SOME CHARACTERISTICS OF ALPINE PERMAFROST, MT-DAISETSU, CENTRAL HOKKAIDO, NORTHERN JAPAN

Alpine permafrost occurs on the flat summit of Mt. Daisetsu, which is located in central Hokkaido, northern Japan at an altitude of 2200 m a.s.l. Under present climatic conditions, the ground surface temperature is one of the major controlling factors in the distribution of permafrost on Mt. Daisetsu. The mean annual air temperature is -3.8-degrees-C suggesting the possible occurrence of alpine permafrost. High precipitation as snow fall in winter affects the ground surface boundary temperature, which, in turn, affects alpine permafrost. Due to the prevailing winter westerly wind, the ground surface at the flat summit is kept snow-free and the ground is exposed to severe winter cold. At these locations, the frozen ground surface tends to contract. The contraction cracking process was examined in a quantitative manner based on the results of both field and laboratory experiments. The depth of permafrost was estimated by geo-electric resistivity survey. On the flat vegetation-free summit, the lower boundary of permafrost was inferred to be 8.5 m deep.