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Show width, these originate on the upper mountain slopes as small clefts. Snow accumulates over the entire gully floor. Avalanches observed in deep gullies are mostly of pulverized snow type. Gap No. 3 and Gap No. 4 on the southwest side of Mount Ukspor are typical deep gullies. 5) Shallow cirgues ( or funnels): Rather shallow depressions on the upper reaches of the mountain side, narrowing toward the lower part, where they emerge into shallow gullies, these sometimes appear to be groups of merging shallow gullies. As avalanche sites, they are like shallow gullies, but have correspondingly larger floors, measuring several hectares, and hence give rise to avalanches of greater volume. The large cirque on the southwest slope of Mount Ukspor is an example of this type of relief. 6) ( True) cirgues: Denuded, niche- like concavities in the higher slopes, these communicate with the valleys below by deep gullies, down which the avalanches descend. Cirques can be steep enough at their upper edge ( rim) to give rise to snow cornices ( cirques on the southwest slope of Mount Aykuayventchorr), or they might show a slight, gradually increasing grade up the sides of a plateau ( Uks-poryak cirque). The floor area of cirques is measured in tens of hectares, and all of it serves as an accumulation basin for the snow. Large pulverized snow and " lump snow" avalanches arise in cirques. 7) Precipitous cirgues: Precipitous, with nearly vertical walls, the sides of such cirques sometimes rise as high as the valley walls. Because of their steepness, there is not much snow accumulation. They give rise only to " top snow," " knurled snow," and " rolypoly" ( floating) snow avalanches which die at the lower end of the cirque. Examples of this type of relief are Molebden Cirque and Gan-yeshin Cirque on Mount Tahtaravumchorr. 8) Gullies in cirgues: The sides of cirques generally show depressions much like shallow gullies. Avalanches are frequent in these comparatively small cirque- gullies, but do not dump their snow over the whole cirque floor. Since such avalanches do not involve the whole cirque, the depressions where they occur are classed separately as " gullies in cirques." Seventy per cent of all avalanche sites have a western exposure, i. e., from northwest to southwest, inclusive. The significance of the relief for avalanche frequency, type and volume can be seen from the data in Tables 15 and 16, where percentages are given for 49 avalanche sites characterized by type of relief in the districts under observation. Treated are 119 avalanches totaling 1,194,000 m3 in volume. Attention is drawn to the fact that avalanches originate in deep gullies more frequently than in any other relief feature. Deep gullies are also the only relief form in which avalanches of all types occur. - 57- |
