studyguideforfinal - Chapter 15 Mass Wasting Know the...

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Chapter 15 – Mass Wasting Know the controlling force of mass wasting ( gravity ) Know the important factors in mass wasting (water saturation, angle of repose, vegetation, earthquakes) - The Role of Water : Mass wasting is sometimes triggered when heavy rains or periods of snowmelt saturate surface materials. When the pores in sediment become filled with water, the cohesion among particles is destroyed, allowing them to slide past one another with relative ease. Thus, saturation reduces the internal resistance of materials, which are then easily set in motion by the force of gravity. - Oversteepened Slopes : Unconsolidated, granular particles (sand-size or coarser) assume a stable slope called the angle of repose. This is the steepest angle at which material remains stable. Over steepening also produces unstable slopes and mass movements in cohesive soils, regolith, and bedrock. - Removal of Vegetation : Plants protect against erosion and contribute to the stability of slopes because their root systems bind soil and regolith together. When anchoring vegetation is removed by forest fires or by people (for timber, farming, or development), surface materials frequently move downslope. - Earthquakes : An earthquake and its aftershocks can dislodge enormous volumes of rock and unconsolidated material. Intense ground shaking during earthquakes can cause water- saturated surface materials to lose their strength and behave as fluidlike masses that flow. This process is called liquefaction . Review the types (fall, slide, flow) of movement - Fall : When the movement involves the freefall of detached individual pieces of any size, it is termed a fall. Fall is a common form of movement on slopes that are so steep that loose material cannot remain on the surface ( talus slopes ). - Slide : Many mass-wasting processes are described as slides. The term refers to mass movements in which there is a distinct zone of weakness separating the slide material from the more stable underlying material. Two basic types of slide are Rotational Slides in which the surface of rupture is a concave-upward curve that resembles a spoon and Translational Slide in which a mass of material moves along a relatively flat surface such as a joint or fault. - Flow : The third type of movement common to mass-wasting process is termed flow. Flow occurs when material moves downslope as a vicious fluid. Most flows are saturated with water and typically move as lobes or tongues.
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Rates of movement (e.g., creep compared to rock avalanche) - Rock Avalanche : The most rapid type of mass movement is termed rock avalanche. Many researchers believe that rock avalanches must literally “float on air” as they move downslope. This is, high velocities result when air becomes trapped and compressed beneath the falling mass of debris, allowing it to move as a sheet (like air hockey puck). -
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This note was uploaded on 05/07/2008 for the course GEO 101 taught by Professor Wilkie during the Spring '08 term at Washington State University .

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studyguideforfinal - Chapter 15 Mass Wasting Know the...

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