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, a rapid mass movement tha
t included fragmented cold and hot volcanic rock, water, snow, glacier ice, trees, and some hot pyroclastic material. Most of the May 18, 1980 deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche.
Uncertain: unknown or not identifiable; Debris free: Almost no debris coverage on the glacier surface; Partly debris covered: More than 10% and less than 50% of the glacier surface in the ablation are
a is debris covered. Patchy distribution; Mostly debris covered: More than 50% and less than 90% of the glacier surface in the ablation area is debris covered. Continuously distributed debris cover; Completely debris covered: Almost the entire ablation area is covered by debris. Debris covered ice;
A glacier that supports a layer of rock, dust or ash detritus on most or all of the surface of its ablation zone. In the accumulation zone any deposited debris is buried by later snowfalls, but in the
ablation zone debris remains at the surface and englacial debris is added to the surface layer from beneath as ice ablates away. The debris cover affects the rate of ablation, with very thin debris resulting in accelerated melt and debris thicker than a few tens of millimetres reducing the melting rate.
A sudden and destructive variety of landslide, in which loose material on a slope, with more than 50 percent of particles larger than sand size, is mobilized by saturation and flows down a channel or
canyon