Degradation of Éxtra-zonal Permafrost near anoko Dam, Oketo Town, Hokkaido, Northern Japan

Abstract

Ground temperature monitoring near Kanoko dam, Oketo town, Hokkaido, has been conducted since 1987. Ground ice was discovered in 1979 at the site where annual mean air temperature is estimated to be about 3°C. Ground temperature alternated with seasonal air temperature variation. Permafrost base raised in thawing season, and lowered in freezing season. Extrazonal permafrost had been degrading but existed until at least 1989. Finally it melted out by the fall of 1990. It is likely that advective heat flow, which is related to wind blowing holes, played roles in aggradation and preservation of frozen ground.