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WEATHERING, SOIL, AND MASS WASTING |
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Mass Wasting
The downslope movement of rock, regolith, and soil under the direct influence of gravity.
Examples: landslides, avalanches
- Does not require a transporting medium like wind or water
- Together with running water, mass wasting produces stream valleys
- Gravity is the controlling force of mass wasting but other factors contribute to an unstable slope.
- water acting as a lubricant
- enough water will fill the air spaces in the soil destroying cohesion of soil and allowing the particles to slide past each other; also water adds weight to the materials
- over-steepened slopes
- the angle of the repose is the steepest angle at which a slope remains stable (usually 25° to 40 °)
- vegetation removal
- the root systems of plants help keep slopes stable by protecting against erosion
- earthquakes
- large amounts of rock and unconsolidated materials can be dislodged by earthquakes and aftershocks
Classifying Mass Wasting Events
Classifying mass wasting events uses three characteristics; motion type, velocity movement, and type of material involved.
- Fall - freefall of detached pieces of any size
- Slides - material remains fairly coherent and moves along a well defined surface, maybe a fault, joint, or bedding plane parallel to the slope
- Slump - material moves as a mass along a curved surface of rupture; the base of the slope becomes unstable
- Flow - material moves downslope as a viscous fluid
- Examples: mudflows, lahars
- Creep - gradual downhill movement of soil and regolith; aided by soil disturbance; causes fences or poles to lean
- Soliflution - water saturates the soil and the mass flows downslope
