During April through mid-June 2002, mild eruptive activity continued at Shiveluch. A lava dome continued to grow in the active crater, gas-and-steam and ash-and-gas emissions occurred, and seismicity remained above background levels. Plumes reached up to 3 km above the lava dome (table 1). Earthquakes reached magnitudes up to 2.4 at depths of 0-10 km. Many other local shallow seismic signals occurred that possibly indicated weak gas-ash explosions and avalanches. Episodes of weak spasmodic volcanic tremor were also registered. Thermal anomalies were visible on AVHRR satellite imagery throughout the report period (table 2). No ash was detected in any image.

Table 1. Plumes reported at Shiveluch during 30 March through 14 June 2002. Courtesy KVERT.

Table 2. Thermal anomalies visible in AVHRR satellite imagery at Shiveluch during 30 March through 13 June. On some days, clouds obscured the view. Courtesy KVERT.

At 1238 on 20 April a 15-minute-long series of shallow events was registered, and at 1240 an increase in eruptive activity was noticed from Klyuchi town (46 km S). Ash clouds rose 800 m along the entire dome. At the same time, a pilot reported an ash cloud 600 m wide and 800 m high above the dome. The character of the ash cloud, as well as photos and visual observations from Klyuchi town suggested that a rockfall had occurred at the dome.

Continuous volcanic tremor was recorded beginning on 3 May. On 5 May a short-lived eruption at 0945 produced an ash-and-gas plume that rose 1.5 km above the lava dome and was accompanied by a 4-minute-long shallow seismic event. At 0050 on 14 May incandescence was observed at the dome summit from Klyuchi town. During the afternoons of 13, 14, and 15 May the nearest seismic station registered high-frequency seismic signals for 14, 11, and 7 hours, respectively. KVERT suggested that the signals were caused by intense snow thawing and running water near the station, masking the volcanic seismicity.

At 2100 on 17 May a gas-and-steam plume containing a small amount of ash rose 800 m above the dome and extended 10 km to the SE; and at 2320 incandescence at the dome summit was observed from Klyuchi town. At 1707 on 21 May a short-lived explosive eruption sent an ash-gas plume to heights of 800 m above the dome. An accompanying 5-minute-long shallow seismic event was registered.

At 1530 on 31 May a large earthquake (ML 3.1) occurred. At 1616 on 1 June eruptive activity increased. Short-lived explosive eruptions sent an ash-gas plume to heights of 3.0 km above the dome, visible from Klyuchi town at 1616 and 1628. Two ~3-minute-long shallow seismic events were registered at 1615 and 1626. During the week, several short-lived explosive eruptions per day sent ash-gas plumes to heights of 700-1000 m above the dome. On 1 and 2 June two 11- and 100-minute-long episodes of strong high-frequency volcanic tremor were registered. The Concern Color Code was increased from Yellow ("volcano is restless") to Orange ("volcano is in eruption or eruption may occur at any time").

Shallow seismic events 4-5 minutes long registered during early June, and there were 1-3 short-lived explosive eruptions per day that probably sent ash-gas plumes to heights of ~1.0 km above the dome. Seismic data did not reveal any strong explosions. As of 14 June the Concern Color Code was returned to 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: 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 (URL: http://www.avo.alaska.edu/), and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.