Some of the features of the avalanche deposits have been described previously (Crandell and others, 1984). My subsequent studies have revealed additional information, presented here, concerning the extent, volume, and mode of emplacement of the debris avalanche. A concluding section of this report discusses how the lengths of very large volcanic debris avalanches can be anticipated.
The term debris avalanche is used here to refer to the sudden and very rapid movement of an incoherent, unsorted mass of rock and soil mobilized by gravity (Schuster and Crandell, 1984). Movement is characterized by flowage in a dry or wet state, or both. Debris avalanches commonly originate in massive rockslides which disintegrate during movement into fragments ranging in size from small particles to blocks hundreds of meters across. If the avalanche has a large content of water and fine material, this material may continue to flow downslope after the coarser parts of the avalanche come to rest. Thus, the texture and behavior of a debris avalanche may change between its inception and the final stages of emplacement.
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