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Unformatted text preview: Exam 2 Surface Processes Exam – November 4 th Mass Wasting Gravity • Gravity acts everywhere, pulling everything in a direction toward the center of the earth o On a flat surface gravity acts downward o So long as the material remains on the flat surface it will not move under the force of gravity o On a slope, gravity can be resolved into two components: a component perpendicular to the slope and a component tangential to the slope Mass Wasting o If the sheer component of gravity is stronger than the forces holding an object on the slope, then the object will move down-slope • Angle of repose o Each material has a different angle of repose o Sand – can go up to 42 degrees – relatively steep slope o Cement – 34 degrees o If something is on a slope and within its angle of repose, then it does not move, if it goes over the angle of repose gravity pulls things downward until the angle of repose is reestablished • Landform Development o Down slope movement of rock, regolith (rocks and soil) and soil under the direct influence of gravity o Geologic processes that often follows weathering o Combined effects of mass wasting and running water produce stream valleys • Slopes change through time o No minimum angle is required for mass wasting to occur o Most rapid and spectacular mass-wasting events occur in areas of rugged, geologically young mountains High mountains with clear signs of gravity and erosion working to bring materials downward o Mass wasting and erosional processes slowly lower the land surface o Once mass wasting occurs, the land is fresh (no vegetation or weather) so it looks very different than the surrounding areas. Over time, the vegetation will grow back though and the land will blend in. So you must look at the actual patterns of the land to determine if mass wasting occurred – hence the land is weak. • Controls and Triggers of Mass Wasting o 1- Role of water Diminishes particle cohesion (friction) • Saturates many particles, and separates then so the water can go between particles, if too saturated then the particles can’t hold together anymore • Causes the angle of repose to decrease significantly Water adds weight o 2- Oversteepening of slopes – slope angle Stable slope angle (angle of repose) is different for various materials Oversteepened slopes are unstable • When roads are carved into the sides of mountains, then the slope of the mountain is too steep, over the angle of repose, so erosion and gravity pulls the rocks of the mountain down onto the road o 3- Removal of anchoring vegetation Vegetations has roots which make the slopes more stable Removal of vegetation weakens the slope o 4- Earthquakes Can cause liquefaction – water-saturated surface materials behave as fluid-like masses that flow • Mass Wasting structures o Source area – where the material leaves o Deposition area – where the material is accumulated • Classification of Mass Wasting Processes o Type of material Mud, earth rock o Type of motion Fall...
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This note was uploaded on 03/05/2011 for the course GEOL 101 taught by Professor All during the Fall '08 term at George Mason.
- Fall '08