Video and seismometer observations of avalanche characteristics in a warm snowy district

. Introduction Kazuya AKIYAMA , Masaaki HANAOKA and Toshiya TAKESHI Video and seismometer observations of avalanche characteristics in a warm snowy district 9 Bulletin of Glaciological Research ( ) Japanese Society of Snow and Ice Niigata Experimental Laboratory, Public Works Research Institute, Arai, Japan [Now in Sabo Technical Center, Chiyoda-ku, Tokyo, Japan] Niigata Experimental Laboratory, Public Works Research Institute, Arai, Japan [Now in Shinjo O ce of River, Shinjo, Japan] Public Works Research Institute, Tsukuba, Japan (Received August , ; Revised manuscript accepted January , ) Observation stations were established on the east side of Mt. Gongendake, central Japan, in a warm snowy region where air temperature often exceeds in winter. Meteorological data were measured and avalanche events were recorded using a seismometer and three video cameras. Over four winters, avalanche tremors and avalanche video images were recorded. The video images included dry surface avalanches, four dry full-depth avalanches, wet surface avalanches, and wet full-depth avalanches. Among these avalanches, were on slope S , where a disastrous avalanche occurred on January , . Wet avalanches represented about of the avalanches and took place when the air temperature was high. Approximately of dry surface avalanches occurred while snow was falling. When dry surface avalanches occurred, calculated snow stability index ( ) values were below 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 , 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 midMarch, most avalanches were wet full-depth avalanches, whereas in April only wet full-depth avalanches occurred.