2012 年 30 巻 p. 9-23
Observation stations were established on the east side of Mt. Gongendake, central Japan, in a warm snowy region where air temperature often exceeds 0°C in winter. Meteorological data were measured and avalanche events were recorded using a seismometer and three video cameras. Over four winters, 1504 avalanche tremors and 727 avalanche video images were recorded. The video images included 83 dry surface avalanches, four dry full-depth avalanches, 157 wet surface avalanches, and 483 wet full-depth avalanches. Among these avalanches, 431 were on slope S1, where a disastrous avalanche occurred on January 26, 1986. Wet avalanches represented about 88% of the avalanches and took place when the air temperature was high. Approximately 92% of dry surface avalanches occurred while snow was falling. When dry surface avalanches occurred, calculated snow stability index (SI) values were below 4 and conditions for avalanche release from within the snow cover were satisfied. Wet avalanches occurred frequently during and after March, when the air temperature continuously exceeded 0°C, and even occurred in January and February when the air temperature was high. Wet full-depth avalanches increased in frequency as snowmelt increased. Starting in mid-March, most avalanches were wet full-depth avalanches, whereas in April only wet full-depth avalanches occurred.
