北海道における板状なだれの一特徴

抄録

The block-type debris as Photo. 2 were found at several avalanched sites (Fig. 1) in Hokkaido.
Data obtained are illustrated on Table 1 and Fig. 3.
The results are summarized as follows :
1. The block-type debris are formed when sliding snow are stopped just under nose of fracture lineagainst their obstacles (gentle slope, shrubs, or fixed snow depositions as Fig. 2).
2. The slide surfaces of thin strata are composed of depth hoar or of granular snow in almost cases as Fig. 3.
3. There are much of compact snow at the sites where the hard block-type debris are found (A, B, and E). On the other hand, there are much of granular snow where the nothing is remarkable but the loose block-type traces (C and D).
4. Sliding processes of snow-slab avalanches are discussed with observations of debris forms and crack directions (Photo. 1 to Photo. 6).
5. It is infered that the snow-slab avalanches of the ground avalanche type have occured widely on districts of 1.0 to 1. 5m snow depth in Hokkaido and that they have a tendency to form several slide surfaces in sliding snow concurrently.