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Show of the slope and seldom reaching levels of lesser grade, characteristic of small avalanches of wet snow breaking away from under cornices; 2) rollers - ( Fig. 6- 2) - elongated dumps of uniform width, or widening at the lower tip, with the main mass at the blunted fore part, the forefront showing an abrupt slope forward, less so rearward, deposited only on steep slopes, like tongue- form deposits, typical of not too large avalanches of dry, freshly fallen snow; 3) fans - ( Fig, 6- 3) - deposits of snow balls stretching down a slope, defining a fan- like shape of tracks emerging from a common point, the forefront not clearly defined and consisting of snow balls rolled ahead of main mass, typical of small avalanches caused by the rolling descent of masses of melting snow detaching upslope; 4) flattened, drawn- out cones - ( Fig. 6- 4) - cone- shaped deposits with the apex upslope, the forefront not always clearly defined because of being formed of more than one arrested snow stream or current - " shoulder", more or less uniform in thickness and slightly elevated in the mid- portion, typical of avalanches of loose windblown snow. ( This is the most frequently observed type of avalanche dump.); 5) humped, drawn- out cones - ( Fig. 6- 5) - as above, but with the snow disposed in concentric waves across the deposit, resulting in very uneven snow distribution, typical of avalanches of dense, heavy snow, dumped in separate longitudinal streams of chunks; 6) amorphous conglomerations - ( Fig. 6-) - unorganized accumulations of chunks, balls and milled snow, or irregular in contour and consisting of several separate snow streams, typical of avalanches of wet granular snow deposited in layers on uneven slopes and around obstacles, and of large avalanches of dense snow descending gullies, covering areas of several hundred m2 ( the most imposing type of avalanche dump, regardless of size of avalanche). The largest dump area we measured was 9 hectares ( 22.24 acres), truly exceptional, for the avalanche of December 22, 1936, on Mount Aykuayventchorr. Ordinarily, avalanche deposits are elongated in the final moments of slide movement, the tail consisting of a thin layer stretching as a narrow strip for tens or hundreds of meters. Avalanche Troughs When an avalanche of heavy snow from a cirque enters a gully sometimes filling it to a depth of 10- 12 m, it produces a marked effect on the underlying snow. All natural snowcover is planed off the rocks and protrusions in the terrain, and the sub- slide surface is covered with a continuous ice crust, often several centimeters in thickness. It is only under this crust that any old snow is preserved in a loose state. On its exit from the gully onto open slope, the slide at first preserves its cross- sectional relationships as it starts down slope as a high, narrow stream. The sides of this stream, having lost the support of the gully walls, collapse and are deposited laterally. The avalanche stream passes between these side ridges, which are at first merely continuations of the gully walls, flattening them to some extent, thus creating a slide trough. This avalanche trough has steep or vertical sides and a flat floor, which are sheeted with ice and furrowed longitudinally. Outside the gully the outer part - 39- |