北横岳

The Yokodake lava dome, with eight small craters, 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 most recent eruption took place about 800 years ago, when ash emission accompanied emplacement of a small lava flow. 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.