Ash explosions and Strombolian activity was reported at Kliuchevskoi through early December 2003 (BGVN 28:11). KVERT reported that unrest continued at Kliuchevskoi over the month of December, with occasional and repeated explosions containing ash, gas and steam rising to 7-8 km altitude, and possible lava flows from the central crater. Seismicity was above background levels over the month. The alert level remained Orange.

Strombolian activity was seen from the town of Klyuchi on 7 December. At 1300 on 6 December an ash explosion up to 1 km above the crater was registered and, on the same day, a 3 km high gas-steam plume was evident. Gas plumes, possibly containing small amounts of ash, rose 100-500 m on 7-16 December, generally extending in various directions and visible to distances of 3-10 km. During this time satellites detected 1- to 9-pixel thermal anomalies. Strombolian activity was again noted from Klyuchi on 12 December.

During the week ending 12 December there were approximately 150 large shallow earthquakes of ML 1.2-2.25 and a large number of weak shallow earthquakes. For example, on 8 December, an earthquake of ML greater than 1.75 was registered at a depth of 5 km under the central crater. On 11 December, 3 earthquakes of ML 1.75-2.0 were registered at a depth of 3-6 km under the central crater. The number of earthquakes was similar during the week ending 19 December.

Tremor occurred often. An index of the tremor's size, reported in terms of relative velocity between the Earth and the seismograph's suspended mass (the ground motion), was 19-23 µm/s on 4-5 December, decreasing to ~ 6.7 µm/s on 9-10 December. On 12 December continuous spasmodic tremor had velocities of 2.5-9.2 µm/s. During the week ending 2 January, tremor had velocities of 2-4 µm/s.

During the week ending 26 December there were 135 large shallow earthquakes of ML 1.9-2.3 and a large number of weak shallow earthquakes were reported. On 19 December, one earthquake at a depth of 11 km and two earthquakes at a depth of 30 km below the central crater (ML less than 2.0) were registered. Continuous spasmodic tremor had velocities of 2.7-5.3 µm/s. Gas-steam plumes were seen rising up to 100 m above the crater on 22-23 December. The volcano was obscured by cloud at other times. A 1-pixel thermal anomaly over the volcano was registered by satellite on 23 December.

During the week ending 2 January 2004, the number of large (ML1.9-2.2) shallow earthquakes dropped to ~ 33, with a large number of weak shallow earthquakes. A 1-pixel thermal anomaly was registered on 26-27 December. On 27-29 December, gas plumes were observed rising up to 50-500 m above the volcano, but the volcano was obscured at other times.

Geological Summary. Klyuchevskoy is the highest and most active volcano on the Kamchatka Peninsula. Since its origin about 6,000 years ago, this symmetrical, basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during approximately the past 3,000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 and 3,600 m elevation. Eruptions recorded since the late 17th century have resulted in frequent changes to the morphology of the 700-m-wide summit crater. These eruptions over the past 400 years have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

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.