| Summary: | On Sakhalin Island on Sakhalin Island the area affected of avalanche processes 50%, taking into account the formation of avalanches on the slopes, covered with dense forest are 70%. The number of avalanche paths per 1 km of the valley – 7–9, per 1 km of the coastline – 56. The average volumes of avalanches are 100–10,000 m3. It is believed that the volumes of avalanches in the low mountains are relatively small. However, the field research found that, in low mountains of Sakhalin Island are formed avalanches of a volume over 1,000,000 m3 are formed. On 03.01.1991, an avalanche with a volume of 1.4 million m3 with runout distance of 3,800 m and a front height of 100 m descended on the Chamginsky Pass (the East-Sakhalin Mountains, Granichnaya Mountaine). Methods of registration of extreme volumes avalanches were: a visual checking; description the tracks of avalanches and circumstantial evidence (geobotanical, etc.). The formation of avalanches of large volume in low mountains can be explained the great depth dissection of the relief (300–1,000 m); a large amount of solid precipitation (recorded highs precipitation on Chamginsky Pass, East-Sakhalin Mountains were 333 mm per snowfall; 127 mm per day, and 43 mm per hour) and strong recrystallization of the snow pack (values of coefficients of: recrystallization of the snowpack – 0.80–0.95, secondary delamination of the snowpack – 0.50–1.0 texture of the snowpack – 0.50–0.80). The frequency of occurrence of avalanches with of a volume more than 200,000m3: in the middle of Sakhalin – 1 per 3 years, on the southern Sakhalin – 1 per 5–7 years. In low mountains, the same large avalanches form as in high mountains. Avalanche runout distance in the low mountains of Sakhalin Island exceed their values calculated on the basis of almost all existing avalanche models. Underestimation of the maximum runout distance and the volume of avalanches leads to underestimation of avalanche risks for the projected objects in the preparation of feasibility studies of investments and state ...
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