JMA reported that Asama had four minor, brief (under 10-minute duration) eruptions thus far during 2003, the latest on 18 April when an ash cloud rose ~300 m. The first of the previous three occurred on 6 February when an ash cloud rose ~300 m and minor ash fell around the summit. The second took place on 30 March; again an ash cloud rose ~300 m and minor ash fell around the summit. The third took place on 7 April; in this case an ash cloud rose ~200 m. No unusual precursory seismic activity preceded these events. Asama lies in central Japan W of Tokyo, near the site of the 1998 Winter Olympic Games.

Geological Summary. 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 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-Asamayama 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 observed activity 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.

Source: Japan Meteorological Agency (JMA)