Last discussed through May 2002 (BGVN 27:05), Shiveluch went on to display mostly mild eruptive activity, punctuated by occasional larger outbursts, during the interval from mid-June through early October 2002. During this reporting period, a lava dome continued to grow in the active crater, both ash-bearing and dominantly gas emissions occurred, and seismicity remained above background levels. Plumes reached up to 7 km above the lava dome (table 3). Earthquakes reached up to M 2.7 at depths of 0-10 km. Other local shallow seismic signals occurred that indicated possible weak gas-and-ash explosions and avalanches. Episodes of weak spasmodic tremor were registered. Thermal anomalies were visible on AVHRR satellite imagery throughout the report period (table 4) but no ash was detected in any image.

Table 3. Plumes reported at Shiveluch during 14 June-11 October 2002. All visual observations and recordings were made from Klyuchi town. Cloudy weather prevented observations on some days. Courtesy KVERT.

Table 4. Thermal anomalies recognized in AVHRR satellite imagery at Shiveluch during 14 June-11 October 2002. On some days, clouds obscured the view or there were no passes over the volcano. Unless noted, all images came from the AVHRR satellite. Courtesy KVERT.

The Level of Concern Code was Yellow ("volcano is restless") throughout the reporting period, except for a few days starting 30 July and again early in August when Code Orange ("volcano is in eruption or eruption may occur at any time") was declared.

Summary of recent activity. Except when the summit was obscured by clouds, ash-and-gas or gas-and-steam plumes were seen visually almost daily (table 3). These plumes, frequently accompanied by short-lived explosions and avalanches, typically rose 1-3 km above the summit with occasional plumes rising as high as 7-10 km.

Similarly, satellite imagery (principally AVHRR) reported significant thermal anomalies on an almost daily basis with an extent of several (1-6) pixels, reaching maximum, band-3 temperatures of 20-49°C and frequently associated with steam or aerosol plumes, some extending over 100 km from the volcano.

From mid-June to late-July, numerous earthquakes were recorded, typically M 1.7 to 2.4 and several reaching M 2.7. At 2000 on 29 July, four earthquakes (M 2.1-2.3) occurred and the intensity of volcanic tremor increased noticeably in comparison with the previous days. The following day (30 July), the Level of Concern was raised from Yellow to Orange, but it returned to Yellow when the tremor amplitude decreased over the following two days. However, the activity level increased again during subsequent days and the level was raised again to Orange.

During 12-16 August, about 10 earthquakes of magnitude 1.7-2.4 occurred. Along with smaller earthquakes and many other local seismic signals, these probably indicated ash and gas explosions (at a rate of 1-3 a day, to heights of 1500-2500 m above the dome). However, the Level of Concern was returned to Yellow by the end of the week.

Through the remainder of the period, many earthquakes up to M 2.7 occurred, frequent gas-and-steam plumes rose as high as 5 km above the dome, and thermal anomalies of 6-8 pixels were observed as were gas/steam plumes that extended 80-120 km. On 25 September, continuous spasmodic tremor prevailed for 27 minutes.

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: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller and Dave Schneider, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, 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 (URL: http://www.avo.alaska.edu/).