Elevated seismicity persisted through February and March. Earthquake hypocenters were concentrated at levels near the summit crater and at depths of 25-30 km. Visual observations were hindered by bad weather on many days. Because of increases in activity, the Level of Concern Color Code was changed to Yellow from Green and back three times during the reporting period.

Deeper earthquakes increased toward the end of 1-7 February, and fumarolic plumes rose several hundred meters above the crater during this week. On 5 February a gas explosion sent a plume 2,500 m above the crater. Earthquakes at both shallow and deeper depths continued through 25 February, as did the fumarolic plumes.

Fumarolic or steam plumes were observed during most of the period 15-30 March rising hundreds of meters above the summit before being blown about 5 km. At 1422 on 17 March satellite images showed a steam plume extending 40 km NE. On 20 March separate gas and steam explosions occurring at a rate of 2-3 per hour rose 500 m above the crater. A 17-minute series of earthquakes and tremor was recorded on 3 March and low-amplitude tremor began to be recorded again on 12 March. Between 1918 and 2137 on 20 March a series of near-surface M <1.6 earthquakes occurred.

Geological Summary. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

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.