Rockfall hazard in the Daisekkei Valley, the northern Japanese Alps, on 11 August 2005
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This paper describes a rockfall event in the Daisekkei Valley of Mount Shirouma-dake (2,932 m), the northern Japanese Alps. The rockfall occurred on a steep cliff comprising well-jointed felsites and produced debris of ≥8,000 m3. Most debris was deposited on an elongated snowpatch located immediately beneath the cliff, and it caused casualties among people who were trekking along a trail on the snowpatch. Additionally, a large rock block slipped 1 km on the snowpatch. The rockfall could have been due to the differential retreat of the rockwall, which contains areas of high- and low-density joints. Seasonal and diurnal freeze–thaw activities and snow avalanches and wash appear to be important factors responsible for the retreat. Although some rock blocks that can collapse further remain on the rockwall, the position of the mountain trail in the Daisekkei Valley is fixed. Fundamental reform of tourism systems for climbers, including education on natural hazards, is required.
KeywordsRockfall Alpine landscape Snowpatch Northern Japanese Alps Japan
We thank the anonymous couple, Hakuba Village Office, Chubu Regional Forest Office of Forest Agency, Hakuba-kan Co. Ltd., the Association for Alpine Accident of the Northern Japanese Alps, Hiroshi Tsuruoka, and Shuji Iwata for their help in the field and the laboratory. This paper has benefited from the constructive comments from Heather Viles.
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