7 May 2021
Mount Kekachi: an interesting rock slope failure and rock avalanche in Japan
Yesterday the Toyama Prefectural Police Mountain Guard tweeted a set of images of the aftermath of a large rock slope failure and rock avalanche from the flanks of Mount Kekachi in Toyama Province, Japan:-
— 富山県警察山岳警備隊 (@toyama_sangaku) May 6, 2021
The three images provide a remarkably good view of the events. It is clear that this was a large detachment from a near vertical face:-
The debris has then followed a very steep gully in the form of a rock avalanche. Yoshi Kariya has estimated some statistics for the landslide, which occurred on 6 May 2021. It is about 2 km long with a vertical fall of about 900 metres. The rock avalanche overran by a sabo dam (a check dam across the valley), but stopped a short distance further down the valley.
In the Twitter chain Paisun88 has tweeted some images on the ground showing the rock avalanche material:
— PAISEN88 (@exp88) May 6, 2021
The Google Earth image below shows what I interpret to be the location of the rock slope failure:-
The Google Earth image appears to show that this is an area that had undergone intense undercutting and erosion prior to the collapse. It is notable that the failure has occurred in the spring. Whilst rock slope failures can occur at any time, there is evidence that the snowmelt season is a peak time for these events.