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Show - 5 - cause density increases to persist throughout the winter, as is the pronounced case on the Blue Glacier, in contrast to the nearly static state of the high alpine snow layers. It seems reasonable to conclude that these curves of snow layer density as a function of time are a distinct climatological feature of a given region, encompassing as they do the effects of initial snow types, compaction and temperature. New Snow Density The role of new snow density in establishing the point of departure for the densification curves is mentioned above. This point of departure is taken as the 24- hour new snow density, or the mean density of snow which has accumulated for a period of one day. ( See revised Handbook ( 5) for methods of determining this value.) This is a more or less arbitrary departure point selected for convenience of comparision with available records. Snow densification in fact begins from the moment of deposition, and appreciable increases in deposited snow density often take place within a single 24- hour period. The true new snow density which reflects prevailing atmospheric conditions at the moment of deposition is thus often considerably less than the mean value obtained as the 24- hour new snow densityo To obtain true new snow density, a container of known volume must be exposed during snowfall, allowed to fill with undisturbed deposited snow and then be weighed. Dimensions of the container must be such that it is filled within two or three hours at reasonable snowfall intensities if density increases accompanying settlement are to be avoided. Very few data are available on the range of true new snow densities in different climatic regions. Such records have been collected at the Alta Avalanche Research Center as a part of the regular hazard forecasting |