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Mass wasting. 11:37 am on August 17, 1959 magnitude 7.1? earthquake West Yellowstone, Montana triggered landslide of 85 million tons of rock sped downslope.

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Presentation on theme: "Mass wasting. 11:37 am on August 17, 1959 magnitude 7.1? earthquake West Yellowstone, Montana triggered landslide of 85 million tons of rock sped downslope."— Presentation transcript:

1 mass wasting

2 11:37 am on August 17, 1959 magnitude 7.1? earthquake West Yellowstone, Montana triggered landslide of 85 million tons of rock sped downslope at 150 km/hr and produced hurricane force winds cars blown into air valley floor covered by 45 m of rubble 28 people (campers) were killed produced waves in Hebgen Lake that swept over dam Madison Canyon slide

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6 mass movements occur everywhere… …estimate damage annually in US at $1.5 billion… …less than 1,000 deaths of 20,000 lost in natural disasters from were from mass movements not likely to be killed by mass movements, but likely to pay for effects

7 classification of mass wasting rate of movement type of material type of movement cm/year to 100 km/hour solid bedrock or unconsolidated debris flow, slide, fall, creep

8 flow: viscous fluid slide: mass remains intact (2 types: landslide; slump) fall: free-fall of material types of movement

9 fastest

10 rock fall

11 rock fall in action

12 rock fall with talus slope

13 hill gives way in coherent mass --large block moves

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15 surface of movement is concave scarp (type of slide but with rotation)

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17 submarine landslides (Hawaii) landslides on Mars

18 move slowly (viscous) 1-2 meter/hour flows: earthflow solifluction

19 earth flows and solifluction

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21 may move quickly over gentle slopes (1°-2°) flows: mud flow (mixture of debris and water)

22 mud flow at Nevada Huascaran, Peru: killed 18,000 people before

23 after

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26 dried mudflow

27 mudflow on Toutle River from Mt. St. Helens

28 flows: soil creep

29 downslope motion for creep freeze/thaw cycle

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34 permafrost: another example of freeze/thaw

35 summary: rates and types of mass wasting

36 controlling factors in mass wasting gravity (friction and slope angle) slope composition vegetation water large relief

37 gravity: 2 factors in balance 1) gravity--pulls object to center of Earth 2) friction--resists block sliding downslope component perpendicular (normal) to surface (contributes to friction) component parallel (shear) to surface (contributes to sliding) depends on angle of slope; slipperiness of slope; and magnitude of normal component of gravity

38 relief: change in elevation greater difference in relief yields greater shear forces along slopes

39 1) small amounts of water 2) excessive amounts of water water: two effects counteracts normal component of gravity …water pushed upward… reduces friction between surface material and underlying rock glues particles by surface tension--”sand castles”

40 slope composition (amount of loose rock) ….solid bedrock, unconsolidated bedrock (loose or weathered material) solid rock very stable even as cliffs…NOT stable if: has lots of fractures (cracks) is soluble (limestone) such that cavities form has layering of “wrong” orientation …bedding (sedimentary rocks) or foliation (metamorphic rocks)

41 effect of bedding planes in sedimentary rock

42 let’s be smart…recognize and prevent

43 slope composition (continued) ….solid bedrock, unconsolidated bedrock (loose or weathered material) unconsolidated material stability depends on frictional properties… is stable until maximum angle …angle of repose… is highly dependent on water content

44 angle of repose: maximum angle where friction balances gravity

45 roots stabilize loose, unconsolidated material …removal (by fire or clear-cutting) leads to mass movement vegetation

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47 prevention water, weight of house, road cut

48 improve drainage -- leads to less creep

49 modify slopes (where layering dips into roadway)


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