Although the volcano was often obscured by clouds, gas-and-steam plumes were frequently observed between mid-July and mid-October. On 14 July, a plume rose from two vents to a height of 50 m. Gas-and-steam plumes were seen on 21 and 25-26 July rising as high as 200 m above the summit. Similar plumes occurring on 1, 5-6, 21, and 27-29 August had variable heights of 50-600 m.

Gas and steam plumes were seen on 6, 8-12, 15-22, 25, 27-28, and 30 September, and 8-9 October, usually rising 50-100 m with some reaching 1,000 m. On 7 September an ash-rich plume rose at least 150-300 m above the summit crater. An ash-and-gas plume on 26 September rose 300 m and extended 8 km SE. Another plume of gas and steam on 27-28 September rose 300-600 m and extended 10 km ESE.

During most of July seismicity remained at background level, with the exception of an hour or more of intense activity on the 23rd. From 28 July through 29 September seismicity was above background level; seismicity was concentrated near the summit crater and at depths of 25-30 km between 25 August and 22 September. Volcanic earthquakes registered inside the crater on 1-4, 7, and 20 August. During 30 September-12 October seismicity remained at about background level.

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: 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.