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Unformatted text preview: Day 34: Weathering, Erosion and Mass Movement * exogenic processes : driven by climate and gravity; processes operating at, or near, the Earths surface = wearing down of the landscape = slow, steady changes 1. weathering : disintegration and decomposition of solid rock 2. erosion : removal/transportation of weathered rock and soil 3. mass movement : movement of rock/soil downslope due to gravity Weathering A) Physical : disintegration, caused by external forces * frost action : water seeps into fractures and expands as it freezes, exerting pressure against the solid rock * salt crystal growth : salts dissolved in water re-crystallize after water seeps into fractures, breaking up the rock * root action : small roots work into the small fractures in rock; as plant grows, root acts as a wedge to break rock apart * thermal expansion : rock volume changes in response to dramatic temperature change, causing rock to break apart * unloading : buried rock structures are uncovered through weathering/erosion and crustal uplift; rock expands and fractures (ex. foliation) B) chemical : decomposition; rock is broken apart at the molecular level; atomic bonds broken, causing rock to be reduced in size. * solution : rock dissolves in water * spheroidal weathering : chemical weathering processes occur along fractures in the bedrock; results in spherical rock formations = chemical weathering is most effective in warm, humid climates Mass Movement * movement of rock/soil downslope due to gravity * varies in rate of motion from imperceptible to incredibly fast * slope is the primary factor; steep slopes have higher risk of slope failure * slope failure occurs when resisting forces (friction, cohesion, etc.) are reduced, allowing gravity to move material downslope * results in 25 deaths and $1.5 billion in damage in the U.S. annually * triggering mechanisms: 1. excessive rainfall/snowmelt (water adds weight and reduces friction) 2. earthquakes 3. volcanic eruption 4. changes in original slope (oversteepening) * forms of mass movement a) fall : free-falling of rock down a vertical, or nearly-vertical, slope b) flow : movement of rock/soil as a viscous fluid c) slide : movement of rock/soil as a single unit across an inclined surface ( slip surface ) d) subsidence : sinking/collapse of the land surface Day 35: Soils * natural surface layer consisting of mineral/rock matter, organic matter, and capable of supporting life * processes of weathering act to transform solid rock into soil * virtually all human activities on the landscape are influenced by soil properties * many areas of concern due to misuse of the land (erosion, depletion of nutrients, etc.)many areas of concern due to misuse of the land (erosion, depletion of nutrients, etc....
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This note was uploaded on 04/18/2008 for the course GEOL 114 taught by Professor Bradley during the Spring '08 term at Northwest Missouri State University.
- Spring '08