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Show P.. M^^ r ". ' 5'' Fig. 20. Powder avalanche at Trugberg Fig. 21 ( Jungfrau region) 2. The Velocity and Flow Height of Avalanches. Spring avalanche in loose, damp snow. Calvinen ( Parsenn region) A snow layer of vertically measured thickness, h', which slides on a slope of constant gradient, - ty , sets up a frictional resistance on the base, which is proportional to the sliding area ( slip coefficient £ ) and, in turbulent flow, to the second power of the velocity, v, and to the density, y . In addition, a frictional resistance acts, which is proportional to the sliding area and to the normal pressure acting on it. Little is yet known about the friction coefficient p, = tan p . The angle of repose is usually 30° to 40°; the greatest number of avalanches occur in this range of slope inclination. According to A. Roch [ 9] destructive avalanches are seldom released on steeper slopes, since the snow trickles down successively in small amounts. On the other hand new snow and wind packing can lead to significantly greater angles of repose. A. Roch reports that for new snow the angle of movement is 17 for initial small velocities. This value lies at the upper limit, since avalanches frequently do not come to rest by themselves on very long slopes of about 10° gradient ( Dalaas Moreover, „ increases with the density. The equation [ i= y/ 2000 ( y in kg/ m3) 13°) 22 |
