Geog 1113 test 2 - 2/4/10 DENUDATION/DEGRADATION *A...

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2/4/10 DENUDATION/DEGRADATION **A combination of processes that wear down the Earth's crust. ** Processes : * weathering * mass movement * erosion * transportation * deposition ** Agents: * gravity * running water * wind * glaciers * coastal waves WEATHERING ** The processes by which rocks are chemically altered or physically broken into fragments as a result of exposure to atmospheric agents and the pressures & temperatures at or near the Earth’s surface , with little or no transportation of the loosened or altered materials. *Igneous and metamorphic are harder to break down than sedimentary * 2 Principle Types of Weathering: * Mechanical (or Physical) (colder and dryer conditions) * Chemical (warmer conditions) ** Mechanical or Physical Weathering **The breakdown or disintegration of rocks into smaller fragments by physical processes. With NO chemical alteration * Several Methods or types: frost action : or freeze-thaw action * As water freezes it expands some 9% by volume *This causes increased pressure within a confined space, such as a crack, joint, or fracture as the ice expands * Repeated freezing and thawing of the water, freeze-thaw cycles , may lead to fragmentation of the rock. This is also called frost-wedging or ice wedging . * Important in areas where temperature rise above and fall below the freezing point EX: High elevations and high latitudes: bare, exposed rock surfaces of mountain salt-wedging :
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* The growth of salt crystals within the cracks and pores of rock surfaces can apply increased pressure similar to ice crystals. * A process found in arid environments where salt crystals grow after water that has gotten on the rocks evaporates . * Also common along sea coasts when sea spray accumulates in the cracks or pores of the rocks and then evaporates. Hydration : * Works primarily at the grain-size level Pressure-release jointing: * Rock masses formed deep underground and thus under great pressure will expand as long as the pressure is released when the overlying material is removed by erosion * Layers of rock peel away along curved fractures parallel to the masses shape in a process known as sheeting or exfoliation EX: a batholith forms deep underground & as erosion takes away the overlying material, pressure on the pluton is reduced & it expands causing the sheeting EX: Stone Mt., GA , several areas in the Sierra Nevada Thermal weathering: *Rocks expand and contract as they are heated and cooled *Commonly seen in hot, dry areas or as a result of forest fire * Works primarily at the grain-size level; may create spalling (flaking) of the rock surface ** Chemical Weathering **Decomposition and decay of minerals in rock through chemical alteration (reactions)
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** Water is often essential **Rates of decay dependent on temperature and precipitation ** Types: spheroidal: *Water dissolves the rock’s cementing materials
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This note was uploaded on 01/17/2011 for the course GEOG 1113 taught by Professor Hodler during the Spring '08 term at University of Georgia Athens.

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Geog 1113 test 2 - 2/4/10 DENUDATION/DEGRADATION *A...

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