Chapter 16 - Chapter 16 Weathering Erosion Mass Wasting and...

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Chapter 16 Weathering, Erosion, Mass Wasting, and the Rock Cycle- - Erosion  and mass  wasting  are processes that loosen and transport soil and rock downhill or  downwind. - Erosion  generally refers to processes that remove weathered Earth materials on  grain-by-grain basis, usually by moving currents. - Mass  wasting  involves transport of weathered and un-weathered Earth  materials in  larger amounts and as large single events. - These events are usually driven by gravity and the tendency of Earth materials to move  downward. Both processes carry away weathered materials and deposit them elsewhere; thus  exposing fresh, unaltered rock to weathering. - Weathering  is one of the major geologic processes in the rock cycle that shape and alter the  Earth’s surface, converting all kinds of rocks into sediment and forming soil. - Material can either be weathered physically or chemically. - There are 4 main controls on weathering that effect the manner and rate: 1) The properties of the parent rock 2) The climate 3) The presence or absence of soil and vegetation 4) The length of exposure to weathering Weathering Rate Slow ----------------------------------------------------> Fast Properties of parent rock Mineral solubility in water Low Moderate High Rock structure Massive Some weakness Fractured Climate Rainfall Low Moderate High
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Cold Temperate Hot Presence of soil and vegetation Thickness of soil layer None Thin/moderate Thick Organic content Low Moderate High Length of exposure Short Moderate Long -  The properties of the parent rock affect the weathering because: 1) Various minerals weather at different rates 2) A rock’s structure affects its susceptibility to crack and fragment. - Given enough time, every rock will decay. - The climate affects weathering because: - High temperatures and heavy rainfall promote faster chemical weathering. - Whereas, cold and dry climates slow the process. * In cold climates water can’t dissolve minerals because it is frozen. - In contrast, climates that minimize chemical weathering may promote much  faster  physical weathering. * For example, frozen water may act as a wedge to widen fractures. - The presence or absence of soil plays its part in weathering because: - Soil is composed of fragments of bedrock, clay minerals, and organic matter. * Soil is a positive feedback process, meaning that the product of the  process advances the process itself. Meaning once soil forms, it begins to  work as a weathering agent on the rock that is still there, the more soil, the  faster the weathering. - Soil retains rainwater, and it hosts a variety of vegetation, bacteria, and other 
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This note was uploaded on 04/30/2008 for the course GEOL 120 taught by Professor Maglouihlin during the Spring '08 term at Colorado State.

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Chapter 16 - Chapter 16 Weathering Erosion Mass Wasting and...

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