Report on Asamayama (Japan) — 19 June-25 June 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 19 June-25 June 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Asamayama (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 19 June-25 June 2002. Smithsonian Institution and US Geological Survey.
36.406°N, 138.523°E; summit elev. 2568 m
All times are local (unless otherwise noted)
The number of volcanic earthquakes at Asama began to increase on 22 June around 0100. JMA reported that a total of 210 earthquakes occurred during 0100-0800, with the number of B-type earthquakes peaking around 0300 and A-type earthquakes occurring during 0300-0700. In addition, the temperature of the crater floor had increased since May 2002. According to news reports, crater-floor temperatures were the highest recorded since measurements began in 1994. Plumes rose 700 and 1,000 m above the summit on 2 and 4 June, respectively. On 22 June, access was restricted within 4 km of Asama's summit. After the 22nd, seismicity gradually decreased and by the 24th neither volcanic tremor nor notable changes in ground deformation were recorded.
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.