Monitoring Rockfall and Supranival Debris Movement in the Shirouma Daisekkei Valley, Northern Japanese Alps

Abstract

The Daisekkei Valley (1600-2300 m ASL) is a late Pleistocene glaciated trough in the northern Japanese Alps, and its attractive landscape has enchanted many climbers. Even today, there is a late-lying snowpatch 2 km long at the bottom of the valley in midsummer. Unique natural conditions in and around the Daisekkei Valley (e.g., Quaternary rapid uplift, complex geology, humid climates, sparse vegetation cover) have been responsible for the occurrence of various geomorphic changes that threaten climbers. This study, using an image data-logger capable of capturing a JPG image with a fixed time-interval in the summer of 2007 reveals supranival debris movements, micro-weather conditions and the behavior of climbers in the Daisekkei Valley. Analysis of captured images indicates that the daily numbers of dangerous supranival debris movements gradually decreased from early June to early August and supranival debris movements were caused by rock fragments moving in from valley walls or tributaries to the snowpatch, as well as posture changes of rock fragments on the snow surface with rapid ablation. Besides, image-inspection allows us to consider the relationships among climber traffic, micro-weather, and holiday almanac. Using an image data-logger for monitoring geomorphic changes is considered to be effective for analyzing alpine environments.