Shiretoko-Iozan

Geography & Climate

Shiretoko-Iozan is located in Japan, within the Kuril Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 44.13° N, 145.16° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,562 meters above sea level, Shiretoko-Iozan 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

Shiretoko-Iozan 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 Shiretoko-Iozan, 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

Shiretoko-Iozan has 7 recorded eruptions in the geological database, spanning from 850 CE to 1935 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 1889 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 1935 CE places this volcano within the modern era of volcanological observation.

Significance

With 7 recorded eruptions on file, Shiretoko-Iozan has enough documented activity to help scientists identify patterns in its eruptive behavior.

GVP Reference Summary

Shiretoko-Iozan, one of many Japanese "sulfur mountains," is noted for the extrusion of molten sulfur during eruptions in 1889 and 1936. Located at the NE tip of Hokkaido on the Shiretoko Peninsula, the andesitic volcano contains two large craters at the summit that are breached to the NW. The southern crater contains a small flat-topped lava dome. The main cone, Nakadake, was constructed NW of the headwalls of the two breached craters. Historical eruptions have originated from the southernmost of three explosion craters along a NNE-SSW line on the NW flank of the main cone.

— Smithsonian Institution, Global Volcanism Program