OCR Text |
Show - 5- Deeper snowfalls are presumed to yield higher densities for the 24- hour measurement because weight of the upper layers will tend to compress and den-sify the lower layers of the snowfall. In order to test this presumption, Stevens Pass new snow densities are plotted as function of corresponding depths in Figure 7. Data from Stevens Pass are chosen because this station has the greatest number of deep 2' f- hour snowfalls. Ali data for the four year- period 1951- 1955 are plotted. Due to space limitations on the graph, only snowfalls in excess of 15 inches are plotted for the years 1956- 1961. The resulting plot indicates that there is no very clear relationship between depth of snowfall and its density. For snowfalls of less than 7 inches, there seems to be no relationship at ali. Above 7 inches, there is a tendency for density to increase with snowfall depth, but many excep-tions exist. The deepest 24- hour snowfall yet recorded at Stevens Pass, 28 inches, had a density of only 0.05 gm/ cc. The initial presumption seems to be rather poor: higher densities are not rigorously associated with deeper snowfalls, and cause of the pronounced skewness in the Stevens Pass density distribution curve must be sought in other climatological or storm characteristics as well as in deep snowfalls. One other characteristic of Figure 7 deserves notice. There appears to be a forbidden zone below whose boundary plotted density- depth points do not fali. This boundary is approximately defined by the curve y u 0.0012x + 0.015, shown in the Figure as a dashed line. Physical significance of this boundary must be sought in the mechanical strength of interlocking crystals in felt- üke, fluffy new snow. For any given depth of this new snow type which leads to the lowest densities, there must be a eertain minimum density beneath which the snow tends to settle immediately under its own weight. There is no reason to believe the boundary curve has |