Full glossary

Zao (or Zaozan, Zaosan) volcano is the most active volcano of northern Honshu and consists of a group of stratovolcanoes forming the crest of the divide between the Pacific Ocean and the Japan Sea.
The older parts of the complex are Ryuzan volcano in the west and Byobu and Fubo volcanoes forming the southern group. Zao volcano proper (Chuo-Zao) is the youngest edifice and forms the central part of the group. One of its youngest summit lava domes is Goshiki-dake, which contains the active Okama crater, the source of most of the frequent historical eruptions recorded since the 8th century AD.
Okama crater contains a colorful, strongly acidic crater lake (pH 1.3).

The Pleistocene Ryuzan volcano forms the western Zao group (Nishi-Zao), and Byobu and Fubo volcanoes form the southern Zao group (Minami-Zao). The complex was constructed over granitic basement rocks as high as 1500 m and thus has a relatively small volume. The 7 cu km Zao volcano proper forms the central ao group (Chuo-Zao), a volcanic complex topped by several lava domes and the Goshiki-dake tuff cone, aligned along a NW-SE trend. Several episodes of edifice collapse produced debris avalanches during the Pleistocene.