Based on interpretations of seismic data, a large eruption occurred at Shiveluch from 1825 on 27 February to 0100 on 28 February, leading KVERT to raise the Concern Color Code from Orange to Red (the highest level). Meteorological clouds obscured the volcano during the eruption. A large thermal anomaly visible near the lava dome on satellite imagery at 0456 on 28 February was probably the signal from a large pyroclastic flow on the volcano's SW flank. At this time a 45-km-long ash cloud was visible on satellite imagery trending NW of the volcano. At 0900 on the 28th, ash deposits were noted in the town of Klyuchi, ~46 km from the volcano. Satellite imagery from 1205 on 28 February showed ash deposits W of Shiveluch covering an area of 24,800 square kilometers. Later that day, an ash cloud extending more than 360 km was centered over the western half of Kamchatka. On 1 March the Concern Color Code was reduced to Orange. Prior to the eruption, during 18-26 February, seismicity was above background levels and ash-and-gas plumes were seen on video rising to ~3 km above the lava dome.

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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)