The intermittent explosions and elevated seismicity reported in BGVN 28:11 continued through December 2003. The Tokyo Volcanic Ash Advisory Center (VAAC) reported, for the period 28 November-5 December, that intermittent explosive eruptions emitted ash up to ~ 3.5 km altitude. The Kamchatkan Volcanic Eruption Response Team (KVERT) reported on 12 December 2003 that intermittent explosive eruptive activity at Karymsky was continuing, with occasional explosions sending ash up to 3.5 km above the volcano and local ashfall possible. Seismicity was above background levels, with 200-250 shallow long-period events per day during the previous week and possible ash-gas explosions rising up to 1-1.5 km above the volcano. Seismic data showed, at 0745 on December 5, a possible ash-gas explosion up to 4 km. Satellite data from 5-10 December showed a 1- to 5-pixel thermal anomaly over the volcano.

KVERT reported similar conditions for the week ending 19 December, with ash to 1-2.5 km above the crater and 160-240 events per day. On 16 December, they reported possible ash plumes up to 3 km above the crater and 1- to 5-pixel thermal anomalies on 11-17 December. These conditions continued during the week ending 26 December, with seismic events fluctuating at 40-200 per day and ash-and-gas plumes rising 1-2 km over the volcano. The number of earthquakes decreased during 18-20 December and increased during 21-24 December, with probable ash explosions to 3.5 km on 21 December.

At 0359 on 23 December and 1605 on 24 December possible explosions with pyroclastic flows were recorded. A 1- to 3-pixel thermal anomaly was observed by satellite on 21-22 and 24-25 December. For the week ending 2 January 2004, local shallow earthquakes took place 200-270 times per day with possible ash-gas explosions to 2-3.5 km. Possible explosions accompanied by pyroclastic flow were recorded on 25, 29, and 31 December; a 1- to 4-pixel thermal anomaly was also observed. On 29 December a very narrow gas-steam plume extended 97 km SE. The color code alert remained at orange during the month.

Geological Summary. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA); Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.