| To clarify the meteorological conditions for occurrence of wet snow avalanches in Hokkaido located in the northern part of Japan、 analysis of avalanche cases have been carried out using avalanche examples occurred on roadside slopes in the past 11 years. The 123 wet snow avalanche cases、 including of 65 full-depth avalanches and 58 non full-depth avalanches (e.g.、 soft slab avalanches)、 were used in this study. The air temperature、 precipitation and snow depth used in this analysis were observed at time interval of 1 hour in the nearest observational station of avalanche site.[*] The results revealed that the conditions for occurrence of wet snow avalanches differed in the period of earlier and later winter season. In January、 air temperature is commonly subfreezing and snow depth is not yet its maximum、 wet snow avalanche tends to occur with rainfall but increasing the air temperature was not remarkable. In March、 snowpack will start to be melted、 most of wet snow avalanches were associated with the increasing air temperature above 0 degree Celsius and occurred as full-depth avalanches. In February、 have commonly the minimum of air temperature and the maximum of snow depth in the winter season in Hokkaido、 both the rainfall and the increasing air temperature caused the wet snow avalanche、 but rainfall induced mainly non full-depth avalanches when snow depth exceed about 1.5 m. This suggested that the seasonal change in conditions for occurrence of wet snow avalanche in Hokkaido will be affected by seasonal changes of snow properties. |
