Io-Torishima

Geography & Climate

Io-Torishima is located in Japan, within the Ryukyu Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 27.88° N, 128.22° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. At just 212 meters above sea level, Io-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

Io-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 Io-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 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

Io-Torishima has 9 recorded eruptions in the geological database, spanning from 1664 CE to 1968 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 1959 CE, reaching VEI 2 on the Volcanic Explosivity Index. This eruption frequency indicates a moderately active volcanic system with periodic reawakenings. The most recent eruption in 1968 CE places this volcano within the modern era of volcanological observation.

Significance

With 9 recorded eruptions on file, Io-Torishima has enough documented activity to help scientists identify patterns in its eruptive behavior. Given its recent activity, Io-Torishima is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The 1 x 2.7 km island of Io-Torishima, located north of the largest island of the Ryukyus, Okinawa, is composed of two andesitic volcanoes. Torishima (Bird Island) is a common name for offshore islands in Japan. Kusuku lava dome occupies the center of the inner of two sommas on the SE-most volcano. The summit crater of the NW-most volcano, Iodake, contains a small lake, solfataras, and sulfur deposits that were mined in the past. Historical eruptions dating back to 1664 have consisted of mild-to-moderate explosive activity.

— Smithsonian Institution, Global Volcanism Program