Chapter 7 Notes.docx

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University of Manitoba
Geological Sciences
GEOL 2390
William M.Last

Chapter 7 Notes Slope Processes, Landslides, and Subsidence mass wasting comprehensive term for any type of downslope movement of earth materials, refers to a downslope movement of rock or soil as a more or less coherent mass, also refered to as landslides subsidence a type of ground failure characterized by nearly vertical deformation or the downward slinking of the earth materials free face has a high cliff with a straight nearly vertical slope segment, does not have surface cover of soil common for hard rock talus slope rock fragments that fall from the free face and accumulate at its base rotational slides sliding along a slip plain producing slump blocks, large deep and associated with complex movement translational sliding downslope movement of earth materials along a planar slip plane such as a bedding plane or fracture soil slips type of translational slide, shallow slide in soil over rock that occur parallel to the slope, slip usually occurs in colluvium (mix of weathered rock and other material) rock fall free fall of earth materials form a free face or cliff flows downslope movement of unconsolidated (usually saturated) materials in which particles move about and mix within the mass creep very slow flow of soil or rock earthflow origionates on a slope where soil partially liquefies and runs out, source area becomes bowl shaped depression and the depositional area spreads out at the toe of the slope (hour glass shape) debris/mud flow a mixture of rock, soil and organic matter that mixes with air and water to flow rapidly down slope , debris flow has less that 50% fines (silt and clay), mud flow has greater than 50% debris avalanche a very rapid to extremely rapid debris flow, can cause catastrophic damage and loss of life lateral spread occurs nearly on flat slope, starts with liquefaction of silts, clays, or fine sands during earthquake shaking or other disturbances start suddenly and then slow drastically slip planes surfaces of weakness in the slope of material (foliation planes, bedding planes and fractures) safety factor slope stability is evaluated on the computation of this number, the ratio of the resisting forces to the driving forces, greater than 1 stable, less than 1 unstable, these forces are not static Varibles effecting - type of earth materials driving and - slope angle and topography resisting forces - climate - vegetation - water - time climate effects seasonal patterns of weather determining timing of water and vegetation capable of growth vegetation effects cover that cushions impact of rain, facilitates infiltration, root systems add stability, adds weight to t
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