OCR Text |
Show Introduction Many of the mechanical and thermal properties of snow significant to avalanche formation are related partly or largely to snow density ( See for instance: 1, 2, 3i 4). The values of snow density which can be expected in the ordinary course of snow cover evolution, beginning with freshly fallen snow and continuing through the winter and spring months, are thus of considerable interest to avalanche forecasting. These density values are also significant to the problems of evaluating and forecasting runoff from snow melt. Even the most cursory examination of snow density records shows that this quantity is highly variable with time and from one climatic zone to another. The standard U. S. Weather Bureau evaluation of density of new- fallen snow as 0.10 g/ cnr is only a very broad mean value, for new snow densities have been observed ranging from 0.01 to as much as 0.35 g/ cm or greater. This initially highly variable quantity is subject to further variations during the course of snow layer densification. Temperature, crystals type, superimposed load and temperature gradient all play a part in determining the ultimate density value a given snow parcel may acquire at a given time in the course of its metamorphisnu Mean density values for an entire snowcover are available in profusion from the results of periodic snow surveys carried on by Government and private agencies throughout the western United States. While useful from the standpoint of water forecasts, these mean densities yield little information about the densification processes in a given snow layer, for they are determined from the weight of a single snow core colleated from top to bottom of the snow cover. The snow thus weighed includes layers at the bottom of the snow cover which may be months old, as well as newly fallen snow of low density at the surface. |