Shikotsu

Geography & Climate

Shikotsu is located in Japan, within the Northeast Japan Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 42.69° N, 141.38° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,320 meters above sea level, Shikotsu is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a caldera, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Shikotsu 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 Shikotsu, 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

Shikotsu has 20 recorded eruptions in the geological database, spanning from 1920 CE to 1981 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 1951 CE, reaching VEI 2 on the Volcanic Explosivity Index. With an average interval of roughly 3 years between eruptions over a span of 61 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. The most recent eruption in 1981 CE places this volcano within the modern era of volcanological observation.

Significance

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, Shikotsu is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The 13 x 15 km Shikotsu caldera, largely filled by the waters of Lake Shikotsu, was formed during one of Hokkaido's largest Quaternary eruptions about 31-34,000 years ago. The small andesitic Tarumaesan stratovolcano was then constructed on its SE rim and has been frequently active in historical time. Pyroclastic-flow deposits from Tarumaesan extend nearly to the Pacific coast. Two other Holocene post-caldera volcanoes, Fuppushidake (adjacent to Tarumaesan) and Eniwadake (on the opposite side of the caldera), occur on a line trending NW from Tarumaesan, and were constructed just inside the caldera rim. Minor eruptions took place from the summit of Eniwadake as late as the 17th century. The summit of Tarumaesan contains a small 1.5-km-wide caldera formed during two of Hokkaido's largest historical eruptions, in 1667 and 1739. Tarumaesan is now capped by a flat-topped summit lava dome that formed in 1909.

— Smithsonian Institution, Global Volcanism Program