Hokkaido-Komagatake

Geography & Climate

Hokkaido-Komagatake is located in Japan, within the Northeast Japan Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 42.06° N, 140.68° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,131 meters above sea level, Hokkaido-Komagatake 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

Hokkaido-Komagatake 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 Hokkaido-Komagatake, 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

Hokkaido-Komagatake has 20 recorded eruptions in the geological database, spanning from 1640 CE to 2000 CE. The most powerful recorded event was a paroxysmal eruption with devastating regional consequences in 1640 CE, reaching VEI 5 on the Volcanic Explosivity Index. Notable eruptions include 1942 CE (VEI 3), 1929 CE (VEI 4), 1856 CE (VEI 4). With an average interval of roughly 18 years between eruptions over a span of 360 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 2000 CE, Hokkaido-Komagatake remains an actively monitored volcano.

Significance

With a maximum recorded VEI of 5, Hokkaido-Komagatake has demonstrated the capacity for paroxysmal eruptions comparable to the 1980 eruption of Mount St. Helens. Eruptions of this scale can devastate areas within 20-30 kilometers and produce ash fall that disrupts aviation and agriculture across hundreds of kilometers. 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, Hokkaido-Komagatake is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

Much of the truncated Hokkaido-Komagatake andesitic volcano on the Oshima Peninsula of southern Hokkaido is Pleistocene in age. The sharp-topped summit lies at the western side of a large breached crater that formed as a result of edifice collapse in 1640 CE. Hummocky debris avalanche material occurs at the base of the volcano on three sides. Two late-Pleistocene and two Holocene Plinian eruptions occurred prior to the first historical eruption in 1640, which began a period of more frequent explosive activity. The 1640 eruption, one of the largest in Japan during historical time, deposited ash as far away as central Honshu and produced a debris avalanche that reached the sea. The resulting tsunami caused 700 fatalities. Three Plinian eruptions have occurred since 1640; in 1694, 1856, and 1929.

— Smithsonian Institution, Global Volcanism Program