Report on Asamayama (Japan) — May 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 5 (May 1981)
Managing Editor: Lindsay McClelland.
Asamayama (Japan) Increased seismicity but no eruption
Please cite this report as:
Global Volcanism Program, 1981. Report on Asamayama (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198105-283110.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
After a substantial increase in seismicity during the second half of 1980, the number of recorded earthquakes declined December-February. A sudden increase from fewer than 400 in February to nearly 1,000 in mid-March was not accompanied by any observed eruption or increase in steam ejection. By the end of March, seismicity had declined to the usual level of fewer than 500 recorded earthquakes per month.
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.