Report on Shikotsu (Japan) — June 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 6 (June 1979)
Managing Editor: David Squires.
Shikotsu (Japan) Small ash eruption but decline in seismicity persists
Please cite this report as:
Global Volcanism Program, 1979. Report on Shikotsu (Japan) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 4:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197906-285040.
42.688°N, 141.38°E; summit elev. 1320 m
All times are local (unless otherwise noted)
The decline in activity continued through May. A single small ash eruption occurred in May, on the 11th. Ash fell in the summit area but not reach the foot of the volcano. Monthly recorded earthquakes decreased slightly from 70 in April to 66 in May, but the number of tremor events dropped more sharply, from more than 40 to 9. The tremor events, each lasting a few minutes, were thought to be generated by vigorous activity at a vent. The strongest of this activity was visible from the base of the volcano.
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.