Strong summit fumarolic activity has caused heavy sulfurous alteration of rocks there. Geothermal wells were drilled in the volcanic field, including Akita-Yakeyama.
Heavy snows cover the volcano in winter.
Click on the index link or scroll down to read the reports. All information contained in these reports is preliminary and subject to change. The following is based on a report by Shintaro Hayashi. Although the landslide began moving a few days before 11 May, the sliding accelerated 20 minutes before the explosion. The explosion, heard as far as 1.4 km away, triggered a mudflow along the Akagawa River and eventually developed into a debris flow downstream.