北横岳

Yokodake lava dome, capped by eight small craters, has been active into the Holocene. The most recent eruption took place about 800 years ago, when ash emission accompanied emplacement of a small lava flow. Yokodake is at the northern edge of the Kita-Yatsugatake (North Yatsugatake) group of stratovolcanoes and lava domes at the NW end of the NNW-SSE-trending Yatsugatake volcanic massif. The basaltic-to-dacitic Kita Yatsugatake group also contains the Tateshinayama, Shimagareyama, Chausuyama and Futagomine volcanoes. Tateshinayama is sometimes known as Suwa Fuji because of its conical profile. A large lava flow forms the Tateshina-kogen plateau south of Tateshinayama and Yokodake. A debris avalanche from edifice collapse in 888 CE created Matsubara Lake on the east side of the massif.