北海道大雪山北海平における凍結割れ目多角形土の冬期観測
1986 年 59 巻 11 号 p. 654-663
詳細
1986 年 59 巻 11 号 p. 654-663
Large scale frost-fissure polygons are spread at Hokkai-daira plateau, Daisetu volcanic massif, central Hokkaido. In order to ascertain actual frost cracking in the frost-fissures, the authors measured seasonal changes of the width of frost-fissures, ground temperatures and snow cover from September 1984 to September 1985. Main results obtained are as follows;
1. As snow tends to be almost completely blown away by strong wind, snow cover affects the ground temperature only slightly.
2. The annual ground temperature alternations at 1m-depth ranged at least from +0.0_??_1.2°C to -13.6_??_14.8°C, suggesting the existence of permafrost underneath.
3. Horizontal distance changes between the two stakes across frost-fissures from fall 1984 to winter 1985 indicate that the width of frost-fissures increased in winter by 1cm. And frost cracks, about 1cm wide at the surface, occurred by mid-Februauy on the surface of snow and ice which covered or filled in frost-fissures. Therefore, frost-fissure polygons at this site are most likely active.
4. Considering the present climatic conditions of this area, the cross sections of frostfissure and above-mentioned results, we suggest that the frost-fissure polygons at this area are soil-wedge polygons.
