Izu-Oshima

Geography & Climate

Izu-Oshima is located in Japan, within the Izu Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 34.72° N, 139.39° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. With a summit elevation of 746 meters above sea level, Izu-Oshima 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

Izu-Oshima 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 Izu-Oshima, 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 basalt / picro-basalt, 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

Izu-Oshima has 20 recorded eruptions in the geological database, spanning from 1956 CE to 1990 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1986 CE, reaching VEI 3 on the Volcanic Explosivity Index. With an average interval of roughly 2 years between eruptions over a span of 34 years, this is one of the more frequently active volcanoes in the database. This persistent activity suggests a robust and well-supplied magma system beneath the volcano. The most recent eruption in 1990 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Izu-Oshima 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. Its 20 recorded eruptions make it one of the most prolific volcanoes in our database, reflecting a persistent and well-documented eruptive history that has provided volcanologists with extensive data for understanding eruption patterns and forecasting future activity. Given its recent activity, Izu-Oshima is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

Izu-Oshima volcano in Sagami Bay, east of the Izu Peninsula, is the northernmost of the Izu Islands. The broad, low stratovolcano forms an 11 x 13 km island constructed over the remnants of three older dissected stratovolcanoes. It is capped by a 4-km-wide caldera with a central cone, Miharayama, that has been the site of numerous recorded eruptions datining back to the 7th century CE. More than 40 cones are located within the caldera and along two parallel rift zones trending NNW-SSE. Although it is a dominantly basaltic volcano, strong explosive activity has occurred at intervals of 100-150 years throughout the past few thousand years. A major eruption in 1986 produced spectacular lava fountains up to 1,600 m high and a 16-km-high eruption column; more than 12,000 people were evacuated from the island.

— Smithsonian Institution, Global Volcanism Program