Regional characteristics of snowpacks related to avalanches in the central mountains of Japan

摘要

To identify the regional characteristics of mountain snowpacks related to avalanches in the central mountains of Japan, snow-pit observations were carried out over a period of between two and five winters at six study sites in three major mountain ranges: the north, central and south alps. The relationship between snowpack characteristics and meteorological properties was then examined to suggest indicators that could determine the snowpack characteristics in the region using meteorological data. On the basis of the dominant type of persistent weakness found within snowpacks, the study sites were divided into three regions: (1) the mountains on the Sea of Japan side – the persistent weakness was caused mainly by the presence of melt–freeze crust (MFcr) layers; (2) the inland mountains – the persistent weakness was caused mainly by the presence of weak layers consisting of near-surface faceted crystals (FCsf); and (3) the mountains on the Pacific Ocean side – the persistent weakness was caused mainly by the formation of thick weak layers consisting of depth hoar (DH) near the ground. The results also suggest that certain meteorological elements are useful indicators of the tendency of a persistent weakness to form within the snowpack: (1) DH layers: TG (?Cm~(–1)) = |average air temperature|/average snow depth (notable weakness in DH layers is found in areas where the TG exceeds 10?Cm~(–1), but in such areas rainfall prevents the development of DH layers); (2) FCsf layers: FCsf index (?Cm) = average diurnal range of air temperature × snow depth (notable weakness in FCsf layers is found in areas where the FCsf index is ~10?Cm); (3) MFcr layers: MFcr index (daym) = number of days that exceed 0?C×snow depth (notable weakness in MFcr layers is found in areas where the MFcr index exceeds 40 day m).