Yokodake

Geography & Climate

Yokodake is located in Japan, within the Northeast Japan Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 36.09° N, 138.32° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. At 2,480 meters above sea level, Yokodake rises above the surrounding terrain into montane or subalpine conditions. The elevation creates distinct ecological zones along its flanks, from forested lower slopes to exposed rocky terrain near the summit. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Yokodake sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Japan near Yokodake, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Yokodake has 2 recorded eruptions in the geological database, spanning from 400 BCE to 1200 CE. These eruptions span roughly 1,600 years of volcanic history.

GVP Reference Summary

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.

— Smithsonian Institution, Global Volcanism Program