Snow, Ice, Avalanches, and Glaciers - Mountain Geography: Physical and Human Dimensions - page 170

FIGURE 4.17 Avalanches involve a great deal of force and can do significant damage. This large Idaho
snow avalanche pushed a truck of U.S. Highway 12 and into the Lochsa River. (Image courtesy of
K. Birkeland.)
Loose-snow avalanches occur most frequently in newly fallen snow on steep slopes,
where the snow cannot maintain itself through internal strength. This is common when
light, fluffy snow falls and the winds are gentle. The snow has little internal cohesion, so
slight disturbances may be enough to cause it to slide until it reaches a gentler slope.
Loose-snow slides are perhaps the most common kind of avalanche, but they are gener-
ally shallow and small and cause little damage (Figs. 4.18a, 4.19). Scores of such slides
may take place during a single snowstorm. In fact, their occurrence may be a stabiliz-
ing factor, since frequent small slides provide a continual adjustment in the snow and
can prevent major slides. The most dangerous kind happens in the spring when the
snow is wet; as they move downward, these loose-snow avalanches may gather enough
momentum and mass to cause considerable damage (Perla and Martinelli 1976: 68;
McClung and Schaerer 2006; Barry and Gan 2011).