Report on Asamayama (Japan) — 25 August-31 August 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 August-31 August 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Asamayama (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 25 August-31 August 2004. Smithsonian Institution and US Geological Survey.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
Based on information from JMA, the Tokyo VAAC reported that an eruption beginning at Asama around 2000 on 1 September produced an ash plume to an unknown height. Ash was not visible on satellite imagery. According to news articles, JMA raised the Alert Level from 2 to 3 and advised people not to visit the volcano. No evacuations were ordered.
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.