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Show The tabulation also shows the futility of any attempt to analyze an area's avalanche hazard on the basis of gross statistics. A few of the more obvious contradictions are as follows: as 1. There were the same number of large avalanche cycles in 19^5^6. But the former had 6l percent less snowfall. However, that snow was markedly heavier and the cumulative snow depth was actually greater. 2. 19^6-^7 had J8 percent of the large avalanche occurrence of 13k"(-kS with only 68 percent of the snowfall. In this case that snow was less in weight and cumulative depth. 3. To narrow the field of view a little, March 19^7 had 71 percent of the avalanche occurrence of March 19^8 with only kl percent of the snowfall. An apparent trend in favor of avalanches in March and proportionate to the weight of snow and number of major storms reverses itself in March 19^6. To sum up, avalance occurrence does not consistently follow the season, the total snowfall, the monthly snowfall, the water content or oven the major storms. It is plain that the problem of avalanche forecasting is not going to yield to the adding machine unassisted. III. AVALANCHE CHARACTERISTICS To the victim of its power, it makes little difference what kind of an avalanche buried him. But for purposes of analysis and study, classification is necessary. The latest Swiss practice is to recognize only two types, packed snow and loose snow. This method has the advantage of simplicity but it leaves many of the possibilities uncovered. At Alta, four types are recognized: dry snow, damp and wet snow, slab, and combinations. They are further classified as to size in terms of danger to life and property: 1. Sloughs or small. 2. Medium. 3» Large or major. Dry snow avalanches are composed of loose, new fallen snow possibly drifted but not materially altered otherwise. They start at a narrow point, travel rapidly on an elongated gradually widening path, increasing in size as they descend. If of major proportions they are sometimes accompanied by destructive air blast. Being so light, the slide travels in the air as well as on the ground. Danger to the skier is as much from suffocation in this cloud of snow dust as from physical violence. At Alta dry snow avalanches are not a great problem. Snow of this type is so unstable that it begins to slide before any great depth can build up. Thus, to become large size a dry avalanche must have a very large slide path. Only a few such paths exist at Alta. These are well known and closed early when dry snowslide conditions develop. The contract is Switzerland where these slides may fall thousands of vertical feet over cliffs. Some area^ in this country can probably match that situation. |