Landslides - Flashcards
34 Cards in this Set
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Gravity
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The driving force for all types of mass wasting and mass movements
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mass movement
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slow or rapid downslope movement of regolith or rock materials under the influence of gravity
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colluvium
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gravity derieved loose, incoherent regolith or rock material at the foot of a slope or cliff (i.e. Talus)
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Perpendicular Component
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A component of gravity that acts as Right angles to the slope and tends to hold objects in place
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Downslope component
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A component of gravity aka Tangential Component that acts parallel to and down the slope and causes an object to move downslope
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angle of repose
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maximum angle at which unconsolidated granular materials can be piled; controlled by particle size, shape and moisture content
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High intensity and/or Long duration rainfall, earthquakes and rapid snow melt
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The 3 triggering events for mass movements are...
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Removal of Lateral Support
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Occurs naturally by stream, wave & glacial erosion; caused by human activites (i.e. road building) It increases shear stress by oversteepening slopes
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Reduce
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Geologic/rock structures ________ shear strength.
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Rainfall Intensity
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The amount of rainfall per unit time (i.e. inches/hour)
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head searp
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may have more than one; often steep-sided; forms bare, detachment area (top most part)
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Chute/track
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erosional path that landslide debris takes as it moves down slope (mid-part)
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toe
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area at the base of scar which is depositional; often has hummocky surficial appearance and is fan-shaped in map/aerial view (lower part)
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Type of Movement
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Geometry and mechanics (i.e. bedrock material or regolith amterial, which can be fine-grained or coarse-grained)
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Slides
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relatively rapid translational type of mass movement in which a coherent mass of bedrock or regolith material moves downslope along a flat, planar surface. Most common in steep mountainous areas
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Slumps
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Relatively slow rotational type of mass movement in which a coherent mass of bedrock or regolith material moves downslope along a curved, concave-upward, spoon-shaped surface. Usually fine-grained regolith materials or weak rocks
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Flows
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slow to very rapid type of mass movement in which regolith material moves downslope as a viscous, water-saturated, slurry-like fluid. Rate of movement depends on relative proportions of solid regolith material and water on the physical-chemical properties of regolith
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Solifluction
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Very slow, water saturated regolith moves downslope in sheets and loves. Requires only very gentle to moderate slopes; common in permafrost areas. (i.e. Lewis Hills, Gros Morne National Park, Newfoundland)
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Avalanche
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Extremely rapid type of mass movement in which bedrock or regolith material moves downslope as a granular flow on a cushion of air
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Composite
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Combo. of 2 or more types of mass movements over space and time (i.e. earth slump may convert to an earth flow downslope with addition of water)
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Reduces
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Retaining walls with drainage pipes _____ shear stress
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Improved Drainage; increases
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Avoid water buildup with drains or perforated pipe, de-water. It _______ shear strength-engineering approach
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Slope Reduction/Removal of Slope Materials
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cutback slopes, terracing/diversion
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Increases
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Rock bolts for rock slopes ______ shear strength
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Increases
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reforestation _______ shear strength. (i.e. deforested hill slopes in Central himalaya, NEPAL)
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Himalayas
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Earthquake prone, highest mountain range on earth, very high topographic relief; highly fractured rocks providing zones of weakness.
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mass wasting & mass movements
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Important agents in the erosion-transport deposition process portion of the rock cycle; can be very slow or extremely rapid
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Shear Stress
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(Driving force) causes movement of a mass of rock or regolith to move parallel to a slope
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Horizontal
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Gravity holds an object in place by pulling it in a direction perp. to the surface on a ________ surface
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Shear Strength
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(Resisting force) internal resistance of a body to movement. Factors inherent in a body of rock or regolith like cohesion b/t particles and binding action of plant roots; friction b/t objects contributes to this
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increases
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As a slope becomes steeper, the downslope or tangential component _______ relative to the perpendicular component so shear stress also _______
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remain in place
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if resisting force (shear strength) exceeds driving force (shear stress), material on a slope will.......
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move downslope
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v
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driving
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angle of repose is related to the _______ forces
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Landslides - Flashcards