Observations and simulations of the formation of the faceted snow crystalsin the weak-layer of the 1998 Niseko Haru no Taki avalanche

On January 28, 1998, an avalanche accident occurred near the Japanese ski r esort Niseko Alpen in Hokkaido. The following morning, a snow-pit was dug t hrough the fracture line and the snow cover analysed. There was a weak laye r of faceted crystals at a depth of 1 m and it was this weak layer that bec ame the slide plane. Meteorological and snow-pit data from a nearby (1 km) site are used with the Crocus model to explain the formation of the faceted crystals as follows. A period of slow surface warming followed by rapid co oling created a large temperature gradient in the layer near the surface of the snow cover which formed a thin layer of faceted crystals near the surf ace. The large gradient remained as the layer became buried and the faceted crystals survived in the snow cover for 9 days until increasing load from snow accumulation led to failure and the avalanche occurred. (C) 2000 Elsev ier Science B.V. All rights reserved.