Report on Asamayama (Japan) — April 1995
Bulletin of the Global Volcanism Network, vol. 20, no. 4 (April 1995)
Managing Editor: Richard Wunderman.
Asamayama (Japan) First month with over 1,000 earthquakes since 1991
Please cite this report as:
Global Volcanism Program, 1995. Report on Asamayama (Japan). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 20:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199504-283110.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
Last reported on in 1991 (BGVN 16:04), but one of Japan's most active volcanoes, Asama had an increase in seismicity during mid-April. On 17 April the seismic system at station B, 2 km S of the summit, recorded 107 earthquakes. After that, the daily number of earthquakes dropped to between about 10 and 80. The total number of April earthquakes at station B was 1031; the last month with over 1,000 detected earthquakes was April 1991 (1,051).
Asama has had over 100 explosive eruptions since ~350 AD. The vast majority of these eruptions have been assigned Volcanic Explosivity Index (VEI) values of 2-3, but several had VEI values of 4 or 5.
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: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.