Mass wasting

In geology, mass wasting is the process by which rock and regolith move downslope.

Related Topics:
Geology - Rock - Regolith

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This process is greatly accelerated on Earth in the presence of water, both as liquid and from the action of water as it freeze fractures rock. Mass wasting may also occur underwater in the form of underwater landslides, debris flows, slumps, and so forth.

Related Topics:
Earth - Water - Freeze fractures

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As an erosional process, mass wasting reduces the size of rocks while they are in transit while reducing their potential energy by bringing them closer to the center of the planet.

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Mass wasting may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilized the surface. It may also occur at a very high rate of speed, such as in rockslides or landslides, with disastrous consequences.

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There are several types of mass wasting, including:

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• Rock and debris falls
• Rock and debris slides
• Slumps
• Slurry flows
• Granular flows
• Rock glaciers
• Frost heave
• Gelifluction

Definition: Mass wasting is the downslope movement of rock, regolith, and soil, under the influence of gravity. Also called mass movement.

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Angle of repose

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Refers to loose, unconsolidated materials (gravel, sand, soil, etc.). The angle of repose is the angle at which loose material sits at rest. Typically 25 - 40 degrees.

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If a slope is articficially over-steepened (by man - such as in road cuts and excavations), the material will become unstable and begin to move downslope.

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Water is important; it adds weight, which leads to instability. It also lubricates loose material, and starts it moving.

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Water is in the pore spaces of the materials (i.e., between the grains). If pressure is applied (weight of the material?), water tends to move because it is incompressible. This is termed "pore pressure".

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In addition, some types of materials shrink and swell as they are wetted and dried. For example, a type of clay called montmorillonite clay expands when wet and shrinks when dry. It causes soil instability and can lead to mass wasting or downslope movement of soil.

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