Suwanosejima

Geography & Climate

Suwanosejima is located in Japan, within the Ryukyu Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 29.64° N, 129.71° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. With a summit elevation of 796 meters above sea level, Suwanosejima 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

Suwanosejima 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 Suwanosejima, 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

Suwanosejima has 20 recorded eruptions in the geological database, spanning from 1915 CE to 2004 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 2000 CE, reaching VEI 3 on the Volcanic Explosivity Index. With an average interval of roughly 4 years between eruptions over a span of 89 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. With eruptive activity as recently as 2004 CE, Suwanosejima remains an actively monitored volcano.

Significance

With a maximum recorded VEI of 3, Suwanosejima 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, Suwanosejima is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. One of Japan's most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits covered residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed, forming a large debris avalanche and creating an open collapse scarp extending to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

— Smithsonian Institution, Global Volcanism Program