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Show A damp or wet snow avalanche may also start at a narrow point if release is caused by some disturbance such as a wad of snow or falling rock. However, it almost immediately spreads to its full width and is much more likely to start in that manner. Slides of this type being heavier, develop more fraction and travel more slowly. In fact the typical wet spring avalanche is slow enough so that any reasonably alert person can get out of the way* Their principal threat is to stationary objects like buildings or parked cars. In the case of damp slides, the word "slow" is a comparative term. While they may not travel at the explosive speed of a dry avalanche, any skier had better have a long start and a good wax job before trying to outrun one of them. They are second on the danger list at Alta. Because damp snow has considerable inherent stability it will cling to a steep slope until dangerous amounts build up. Since slides of this type develop maximum volume at or soon after the start, they do not need a long run* Experience has taught us at Alta that during a damp snow storm, especially if wind action is strong, the avalanche hazard rises much more rapidly, and the cycle is apt to be much more violent than with any other type of snow except slab. The most dangerous damp slides are those where release is due to simple accumulation of weight during a storm. Damp sunslides are more likely to slough cff a few inches at a time. Slab avalanches at Alta as in any other area where they take place, are the most dangerous of all. This is the only kind of avalanche which can fairly be called vindictive. Unlike other forms of unstable snow, it does not resolve the problem quickly by sliding or settling. It retains its instability for any length of time. If found on the surface, snowslab or windslab has a characteristic dull, chalky, nonreflecting appearance, but it is generally disguised under layers of later fallen snow which may themselves be perfectly stable* Release of a slab avalanche is sudden, violent, and extensive. Motion pictures of explosive-released slabs in 19^2 show practically the entire slope in motion at once. A skier caught in a alab avalanche has practically no chance to do anything for himself. He is instantly knocked off his feet, pounded by the grinding, rough-edged blocks, and carried down at greater speed than he could attain in a straight schuss. The outcome for him is purely a matter of luck, generally bad* Slab is a type of windpacked snow. The manner of its formation is not thoroughly understood. Most authorities agree that it develops on lee slopes from wind action on falling snow, rarely from snow already fallen and picked up by the wind. Contour of the surface is a necessary condition so that just the right degree of turbulence is created in the windborne mixture of air and snow. On one slope at Alta where the wind customarily blows parallel to the contour we find wind crust and other stable forms of snow interspersed with patches of slab on the lee edge -27- |