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

Abstract

On January 28, 1998, an avalanche accident occurred near the Japanese ski resort Niseko Alpen in Hokkaido. The following morning, a snow-pit was dug through the fracture line and the snow cover analysed. There was a weak layer of faceted crystals at a depth of 1 m and it was this weak layer that became 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 cooling 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 surface. 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.