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Report on Asamayama (Japan) — September 1990


Bulletin of the Global Volcanism Network, vol. 15, no. 9 (September 1990)
Managing Editor: Lindsay McClelland.

Asamayama (Japan) Seismicity and steam emission at high levels

Please cite this report as:

Global Volcanism Program, 1990. Report on Asamayama (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199009-283110



36.406°N, 138.523°E; summit elev. 2568 m

All times are local (unless otherwise noted)

Seismicity fluctuated, but remained at high levels (204 earthquakes during September, up from 104 in August) . . . . Peaks in seismicity occurred in early and late September (55 earthquakes were recorded on the 26th, the most in a single day since activity increased in March), both preceded by periods of low seismicity. The number of volcanic tremor events also increased during late September and the monthly total (26) was increased from August when 13 were recorded. Steam plume heights . . . remained high in September (figure 11).

Figure (see Caption) Figure 11. Monthly mean cloud height at Asama, 1970-90. Arrows at top mark eruptions. Courtesy of JMA.

Geological Summary. 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.