Report on Hokkaido-Komagatake (Japan) — May 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 5 (May 1996)
Managing Editor: Richard Wunderman.
Hokkaido-Komagatake (Japan) Steaming activity continues
Please cite this report as:
Global Volcanism Program, 1996. Report on Hokkaido-Komagatake (Japan). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 21:5. Smithsonian Institution. https://dx.doi.org/10.5479/si.GVP.BGVN199605-285020.
42.063°N, 140.677°E; summit elev. 1131 m
All times are local (unless otherwise noted)
Activity has declined since the eruptive events of March when two vents opened on and near the S side of Showa 4-nen (1929) crater, and a line of vents extending ~200 m N-S formed on the S part of the crater floor. The height of the gas plume remained at 100-200 m. A volcanic earthquake occurred on 15 May. No volcanic tremor was observed.
Komaga-take sits 30 km N of Hakodate City (population 320,000). The andesitic stratovolcano has a 2-km-wide horseshoe-shaped caldera open to the E. The volcano has generated large pyroclastic eruptions, including major historical eruptions in 1640, 1856, and 1929. In the 1640 eruption, debris from a partial summit collapse entered the sea resulting in a tsunami that killed 700 people. Although the 1929 eruption was one of the largest 20th century eruptions in Japan, it may not have had clear geophysical precursors.
Geologic Background. The truncated Hokkaido-Komagatake volcano on the Oshima Peninsula of southern Hokkaido is one of the most active volcanoes of Japan's northernmost island. The sharp-topped 1131-m-high 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. Much of the andesitic volcano is Pleistocene in age. 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.
Information Contacts: Japan Meteorological Agency (JMA), Volcanological Division, Seismological and Volcanological Department, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.