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Unformatted text preview: 10-20-09 Ch 16:Mass movements Landslide scars: areas where there was a landslide & removal of vegetation Sliding: angle, surface, water Why do slopes fail: gravity greater slope, the greater gravity force and the block slides faster. Angle of repose- no mater how much sand you pile upon, the angle will stay the same, but the base will spread out. Slopes want to keep that same angle, when ever we change the slope, we make it unstable Fine sand: 35* Coarse sand: 40* Angular pebbles: 45* Weathering weakens rocks, lowering slope stability Chemical weathering Rock when solid is held by chemical bonds, when its broken down its held only by friction Failure surface: A slope is likely to fail along a plane of weakness Wet clay, wet unconsolidated sand, surface parallel joints, weak bedding planes (shales), foliation planes Weakest: What t riggers slope failure: Precipitation-rain fall makes ground heavier, increases down slope force, may slide down further.. weakens bonds between sediments, resisting forces decrease Water- a little water increases cohesion between grains, a lot of water decreases cohesion Changes in land use- cities take away parts of land can make less...
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This document was uploaded on 02/01/2010.
- Fall '09