Disastor on May 18, 1978

Considerations on the Mechanism of the Slope Failure, Myoko

Abstract

The steep slope of Mt. Akakura, near the Shirataki-Fall hanging in the upper coarse of the Shirotagiri River which flows eastwards from the Myoko Caldera to drain into the Seki River, had failured on May 18, 1978.
Collapsed soils and rocks had made a debris-avalanche and attacked the New Akakura Spa four kilometers downstream.
As the results of investigation on the slope failure, the primary collapse phenomenon occured early in the morning of the day can be subdivided into following three steps; the initial, the main and the continual failures.
These failures are mainly due to the seepage of the melting water of the snow into the debris which was laid on the slope under the unstable conditions.
Moreover, it is undeniable that the slope failure is accelerated by the defenseless forest road constructed across the slope.