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21 Cards in this Set
- Front
- Back
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Driving Force
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Gravity pulls down slope
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2 Resisting Forces
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Friction resists movement
Cohension makes grains stick together |
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How does the driving force work?
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The component of the driving force parallel to the slope (F) increases as the angle increases. Once it exceeds friction (f), the mass slides
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Mass will slide if
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Force > frictional resistance + cohesion
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Solid materials
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Withstand steeper slopes than loose material
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Unconsolidated sediment is usually unstable beyond the
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angle of repose
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Steepness
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Steeper = less stable
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A little water
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helps increase cohesion (water tension helps hold particles together)
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Too much water
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reduces friction (water flows between particles)
*depends on the pore pressure of the water* |
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Water increases the
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driving force
(it adds weight) |
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How water acts with grains of material
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Capillary cohesion in the narrow space between grains pulls the grains together
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Water pressure at depth equals
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the load or weight of the overlying water
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Pressure on water in spaces between grains
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Forces the grains apart
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Vegetation increases
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the driving force (adds weight)
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Roots
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hold unconsolidated sediment together, increasing cohesion
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Plants pump water from the gorup up through their roots to transpire it through the leaves, which
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reduces the driving force and increases friction
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Slope failures
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Falls, slides, flows, creep
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Subsidence
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Regional (compaction in deltas, removal of ground water)
Karst-related (limestone dissolving, mines) |
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Shale and clay beds
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Hold water; slide-prone
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Creep
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Soil slowly slides down
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Creep explained in detail
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Freezing and thawing
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