Report on Shikotsu (Japan) — May 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 5 (May 1979)
Managing Editor: David Squires.
Shikotsu (Japan) Seismicity and number of explosions decline
Please cite this report as:
Global Volcanism Program, 1979. Report on Shikotsu (Japan). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 4:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197905-285040.
42.688°N, 141.38°E; summit elev. 1320 m
All times are local (unless otherwise noted)
Eruptive and seismic activity declined substantially in April. Only one [ash eruption] took place in April, on the 13th, causing a small ashfall in the summit area. The monthly number of recorded earthquakes dropped from 223 in March to 70 in April.
Geologic Background. 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.
Information Contacts: JMA, Tokyo.