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Report on Asamayama (Japan) — 18 September-24 September 2002

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 September-24 September 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, 18 September-24 September 2002. Smithsonian Institution and US Geological Survey.

Volcano Profile |  Weekly Report (18 September-24 September 2002)


Asamayama

Japan

36.406°N, 138.523°E; summit elev. 2568 m

All times are local (unless otherwise noted)


The Asama Volcano Observatory reported that a period of high seismicity began at Asama on 18 September around 0620. Normally 30-59 earthquakes occur daily at the volcano, but on the 18th and 19th, they recorded 243 and 128 volcanic earthquakes, respectively. During this time, a relatively large amount of volcanic gas was emitted from the summit. Seismicity decreased on the 19th, but the temperature of the bottom of the crater lake remained high, as it has since May 2002. No 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.

Sources: Japan Meteorological Agency (JMA), Volcano Research Center-Earthquake Research Institute (University of Tokyo)