JMA reported that at 2208 on 7 August a small phreatic eruption at Asamayama produced an ash plume that rose higher than 1.8 km above the crater rim and drifted N.
Blocks were ejected 200 m from the crater.
The eruption lasted about 20 minutes and was the first since 19 June 2015.
The Alert Level was raised to 3 (on a scale of 1-5).
Ash fell in Tsumagoi Village and Naganohara Town, in the Gunma Prefecture.
White plumes rose as high as 700 m above the crater rim during 8-13 August, and the amount of sulfur dioxide released was 90-200 tons per day.
Source: Japan Meteorological Agency (JMA)