Report on Asamayama (Japan) — 5 February-11 February 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 February-11 February 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Asamayama (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 5 February-11 February 2003. 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 VRC, a photographer noticed two continuous puffs of discolored "smoke" rising from the summit of Asama on 6 February around noon. JMA noted that a puff was recorded on video footage rising 300 m above the summit crater around 1202. A small amount of ash was deposited on snow near the rim of the summit crater. Tremor, related to the emission, started around 1201 and lasted about 40 seconds. Otherwise, seismicity was at background levels and had been for several months. In addition, the temperature of the crater bottom was rather low. The last reported ash eruption at Asama occurred in July 1990.
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.