OCR Text |
Show i and d are geometrical dimensions of the ledge. Utilizing Equation 2, A. G. Balabuyev and G. K. Sulakvelidze ( 1947) constructed avalanche diagrams from which it is possible to determine the slope angle, the avalanche hazard for a given type of snow, and the critical thickness of the newly fallen snow. K. S. Losev ( I960) proposed a method for calculating the time of onset of the avalanche hazard for freshly fallen and wind transferred snow by dividing the critical thickness of the snow cover by the rate of accumulation. Although his method is correct in principle, it is practically impossible to measure the physical- mechanical properties of snow in the release zone that are required in his formula for critical thickness. It may be worthwhile to simplify Losev's approach by introducing empirical relationships for each avalanche- threatened region; however, such relationships are not ci ted by Losev. All of the above methods for determining the avalanche hazard according to formulae for the critical thickness of the snow are based on special conditions and are therefore only applicable when these conditions apply. In our view, their chief shortcomings are: they do not predict when the snow cover reaches its critical value, and that they require inaccessible measurements to be made in the avalanche release zone of physical- mechanical properties and slab dimensions. Therefore, the practical application of all of these relationships becomes extremely inconvenient. Other authors ( Krasnosel1skii, 1963; Moskalev, 1963) relate empirically the avalanche hazard with the physical- mechanical properties of the snow. E. B. Krasnosel'skii assumes that the instability of a slab depends on the ratio of the shear stress ( £ * ) to the shear strenqth ( £. ) of the underlying surface of the slab fc Ko=-^ < 7) where K/\ o is the coefficient of the avalanche hazard and for |/ • I the avalanche hazard is absent; for KAO "^ I avalanches may be induced artificially; for dry snow I ^ kA0 - £ . indicates an avalanche danger in winter months; for wet snow t-- KK0^ 5 indicates an avalanche danger in spring months. - 4- |