Report on Shikotsu (Japan) — February 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 2 (February 1979)
Managing Editor: David Squires.
Shikotsu (Japan) Small ash eruptions continue; seismicity increases sharply
Please cite this report as:
Global Volcanism Program, 1979. Report on Shikotsu (Japan). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 4:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197902-285040.
42.688°N, 141.38°E; summit elev. 1320 m
All times are local (unless otherwise noted)
Ash eruptions continued through January. Ash was ejected on 5, 22, 23, and 27 January, darkening snow in the summit area, but no ash reached the foot of the volcano.
Local seismicity increased sharply about 10 January, after several months of relative quiet. An irregular increase in seismic activity has persisted since 1967.
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.