Report on Asamayama (Japan) — 1 September-7 September 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 1 September-7 September 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, 1 September-7 September 2004. Smithsonian Institution and US Geological Survey.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
According to news reports, the eruption that began at Asama on 1 September subsided the following day. On the 1st, an eruption produced gas and ash that rose to ~ 2 km above the volcano and ash was deposited ~125 miles downwind. JMA reported to news agencies that red glow visible at the volcano in the evening was from a forest fire and not lava flows. About 40 people were evacuated from the neighboring state of Gunma. On the 2nd, tremor had subsided and there was a lull in volcanic activity. The Alert Level remained at 3 (on a scale of 0-5).
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.