Akagisan

Geography & Climate

Akagisan is located in Japan, within the Northeast Japan Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 36.56° N, 139.19° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,828 meters above sea level, Akagisan is a moderately sized peak that remains accessible to hikers and researchers for much of the year. 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

Akagisan 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 Akagisan, 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

Akagisan has 2 recorded eruptions in the geological database, spanning from 1251 CE to 1938 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1251 CE, reaching VEI 3 on the Volcanic Explosivity Index. These eruptions span roughly 687 years of volcanic history. The most recent eruption in 1938 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Akagisan has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel.

GVP Reference Summary

The broad, low dominantly andesitic Akagisan volcano rises above the northern end of the Kanto Plain. It contains an elliptical, 3 x 4 km summit caldera with post-caldera lava domes arranged along a NW-SE line. Lake Ono is located at the NE end of the caldera. An older stratovolcano was partially destroyed by edifice collapse, producing a debris-avalanche deposit along the south flank. A series of large plinian eruptions accompanied growth of a second stratovolcano during the Pleistocene. Construction of the central cone in the late-Pleistocene summit caldera began following the last of the plinian eruptions about 31,000 years ago. During historical time unusual activity was recorded on several occasions during the 9th century, but reported eruptions in 1251 and 1938 are considered uncertain.

— Smithsonian Institution, Global Volcanism Program