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Settled snow: This type of avalanche is rare and is only likely to occur when the support of the snow is removed. This may result either from loss of bond with the underlying snow, resulting, for example, from water seepage over an underlying crust, or from loss, perhaps by avalanche, of support derived from snow on the lower part of a very steep slope, the upper portion of which is covered with settled snow. Wet-snow avalanches.—New snow: A wet new-snow avalanche may occur when the snow becomes damp because of sun, rain, warm humid wind, or high air temperature, and may well be expected whenever the snow becomes sticky or sloppy. Here again, the likelihood of an avalanche will depend not only on the wetness of the snow, but also on the gradient and contour of the slope, and the bondage to the underlying snow or ground layer. The extent to which a wet new-snow avalanche will slide as a blanket or roll in huge balls will depend on how wet the snow is. Water in small quantity increases cohesion, but reduces cohesion when present in a large quantity, just as is true with dry, damp, and very wet sand. |
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