Report on Asamayama (Japan) — September 1980
Scientific Event Alert Network Bulletin, vol. 5, no. 9 (September 1980)
Managing Editor: David Squires.
Asamayama (Japan) Seismicity increases
Please cite this report as:
Global Volcanism Program, 1980. Report on Asamayama (Japan) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 5:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198009-283110.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
Seismicity has increased substantially during the past 6 months, reaching the highest monthly total since August 1977 (figure 2). The number of recorded earthquakes peaked in September, declining slightly late in the month. No eruptive activity was observed, but monitoring was enhanced at Asama's JMA observatory.
|Figure 2. Number of seismic events recorded per month at Asama, January 1971-November 1980. The eruptions of February and March 1973 are indicated by arrows at the top. Courtesy of JMA.|
Geologic Background. Asamayama, Honshu's most active volcano, overlooks the resort town of Karuizawa, 140 km NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the horseshoe-shaped remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 BP, and by growth of the Ko-Asama-yama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has an historical record dating back at least to the 11th century CE. Maekake has had several major plinian eruptions, the last two of which occurred in 1108 (Asamayama's largest Holocene eruption) and 1783 CE.
Information Contacts: JMA, Tokyo.