Erosion GEOLOGY TODAY - Chapter 7 Barbara W. Murck Brian J. Skinner HILLSIDE CREEP N....
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Transcript of Erosion GEOLOGY TODAY - Chapter 7 Barbara W. Murck Brian J. Skinner HILLSIDE CREEP N....
ErosionErosionGEOLOGY TODAY - Chapter 7
Barbara W. MurckBrian J. Skinner
HILLSIDE CREEP
N. Lindsley-Griffin, 1999
N. Lindsley-Griffin, 1999
Erosion by WaterErosion by Water
Erosion begins as soon as rain hits the surface and begins to run downhill.
Turbulent flow packs more energy than slower laminar flow.
Particles are carried as dissolved load, suspended load, bed load. (Fig. 7.19, p. 207)
(Fig. 7.18, p. 206)
Erosion by WaterErosion by Water
N. Lindsley-Griffin, 1999
Fine sediment carried in suspension gives the Huang He River of China its yellow color
Erosion by WaterErosion by Water
Fig. 7.20, p. 207
N. Lindsley-Griffin, 2000
Erosion by WindErosion by WindWind can move only very small particles: sand by saltation, dust by suspension. (Fig. 7.21, p. 208)
N. Lindsley-Griffin, 1999
Erosion by IceErosion by Ice
N. Lindsley-Griffin, 1999
Ice flows slowly downhill.
Density gives it laminar flow, ability to carry very large fragments. (Figs. 7.22A, C; p. 209)
Till, Matanuska Glacier, AK
Kaskawulsh Glacier, Yukon
Erosion by IceErosion by Ice
N. Lindsley-Griffin, 1999
Because of its density, ice has great power to erode and shape the landscape.
Polished and grooved surface made by Findelen Glacier, Swiss Alps.
(Fig. 7.22B, p. 209)
Erosion by Mass WastingErosion by Mass Wasting
N. Lindsley-Griffin, 1999
Rock fragments loosened by weathering move downhill under the pull of gravity.
Angle of repose:
Maximum angle at which loose material remains stable
TalusCrater Lake N. P., OR
Angular fragments
Poorly sorted
Locally derived
No layering
N. Lindsley-Griffin
Characteristics of landslide depositsCharacteristics of landslide deposits
Balance of Forces on a SlopeBalance of Forces on a Slope
N. Lindsley-Griffin, 1999
Slopes are stable ifdriving force (DF) of slope material is equal to, or less than, the resisting force (RF)
CAUSES OFINSTABILITY:Adding weightReducing frictionIncreasing slope
Slope stable: DF RFSlope unstable: DF = RF
Slope Failures: SlumpsSlope Failures: Slumps
N. Lindsley-Griffin, 1999
Fairly coherent blocks slip down on curved planes
Blocks rotate backwards at top.
May have mudflow at base.
Shear strength:In solid rock depends on atomic forces
In loose material depends on friction between material particles
(Tab. 7.2, p. 210)
Slumps: Turnagain Heights, AK
Slumps: Turnagain Heights, AK
N. Lindsley-Griffin, 1999
THE SETTING
City built on gravel layer
over a thick, water-soaked clay layer
THE TRIGGER
Anchorage, Alaska,
earthquake of 1964
THE RESULT
Liquefaction of clay layer
City slides towards the sea
Slope Failures: RockfallsSlope Failures: Rockfalls
N. Lindsley-Griffin, 1999
Sudden and rapid
Very steep slopes
Consist of loose rock
Not water-saturated
(Tab. 7.2, p. 210)
Slope Failures: TalusSlope Failures: Talus
N. Lindsley-Griffin, 1999
Small fragments accumulate at base of cliff Forms talus apron or talus slope
Canadian Rockies
Slope Failures: Debris FallSlope Failures: Debris Fall
N. Lindsley-Griffin, 1999
Debris is a mixture of rock, soil, trees, rock climbers…..
(Tab. 7.2, p. 210)
Slope Failures: RockslideSlope Failures: Rockslide
N. Lindsley-Griffin, 1999
Rocks slide down a steep inclined plane
(Tab. 7.2, p. 210)
Slope Failures: Debris SlidesSlope Failures: Debris Slides
N. Lindsley-Griffin, 1999
A mixture of soil, regolith, rock, and other debris sliding on inclined planar surface
(Tab. 7.2, p. 210)
N. Lindsley-Griffin, 1999
Slope stability and water:
Small amounts of water -
strengthen material
Large amounts of water -
increase weight
Material loses surface
tension
Sand liquefies
Clay swells
Solifluction - very slow movement of water-saturated slurry
(Tab. 7.2, p. 211)
Sediment Flows: may be wet or drySediment Flows: may be wet or dry
Wet Sediment Flows: Debris FlowsWet Sediment Flows: Debris Flows
N. Lindsley-Griffin, 1999
Water-saturated slurry flow with particles larger than sand, moves rapidly
(Tab. 7.2, p. 211)
Wet Sediment Flows: MudflowsWet Sediment Flows: Mudflows
N. Lindsley-Griffin, 1999
Lahar, 1985, Nevada del Ruiz, Colombia
Buried 25,000 people, 15 meters thick, traveled 70 km/hour
Rapid slurry flows consisting mostly of fine particles
Lahars - hot volcanic mudflows
(Tab. 7.2, p. 211)
N. Lindsley-Griffin, 1999
Imperceptible, slow, downslope movement of regolith
Dry Sediment Flows: CreepDry Sediment Flows: Creep
(Tab. 7.2, p. 211)
Dry Sediment Flows: EarthflowsDry Sediment Flows: Earthflows
N. Lindsley-Griffin, 1999
Relatively rapid granular flow of soil and regolith that is not water-saturated.
(Tab. 7.2, p. 211)