Report on Asamayama (Japan) — July 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 7 (July 1990)
Managing Editor: Lindsay McClelland.
Asamayama (Japan) Small ash eruptions; continued high seismicity
Please cite this report as:
Global Volcanism Program, 1990. Report on Asamayama (Japan). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 15:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199007-283110.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
Small ash eruptions occurred on 20 July from around 0440 to 0700. Slight ashfall was recognized as far as 8 km E from the volcano. No damage was caused and no sounds were heard but seismometers recorded explosion shocks at 0437, 0438, and 0440. The ash plume, photographed by a video camera, was about 1,000 m high.
Seismicity remained at a high level as of 6 August. A seismic station 3.8 km SSE of the volcano recorded 166 earthquakes in July, only a small increase from the June total of 144. Most epicenters were located under the summit. Steam plume heights have increased several hundred meters since March.
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.