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Show - 2 - In order to follow the evolution of a given snow layer, it is necessary to construct a time profile, based on a series of pits excavated through the snow cover at periodic intervals in which the density, crystallography, temperature and other properties of the individual layers can be inspected separately. To date this technique has been carried out regularly in the western United States, Canada and Alaska in connection with snow and avalanche research stations and certain glaciological investigations. Though results are available only from a limited number of stations, they do exhibit significant variation due to climate and snow type which merit presentation and discussion. This present progress report summarizes some of the snow density data currently available at the Alta Avalanche Study Center, It will be followed by additional reports in the near future as more information is gathered from other stations and analyzed. Snow Layer Densification Figures 1 and 2 show the average time variations of snow density in snow layers observed over the course of six winters at the snow study plot at Alta, Utah, in the middle alpine zone. The curves are fitted by eye to the plotted points. In Figure 1, the plot for densification of snow below 0° C, the curve is seen to exhibit the familiar feature of very rapid density increase over the first 10 or 15 days, followed by a gradual decrease in the rate of densification. Even after a hundred days or more, a slow increase in density persists. In Figure 2, the plot for snow densification at the freezing point, the curve is displaced upward a short distance from that for cold snow, |