Seismicity was a little above background levels for most of September. Small earthquakes were registered at a depth of 20-30 km beneath the volcano. Seismic activity returned to normal background levels during late September, October, and the first ten days of November. During this period, fumarolic plumes were commonly observed and extended as high as 1,000 m above the crater.

During late November seismic activity increased to above background levels with some tremor. On 13 November two swarms of shallow earthquakes were registered. At 1200 on 14 November, eruptive activity began. Surface observers estimated that gas-and-ash clouds rose to an altitude of 6,700 m and drifted WSW for 20 km. On 15 November explosions sent gas and ash to 600 m above the crater. A gas-and-ash plume extended to the ENE for ~15 km. On 16-17 November gas-and-ash explosions 400-600 m above the crater were observed with a plume rising 2-2.5 km above the crater and extending 30 km NE. During 18-23 November gas-and-steam plumes reached 150-200 m above the crater with a plume extending SE-NE for 10-20 km. During 25 November-1 December, observers in the vicinity could hear discrete explosions in the crater. On 28 November a gas-and-steam plume rose to 2,000 m above the volcano.

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: Tom Miller, Alaska Volcano Observatory (AVO), 4200 University Drive, Anchorage, AK 99508-4667, USA; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; NOAA/NESDIS Satellite Analysis Branch (SAB), Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.