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Show " Knurled snow" avalanches March 6 - June 12 " Rolypoly snow" avalanches April 18 - June 9 Wet snow avalanches April 6 - May 30 The Terrain and Indications ( Signs) of Avalanching Although the presence of snow at many places on mountain slopes constitutes an avalanche hazard, the likelihood is not the same for all sites. That is to say, the slope grade is not in itself the only index of avalanche danger, because less snow is held on steep slopes and the snow here is more easily removed by wind action. In Chibin a great many avalanches, but only small ones measuring a few tens of m3, break away on 45° slopes. The overwhelming majority of large avalanches break away at 30- 45° grades, and slopes of 30° yield only isolated but large slides. The lowest break- away grade measured, 20°, was for an avalanche of wet granular snow. Snow accumulates preferentially in the depressions and cavities of the terrain, and most avalanches break away here. It is the terrain that enables one partly to assess the avalanche hazard at any given site. The conditions of snow deposition and accumulation are also dependent on the terrain, which also determines to a considerable degree the likelihood of one or another avalanche type. Let us describe those characteristic relief forms that are important in giving rise to avalanches. 1) Bare unbroken slopes: Hundreds of meters in extent, sometimes with slight breaks in grade, often covered with turf, these slopes are sites for " lump snow" avalanches, less often for those of other types. An even slope is more conducive to avalanching than other relief forms of the same grade. An example of such relief, infrequently observed in the vicinity of Kirovsk, is the west slope of Mount Aykuayventchorr, along the Chibin ( RR) branch line. 2) Slopes with cliffs: The steep places on such slopes give rise only to " top snow" and " knurled snow" avalanches. The areas between gullies on the southwest side of Mount Ukspor belong to this type of relief. No avalanches were observed on the steep, rocky slopes here. 3) Shallow gullies: Shallow depressions extending down to the foot of the mountain, these begin somewhat below the mountain tops, sometimes at the base of the peak itself. They are several times wider than they are deep; some are so wide in relation to their depth that they lose their characteristic elongated gully form. Although the entire gully floor surface acts as a snow catchment, most of the snow accumulates in the lower part, below points of sharp or abrupt grade, where the break- away nearly always occurs. Most of such sites encountered around Chibin are dangerous because the avalanche indications go unnoticed beneath the snowcover, especially where they are features of the lower slopes. Shallow gullies give rise mostly to pulverized snow avalanches. Typical of such an avalanche site is Gap No. 2 on the south west side of Mount Ukspor. 4) Deep gullies: Depressions in which the depth is equal to or greater than the - 56- |
