After 2000 on 10 May, tremors of increasing amplitude built up. 11 May. A maximum amplitude was reached at 0732, followed by a hiatus during 0753-0757. Air photos taken on 12 May by Asia Air Survey Co. can be seen on the internet. 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.
The explosion occurred at about noon on 16 August. JMA estimated that the epicenters were just below the summit. Reported on the Volcano Research Center's Current Eruptions in Japan website from JMA reports for 22 and 25 August. A 17 August JMA report detailed the discovery of a new crater 20 m in diameter on the SE rim of Karanuma Crater. The report noted that the new crater no longer emitted an eruption cloud on 17 August.