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.

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 Water N. Lindsley-Griffin, 1999

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

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

Erosion 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 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 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 Talus Crater Lake N. P., OR

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

Balance of Forces on a Slope N. Lindsley-Griffin, 1999 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

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

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

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

Slope 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 dry

Wet 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: 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: Creep (Tab. 7.2, p. 211)

Dry 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)

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