JMA reported that tremor was detected at Zaozan on 28 and 30 January, and minor inflation at the S part of the volcano was recorded. There were 12 volcanic earthquakes detected on 31 January. JMA raised the Alert level to 2 (on a 5-level scale), noting the increased potential for a small eruption.

Source: Japan Meteorological Agency (JMA)

Geological Summary. The Zaozan (or Zaosan) volcano group consists of a complex cluster of stratovolcanoes in north-central Honshu about 40 km W of Sendai Bay. The Pleistocene Ryuzan volcano forms the western group (Nishi-Zao), and Byobu and Fubo volcanoes form the southern group (Minami-Zao). The Zaozan edifice forms the central group (Chuo-Zao), a complex topped by several lava domes and the Goshikidake tuff cone, aligned NW-SE. Several episodes of edifice collapse produced debris avalanches during the Pleistocene. Goshikidake contains the active Okama crater, filled with a strongly acidic crater lake; it has been the source of most of the frequent eruptions recorded since the 8th century CE.