During 7-27 December seismicity under the volcano was generally at background. Hypocenters concentrated both at shallow depths near the summit crater and at depths of 25-30 km. On 7 December a fumarolic plume rose 500 m above the crater and extended >10 km E. During 8-11 December a plume rose 50 m above the crater before moving 2-3 km SE and E. On 21 December the plume rose 100 m above the crater, extending 10 km NW. On most other days during December, the volcano was obscured by clouds.

Beginning at 2352 on 23 December a series of shallow earthquakes with magnitudes smaller than M 2 began to be recorded beneath the volcano and at distances of >100 km. At 0400 on 24 December the activity abruptly decreased, although remaining still slightly above background until 1000 that day. Satellite images obtained during and after this anomaly did not show large areas of airborne ash. The level of concern color code was increased to yellow.

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: Vladimir Kirianov, 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.