黒部峡谷・志合谷のなだれ I : 志合谷なだれの予備調査

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A preliminary observation on the avalanche of the Shiai-dani valley, Kurobe Canyon, North Japan Alps, Honshu (Figs. 1 and 2), was carried out during the winter of 1971-1972. The principal subject of the preliminary observation was to figure out the magnitude of the avalanche of the Shiai-dani valley. Ten sets of penetrometer (Figs. 4 and 5) were installed around the observation site (Fig. 7) : 6 sets on the concrete wall and 4 sets on two frameworks of iron beams with an H shape in the cross section (Fig. 6). (1) From the monthly routine observations of snow accumulation, it was presumed that the amount of snow accumulation through the winter of 1971-1972 in the Kurobe Canyon was less than a half of the average. (2) During the period from February 20 to March 15, 1972, an avalanche assaulted the observation site of the Shiai-dani valley. As the result, upper beams of the iron frameworks were bent to the downhill side of the valley (Figs. 8, 9 and 13) : the directions of the bend of the both beams were almost parallel and coincided with that of the avalanche of 1938 which killed 82 workmen : the airection of the avalanche was given by arrow marks in Figs. 7 and 10. (3) The intensity of the avalanche loading in t/m2 calculated simply from the record of the penetrometers as the static loading is given in Table 1, without particular calibration. i) Fig. 7 gives the distribution of the intensity of the avalanche loading in t/m2 around the observation site. The values in the right half area of the site appeared larger than those in the left half area by twice or more. It could be presumed that the main body of the avalanche ran through the right half of the site or a little more toward the valley side of it. The largest value of the intensity of the avalanche loading (66.9 t/m2) was recorded at the point Q-S, while the smallest value (0.7 t/m2) at the point B which was at a distance of only several meters from the point Q-S, laterally to the avalanche. Moreover, the distribution of the intensity of the avalanche loading over the observation site showed some complicated features, which might have been resulted from the strong effect of the minute surface topography of this area. ii) The intensity of the avalanche loading at point S appeared larger than that at point R, of both P and Q. A supporting effect of the supporting legs of the framework could be reflected on this result; if so, the value at the point S would be closer to the real value than that at the point R. (4) The Shiai-dani valley is a very steep and deep valley with the mean inclination of 30°; it has a total length of 2 km, and a depth of about 40 m in the vicinity of the observation site even in the snow season. At a point about 100 m upstream from the observation site, the valley curves sharply to the right making an angle of about 70°. According to such topographic conditions, it was presumed that the avalanche falling down along the Shiai-dani valley collided against the steep face of the right bank side of the valley at the curve (X mark in Fig. 10), then directly assaulted the observation site without running in the valley.
社団法人日本雪氷学会の論文

黒部峡谷・志合谷のなだれ I : 志合谷なだれの予備調査

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