Abstract
large-scale dry slab avalanche occurred at Makunosawa valley in Myoko at 13:48 on
February 17, 2008. The starting zone seemed to be the east-southeast facing slope around 1770m a.s.l.
The point of farthest reach of debris was around 770m a.s.l., and the horizontal runout distance was
about 3000m. The area of the runout zone was about 10ha, and the snow water equivalent of debris
was 400-1500mm (1000mm on average). Accordingly, the mass of the avalanche was estimated at
5-10x10^4t. According to the meteorological data, the weather was clear and the air temperature rose
on February 11. Snowfall began the next morning, and the air temperature dropped rapidly since
the evening of the 12th. The snowfall increased around the same time the air temperature decreased
and the snow depth increased rapidly. When the avalanche was released, the air temperature was
‐6.7℃; the snow depth, which was 252cm on the 12th, increased to 381cm; and the total precipitation
during the same day was 174mm at the meteorological observation site (810m a.s.l.). According to
the numerical snowpack model, faceted crystals were formed on the 13th near the layer, which was
the surface until the 12th. A thick layer of new snow was deposited on the faceted snow layer, and
then the stability index was estimated to decrease to . at the time of the avalanche release.
