The volcano was frequently obscured by clouds during August-December 1999, but small fumarolic gas-and-steam plumes rising 50-200 m were often observed during clear weather. Higher fumarolic plumes were seen on three days in late November-early December. Four short explosions generated ash-bearing plumes during August-December that were confirmed visually. As many as five additional dome explosions were identified seismically.

On 11 and 13-14 August, fumarolic plumes rose 50-200 m above the crater. On 15 August a 5-minute ash explosion sent a plume to 800 m above the crater. On 17 and 23 August, fumarolic plumes rose 200-600 m; on the 30th a similar plume rose 1,200 m. On 4-5, 12, and 23-25 September, fumarolic plumes rose 50-200 m, extending 5 km E or SE. Similar plumes were seen on 7, 11, 23, and 25-26 October. On the morning of 27 October a short-lived ash explosion was observed, with an accompanying 20-minute burst of seismic activity. According to a Japanese satellite image taken about 3.5 hours later, an ash plume extended NE at an altitude of 6,900 m. Overall seismicity remained about at background levels until the end of October.

Seismicity was above background levels in late October through mid-November, when the hazard status was increased to "Yellow." On the morning of 31 October a 20-minute series of shallow earthquakes and tremor may have been associated with explosions on the dome; however, at daylight only a small fumarolic plume was seen. According to visual reports from Klyuchi town, on the late morning of 1 November a short explosive eruption sent an ash plume to an altitude of 5.5-6.0 km and extended S; an accompanying increase in seismicity occurred. On 2 November a fumarolic plume rose 50 m. On 8 and 10 November, three 20-50-minute-long series of shallow earthquakes and tremor were recorded that may have been associated with dome explosions. On 11 November a fumarolic plume rose 200 m.

A 5-minute-long series of shallow earthquakes and tremor was recorded on the morning of 17 November that may have been associated with an explosion on the dome. On 12, 16, 19, and 22 November fumarolic plumes rose 200 m. On the morning of 24 November a gas-and-ash plume rose 3 km above the crater. Plumes rising 1-2 km above the crater were also observed on the evening of 27 November and the afternoon of 2 December. All three of these larger plumes disappeared within one hour. Smaller fumarolic plumes, to 50-200 m above the crater, were seen again on 26 and 29-30 November, and 1-2, 10, 17, and 20-21 December. On the morning of 27 December a possible gas-and-ash plume was registered.

Geological Summary. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.