Debris flow

Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally have bulk densities comparable to those of rock avalanches and other types of landslides (roughly 2000 kilograms per cubic meter), but owing to widespread sediment liquefaction caused by high pore-fluid pressures, they can flow almost as fluidly as water.[2] Debris flows descending steep channels commonly attain speeds that surpass 10 m/s (36 km/h), although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide. The largest prehistoric flows have had volumes exceeding 1 billion cubic meters (i.e., 1 cubic kilometer). As a result of their high sediment concentrations and mobility, debris flows can be very destructive.

Debris flow channel with deposits left after 2010 storms in Ladakh, NW Indian Himalaya. Coarse bouldery levees form the channel sides. Poorly sorted rocks lie on the channel floor.
Debris flow in Saint-Julien-Mont-Denis, France, July 2013
Scars formed by debris flow in Ventura, greater Los Angeles during the winter of 1983. The photograph was taken within several months of the debris flows occurring.[1]

Notable debris-flow disasters of the twentieth century involved more than 20,000 fatalities in Armero, Colombia, in 1985 and tens of thousands in Vargas State, Venezuela, in 1999.


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