Mass Wasting PDF

Mass Wasting Mass wasting is the action of gravity as a geomorphic agent. Mass-wasting events are commonly called landslides, but this is not a word used in technical geomorphology. There are many different ways a mass-wasting event can be triggered, such as heavy rains, snowmelts, seismic activity...

Mass Wasting Mass wasting is the action of gravity as a geomorphic agent. Mass-wasting events are commonly called landslides, but this is not a word used in technical geomorphology. There are many different ways a mass-wasting event can be triggered, such as heavy rains, snowmelts, seismic activity (such as earthquakes), and forest fires. However, no such violent event is even necessary to trigger a mass-wasting event. A mass-wasting event may be caused by an over-steepened slope. The maximum steepness that a hillside or mountainside can endure before gravity can finally move regolith downward is called the angle of repose. In other words, the moment the aggrading of sediments upon a hillside or mountainside results in a steepness greater than the angle of repose, gravity will degrade the hillside or mountainside, and the regolith will move downward. The regolith will continue to move downward until the steepness of the hillside or mountainside is more shallow than the angle of repose. Of course, geomorphic agents will continue to aggrade sediments upon the hillside or mountainside after the mass-wasting event. Again, the moment the aggrading of sediments results in a steepness greater than the angle of repose, gravity will degrade the hillside or mountainside, and the regolith will again move downward. The fastest type of mass-wasting event is called a fall. Somewhat slower than a fall is a slide or flow. The slowest type of mass-wasting event is called creep (or solifluction when glacier-related). The regolith moving during a mass-wasting event may be primarily rock, debris, earth, or mud. An avalanche is a mass-wasting event that is not necessarily glacier-related, since there are rock avalanches and mud avalanches for example. An avalanche that is glacier-related should properly be called a snow avalanche. A lahar is a mudflow composed of pyroclastic materials down the side of a volcano. After many mass-wasting events, there may be an accumulation of sediments at the base of a hill or mountain. These are called talus slopes, since the sediment itself is called talus. A mass-wasting event may leave behind a steep cliff. These steep cliffs are often called scarps, but they are more properly called escarpments.