This report covers 20 October-15 November 2000. At the end of October, the hazard status was Yellow. During 22-23 October, seismographs recorded weak continuous tremor and small shallow earthquakes. On 24, 26, and 28 October, shallow seismic events indicated possible explosions. Plume height was estimated at 700-1,200 m above the summit; heights were inferred by correlating previous observed ash-clouds with magnitudes of associated explosions. On 25 October, a gas-and-steam plume rose 200 m above the summit dome. A gas-and-steam plume on the 29th rose 700 m and extended more than 5 km E and NW.

During the first week of November, gas-and-steam plumes ranged from 100 to 300 m above the summit, with one on the 7th rising 1.5 km. Seismicity was at background levels during 10-16 November, although a gas-and-steam plume rose 600 m on 16 November. The hazard status was downgraded to Green the following day. Late on 20 November, however, frequent shallow seismic events suggested that gas-and-ash explosions rose to heights of 3.2 km. Gas-and-steam plumes on 19, 20, 21, and 23 November to respective heights of ~2 km, 1 km, 350 m, and 350 m. By the end of November, little seismicity was registered; only three deep M < 1 earthquakes were recorded. On 24 November, a gas-and-steam plume rose 400 m above the dome and drifted 5 km to the E. At 0935 on 27 November, seismographs detected a strong shallow seismic event.

Shiveluch's hazard status was elevated to Yellow on 1 December. A possible explosion the evening of 6 December was followed by tremor. A similar event the following afternoon produced a cloud estimated from seismic data to have risen 700-1,200 m. Weak seismicity was recorded for most of the second week in December. Possible explosions on 9 and 12 December were again suggested by shallow seismic events. Seismographs recorded tremor for 30 minutes after the 9 December explosion, and for 1 hour after the 12 December event; workers estimated plume heights of 700 m for both. On 13 December a gas-and-steam plume rose 200 m. Shiveluch's extrusive dome and W summit crater wall were observed to be coated with ash, likely from the 12 December explosion.

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.