OCR Text |
Show Figure 10. Avalanche hazard created by forest fire. The Europeans consider reforestation to be one of the most important phases of the avalanche hazard control program. However, it is a mistake to consider all forested areas as safe. Scattered timber is no particular deterrent. The Bell Mountain slide in Colorado, Argenta in Big Cottonwood Canyon in Utah, and the Echo Lake avalanches in California all originate in timbered areas. In fact, a scanty tree cover often seems to augment the type of wind action which produces slab avalanches. Exposure Exposures have considerable influence. Southerly slopes favor the avalanches produced by thawing. Loose snow avalanches are more common on northerly exposures. Cornices habitually form along ridges and crests lying at right angles to the prevailing wind. Lee slopes are the most probable locations for overloads of wind- driven snow and the formation of slab. On the other hand, snow is transported from the wind- beaten slopes and that which remains is thoroughly packed and stabilized. Climate and Weather Climate and weather are the other basic ingredients in avalanche hazard. The terms are used here in a restricted sense. For our purposes they include only those items with a direct bearing on avalanche hazard: wind, snowfall, temperature, and storm characteristics, " Climate" indicates these factors on a long- term basis, an entire season or a period of years. " Weather" indicates the same items on a short- term basis, months, weeks or days. - 25 - |