Izu-Torishima

Geography & Climate

Izu-Torishima is located in Japan, within the Izu Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 30.48° N, 140.30° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. At just 394 meters above sea level, Izu-Torishima is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. 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-Torishima 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-Torishima, 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-Torishima has 7 recorded eruptions in the geological database, spanning from 1871 CE to 2013 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1939 CE, reaching VEI 3 on the Volcanic Explosivity Index. Notable eruptions include 1939 CE (VEI 3), 1902 CE (VEI 3). This eruption frequency indicates a moderately active volcanic system with periodic reawakenings. With eruptive activity as recently as 2013 CE, Izu-Torishima remains an actively monitored volcano.

Significance

With a maximum recorded VEI of 3, Izu-Torishima 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. With 7 recorded eruptions on file, Izu-Torishima has enough documented activity to help scientists identify patterns in its eruptive behavior. Given its recent activity, Izu-Torishima is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The circular, 2.7-km-wide island of Izu-Torishima in the southern Izu Islands is capped by an unvegetated summit cone formed during an eruption in 1939. Fresh lava flows from this eruption form part of the northern coastline of the basaltic-to-dacitic edifice. The volcano is referred to as Izu-Torishima to distinguish it from the several other Japanese island volcanoes called Torishima ("Bird Island"). The main cone is truncated by a 1.5-km-wide caldera that contains two central cones, of which Ioyama is the highest. Historical eruptions have also occurred from flank vents near the north coast and offshore submarine vents. A submarine caldera 6-8 km wide lies immediately to the north.

— Smithsonian Institution, Global Volcanism Program