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Erosion

Erosion. GEOLOGY TODAY - Chapter 7 Barbara W. Murck Brian J. Skinner. HILLSIDE CREEP. N. Lindsley-Griffin, 1999. Erosion by Water. Erosion begins as soon as rain hits the surface and begins to run downhill. N. Lindsley-Griffin, 1999. Erosion by Water.

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Erosion

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  1. Erosion GEOLOGY TODAY - Chapter 7 Barbara W. Murck Brian J. Skinner HILLSIDECREEP N. Lindsley-Griffin, 1999

  2. Erosion by Water Erosion begins as soon as rain hits the surface and begins to run downhill. N. Lindsley-Griffin, 1999

  3. Erosion by Water 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) N. Lindsley-Griffin, 1999

  4. Erosion by Water Fine sediment carried in suspension gives the Huang He River of China its yellow color Fig. 7.20, p. 207 N. Lindsley-Griffin, 2000

  5. Erosion by Wind Wind can move only very small particles: sand by saltation, dust by suspension. (Fig. 7.21, p. 208) N. Lindsley-Griffin, 1999

  6. Erosion by Ice 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 N. Lindsley-Griffin, 1999

  7. Erosion by Ice 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) N. Lindsley-Griffin, 1999

  8. Erosion by Mass Wasting Rock fragments loosened by weathering move downhill under the pull of gravity. Angle of repose: Maximum angle at which loose material remains stable Talus Crater Lake N. P., OR N. Lindsley-Griffin, 1999

  9. Characteristics of landslide deposits Angular fragments Poorly sorted Locally derived No layering N. Lindsley-Griffin

  10. Balance of Forces on a Slope Slopes are stable if driving force (DF) of slope material is equal to, or less than, the resisting force (RF) CAUSES OF INSTABILITY: Adding weight Reducing friction Increasing slope Slope stable: DF   RF Slope unstable: DF  = RF N. Lindsley-Griffin, 1999

  11. Slope Failures: Slumps Shear strength: In solid rock depends on atomic forces In loose material depends on friction between material particles Fairly coherent blocks slip down on curved planes Blocks rotate backwards at top. May have mudflow at base. (Tab. 7.2, p. 210) N. Lindsley-Griffin, 1999

  12. Slumps: Turnagain Heights, AK 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 N. Lindsley-Griffin, 1999

  13. Slope Failures: Rockfalls Sudden and rapid Very steep slopes Consist of loose rock Not water-saturated (Tab. 7.2, p. 210) N. Lindsley-Griffin, 1999

  14. Slope Failures: Talus Small fragments accumulate at base of cliff Forms talus apron or talus slope Canadian Rockies N. Lindsley-Griffin, 1999

  15. Slope Failures: Debris Fall Debris is a mixture of rock, soil, trees, rock climbers….. (Tab. 7.2, p. 210) N. Lindsley-Griffin, 1999

  16. Slope Failures: Rockslide Rocks slide down a steep inclined plane (Tab. 7.2, p. 210) N. Lindsley-Griffin, 1999

  17. Slope Failures: Debris Slides A mixture of soil, regolith, rock, and other debris sliding on inclined planar surface (Tab. 7.2, p. 210) N. Lindsley-Griffin, 1999

  18. Sediment Flows: may be wet or dry 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) N. Lindsley-Griffin, 1999

  19. Wet Sediment Flows: Debris Flows Water-saturated slurry flow with particles larger than sand, moves rapidly (Tab. 7.2, p. 211) N. Lindsley-Griffin, 1999

  20. Wet Sediment Flows: Mudflows Rapid slurry flows consisting mostly of fine particles Lahars - hot volcanic mudflows (Tab. 7.2, p. 211) Lahar, 1985, Nevada del Ruiz, Colombia Buried 25,000 people, 15 meters thick, traveled 70 km/hour N. Lindsley-Griffin, 1999

  21. Dry Sediment Flows: Creep Imperceptible, slow, downslope movement of regolith (Tab. 7.2, p. 211) N. Lindsley-Griffin, 1999

  22. Dry Sediment Flows: Earthflows Relatively rapid granular flow of soil and regolith that is not water-saturated. (Tab. 7.2, p. 211) N. Lindsley-Griffin, 1999

  23. Dry Sediment Flows: Debris Avalanches Very rapid movement of rock and regolith. Rare, but extremely dangerous - several hundred mph. (Tab. 7.2, p. 211) N. Lindsley-Griffin, 1999

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