large amounts of water.D. Mudflows can carry large boulders.

  • Some MC.MASSWASTINGTelephone poles that lean slightly downhill are a likely result of which of the following processes?

    A. creepB. debris slideC. earthflowD. rock avalanche

  • Some MC.MASSWASTINGA slump is __________.

    A. a rock flowB. a rock slideC. a flow of unconsolidated materialD. a slide of unconsolidated material