Nakanoshima

Geography & Climate

Nakanoshima is located in Japan, within the Ryukyu Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 29.86° N, 129.86° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. With a summit elevation of 979 meters above sea level, Nakanoshima 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

Nakanoshima 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 Nakanoshima, 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

Nakanoshima has 2 recorded eruptions in the geological database, spanning from 1914 CE to 1949 CE. The most powerful recorded event was a gentle, effusive event in 1949 CE, reaching VEI 1 on the Volcanic Explosivity Index. These eruptions span roughly 35 years of volcanic history. The most recent eruption in 1949 CE places this volcano within the modern era of volcanological observation.

GVP Reference Summary

The 9 x 5 km island of Nakanoshima is surrounded by coral reefs. A flat plateau separates the older dissected Sakiwaridake volcano on the south from the active andesitic cone of Ontake, which forms the northern half of the island. Ontake contains a summit crater that is filled with water during the rainy season. Sulfur deposits were mined at a SE-flank solfatara until 1944. Only very minor activity has been reported in historical time. A small mud eruption took place in 1914 at the summit crater, and "smoking" increased in 1949.

— Smithsonian Institution, Global Volcanism Program