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Show APPENDIX D. CONDENSED SNOW SAFETY GUIDE This guide is designed for the average ski mountaineer or winter crosscountry traveler who enters the big snow country on business or pleasure, Avalanches are the principal danger of winter mountaineering. This danger can be avoided by knowing and obeying a few simple, common- sense rules. Avalanches 1. The basic causes are steep slopes and large amounts of snow. 2. There are several kinds: loose snow avalanches, dry, damp or wet; slab avalanches, from a special kind of wind- packed snow; and combinations of the. above. 3. Avalanches occur during storms or shortly after due to rapid accumulation of new snow. k. avalanches occur during fair weather due to sun action on the surface and the deeper thawing of spring. Rain is a deep thawing agent. 5. Avalanches occur at any time due to the fracture of slabs which may be far beneath the surface. Cornices- those overhanging drifts that form on ridge crests- are similar to slab. Avalanche Weather 1. Stormy with much new snow- 10 inches or more; with high rate of snowfall- an inch an hour or more; plus strong wind action- 15 mph or more. | This is a standard avalanche combination. 2. Fair with rapidly rising temperatures, with or without sunshine, after a storm. This condition promotes sunslides and slab avalanches released by thawing. Above freezing temperatures for 36 hours in spring promotes deep thawing and wet avalanches. Rain has the same effect plus the extra weight. Avalanche Terrain 1. Slopes of 25 degrees or less seldom slide. 2. Slopes between 25 and 35 degrees occasionally slide, especially if stimulated by the cutting action of a pair of skis. 3. The critical zone lies from 35 degrees on up. In this zone slides of some sort are likely with every major storm. 4. Steep gullies are natural avalanche paths. - 139 - |