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42 Cards in this Set
- Front
- Back
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mass wasting/movement (3) |
- downslope motion of rock, soil, sediment, snow, and ice - driven by gravity - characterized by wide range of rates
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slope stability |
balance between downslope force and resisting force |
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downslope force |
gravitational pull |
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resisting force |
material properties that resist motion |
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when does slope failure occur |
when downslope forces prevail |
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3 downslop forces |
- weight of earth materials - weight of added water - weight of added structures |
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types of resisting forces |
cohesion (chemical bonds, electrical charges, surface tension), friction |
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angle of repose |
due to particle size and shape and the surface roughness |
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angle of repose of: a) fine sand b) coarse sand c) angular pebbles |
a) 35 degrees b) 40 c) 45 |
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mass movement triggers |
- natural and anthropogenic - Shocks, vibrations, and liquefaction - Changes in slope strength - sometimes nothing
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why do mass movements occur |
- destabilizing events trigger slope failure - slope destabilization through loaded and angle - changes in slope strength |
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slope destabilization through loading |
adding weight to the top of a slope - water from rain or humans - materials |
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slope destabilization through angle |
steepening of a slope beyond the angle of repose - river incision - excavation for building/roads |
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3 causes in changes of slope strength |
- weathering (creates weaker regolith) - vegetation (stabilizes slopes) - removing vegetation (slows removal of excess water, destroys effective stabilizing mechanism in roots, common after forest fires) |
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role of water |
- surface tension of water causes cohesion of grains if only a film is present, causing increase in cohesion - any increase in water pressure will push grains apart, leading to flowage of unconsolidated materials |
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classification of types of mass movement based on (4) |
- type of material - velocity of movement - nature of the mass - environment
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types of mass movement from slowest to fastes |
- creep, solifuction and rock glaciers - slumping - lahars and mud flows - debris flows - rockfalls and slides |
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creep |
- slow downhill movement of regolith - due to seasonal soil expansion and contraction through wetting and drying, freezing and thawing, and warming and cooling
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movement of grains in creep |
- grains move perpendicular to slope upon expansion - grains move vertically downward upon contraction |
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evidence of creep |
- tilting of trees, telephone poles, retaining walls, foundations, tombstones |
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slumping |
- sliding of regolith as coherent blocks - slippage occurs along failure surface - variety of sizes and rates of motion |
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failure surface |
spoon shaped surface where slippage occurs |
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distinctive features of slumps |
- head scarp - upslope cliff face |
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where are slumps common |
along seacoasts and river cuts banks |
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mudflows, debris flows, lahars |
- h20 rich movement - variety of speeds - tend to follow river channels down valley - spread out into broad lobes at base of slope - essentially unlimited competence |
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mudflow |
- slurry of water and fine sediment - common in tropical settings with abundant rainfall |
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debris flow |
mudflows with many large rocks |
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lahar |
- volcanic mud or debris flow - ash - water from heavy rains or melted glacial ice |
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rock and debris slides |
- sudden movement downslope |
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rock slide |
- slide consisting only of rock |
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debris slide |
- slide comprised mostly of regolith - movement down the failure surface is sudden and deathly - slide debris can move at 300 km per hour on a cushion of air |
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vaiont dam |
- disaster in italian alps - limestone over shale in a deep synclinal gorge - oct. 9, 1963 - 600 million tons of limestone slid into reservoir - resulting wave destroyed villages - killed 2600 people |
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avalanches |
- turbulent clouds of debris and air - snow avalanche oversteepened snow that detaches - tend to reoccur in clearly defined avalanche chutes |
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rock falls and debris falls |
- vertical freefall of mass - bedrock or regolith falls rapidly downward - when blocks impact, they fragment and continue moving - talus blocks pile up at the base of the slope |
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submarine mass movements |
- much larger than land-based mass movements - mass movements tied to tsunamis |
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preventing mass movements |
- revegetation - redistributing mass by terracing - regrading - drainage - engineered structures - controlled blasting |
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2 positive effects of revegetation |
- removes water by evapotranspiration - roots help to bind and anchor regolith |
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redistributing mass by terracing |
- removes some of the mass loading a slope - catches debris |
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regrading |
reshaping slopes below the angle of repose |
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drainage |
dewatering reduces weight and increases strength |
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engineered structures |
safety structures can be built to improve slope stability or to reduce movement hazards, such as retaining walls or covers |
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controlled blasting |
surgical removal of dangerous rock |
