Week 12-13 Friday, April 13, 2007 12:41 PM CHAPTER 16: MASS WASTING • Includes all processes by which rock/soil move downhill under influence of gravity. • Is a consequence of weathering and is important part of general erosion, especially in mountainous areas • Human interference can cause severe effects. In the US excavation for buildings/ homes causes more soil to be transported than by all natural processes. • What factors control rate and amount of mass wasting? 1.Nature of rock/ soil- what type is it? 2. Steepness and stability of slope. 3. Amount of water in the materials. • See table 16.4 o For unconsolidated material- angle of repose is critical. Is the maximum angle from the horizontal that material will lie without cascading down. Depends on shape/size of material/grains and the degree of wetness o Steepness of slope for rocks depends on the type of rock and degree of weathering. • Softer shales and volcanic ash weather to gentle inclines. • Harder sandstones, limestone, granite, etc weather to almost vertical cliffs. • What triggers mass movements? o If the type of material, moisture and the steepness of the slope are right, heavy rainfall, earthquakes can be triggered. o ---- not responsible for rock mass movements- 388-394 • For unconsolidated material: look to soil creep- slow downhill movement of loose material. (about 1-10mm/yr) . Other forms faster, slump, debris slide etc- not responsible for details. o Natural landslides: • Case in western Wyoming • Can cause widespread devastation. o Mass wasting common in all plate tectonic settings. Most obvious near convergent plate boundaries, where high mountains are formed. Also occurs on ocean beds.
o Mans activities contribute to erosion and mass wasting- especially cutting away vegetation and building strip malls. CHAPTER 17-- GROUNDWATER • Following rainfall, part of the water flows off at surface into streams- chapter 18- some of the water percolated into the ground and forms a reservoir- groundwater. • At the earths surface, about 96% of water is salty- in the oceans. • Of the 4% fresh water, reservoirs are in order of importance: a. Glaciers and polar ice b. Groundwater c. Lakes and rivers d. Atmosphere and biosphere • There is a balance between the level of water in the oceans, evaporation of this water and precipitation by rain/snowfall. This is called the Hydrologic Cycle . •
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- Spring '07
- Hydrology, Aquifer, stream, River