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Use of Gaz.ex for Japan’s central mountains

Published online by Cambridge University Press:  20 January 2017

Isao Kamiishi
Affiliation:
ARGOS Co. Ltd., Gakkouchou Arai, Japan
Akimichi Iiyoshi
Affiliation:
Tokyo Club Inc., Sanbongishinden Arai, Japan
Norio Hayakawa
Affiliation:
Nagaoka University of Technology, Nagaoka, Niigata 940–21, Japan
Kunio Kawada
Affiliation:
Toyama University, Toyama 930, Japan
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Abstract

Type
Research Article
Copyright
Copyright © International Glaciological Society 1993

Summary

Japan’s central mountains receive a large quantity of snow, due to winter winds blowing across the Sea of Japan. This snow is generally heavy and very wet. In this region, development of large-scale ski areas is increasingly common in recent years, making development of avalanche control an urgently needed technology.

Gaz.ex, an avalanche-blasting device recently developed in France, appears a promising technology for this environment, although it has been used mainly in the area where snow is light and the weather quite cold. Gaz.exes of different capacity have been installed and tested on Mount Ougenashi, Niigata Prefecture of Japan.

The eastern slope of Mount Ougenashi (elevation 1429 m) is being developed as a ski area. On this slope, two Gaz.exes were installed in December 1991 at an elevation of about 1200 m. Numbered A-l and A-2, their capacities are, respectively, 3.0 m3 and 2.6 m3. In normal years the maximum snow depth reaches almost 7 m at this location. Deposited snow quickly turns to compacted or granular snow, with density of 0.3–0.4 g cm−3. Minimum temperatures are −10°C at this location.

More than a dozen test firings of these Gaz.exes in January and February 1992 failed to set off avalanches. Most were done under clear skies and in daytime, when snow surfaces became hard-crusted.

Success was obtained on 27 February 1992, when at A-l an avalanche was released with width of 100 m, flowing down to the valley bottom and then uphill over the other side of the valley to come to a stop 600 m from

Fig. 1. Snow-pit observation at A-l.

the release point. A much narrower avalanche set off by A-2 traveled about 300 m.

A snow-pit observation at the release point of A-l is given in Figure 1, showing a surface layer of 120 cm thickness lying over the bottom layer, with a fragile layer of solid-type depth hoar between. A shear test showed that the snow layer was at the brink of fracture, confirming that the avalanche was released at this fragile layer.

Snow depth temperature and weather conditions prior to the experiment favoured the formation of this fragile layer.

Figure 0

Fig. 1. Snow-pit observation at A-l.