During mid-September 2002 through February 2003 at Shiveluch, a lava dome continued to grow in the active crater. Short-lived explosions generally sent gas-steam plumes tens of meters to ~3 km above the dome. Seismicity remained above background levels. Earthquakes with magnitudes of ~2-2.7, as well as many smaller ones, occurred at depths of 0-6 km (table 5). Thermal anomalies were visible on satellite imagery (table 6). Intermittent spasmodic tremor with amplitudes of 0.3-1.3 x 10⁶ mps occurred throughout the report period.

Table 5. Earthquakes, explosions, and plumes at Shiveluch during 26 September 2002 through February 2003. Courtesy KVERT.

Table 6. Plumes at Shiveluch visible on satellite imagery during October 2002 through February 2003. Courtesy KVERT.

Incandescence was observed at the lava dome on 6 October. On 11 November, seismic data indicated possible hot avalanches sending clouds up to 5.5 km above the dome.

During late November and early December, gas-and-steam plumes extended >10 km to the E and W. On 19 December, short-lived explosions at 1238 and 1514 sent gas-ash plumes to ~5.5 km and 5.0 km altitude, respectively. In the first case, pyroclastic flows moved to the SE; in the second, to the S, inside the Baidarnaya river. The runout of both pyroclastic flows was 3 km.

On 28 December 2002, a small amount of light-gray ash was observed on the surface of snow. During early January 2003, plumes extended >5-10 km to the W and NW. During late February, plumes extended 10-40 km to the SW, S, and SE. Ash was noted in plumes on 24 October, 1, 11, 15, 19, and 20 November, 1, 19, and 24 December, 4 and 25 January, and 15, 17, 25, and 26 February. The Concern Color Code remained at Yellow.

Geological Summary. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; 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 and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.