Debris Avalanche 4
Debris Avalanche 4 : A rapid and unusually sudden sliding or flowage of unsorted masses of rock and other material. As applied to the major avalanche involved in the eruption of Mount St. Helens (1980), a rapid mass movement that included fragmented cold and hot volcanic rock, water, snow, glacier ice, trees, and some hot pyroclastic material. Most of the May 18 deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche. (Foxworthy and Hill, 1982). The very rapid and usually sudden sliding and flowage of an unsorted mixture of soil and weathered (altered) rock (Gardner, et.al., 1995). Moves away from a volcano at high speed
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