Mass Movement Events

A variety of mass movement events, while strictly not fluvial events, behave in a similar way to floods (Carson, 1976). The gravitationally fueled downhill movement of poorly consolidated regolith results from the introduction of meteoric water that adds weight and decreases hillslope cohesion. These events can do significant damage. Several types of mass movement events are composed of a larger percentage of sediments than a typical stream. Events such as mudflows, or lahars, commonly may approach the viscosity and velocity of streams. Valleys can be filled with fine-grained sediments as the deposits dewater following the initial surge of water and sediment. A variety of factors lead to mass movement events. The removal of plant cover by fire may expose soil surfaces so that infiltration rates may increase and lead to the accumulation of water along failure planes in the regolith. In areas with a subtropical wet-dry climate, such as the Mediterranean climate type, the burning of plant cover during the dry season and a subsequent wet season before the reestablishment of plant cover leads to mass wasting events (Rice et al., 1969; Campbell, 1975).

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