KVERT raised the Concern Color Code at Shiveluch from Orange to Red (the highest level) on 22 September. According to interpretations of seismic data, on the 22nd at 1715 a strong eruption began, with ash plumes reaching ~7.5 km (24,600 ft) a.s.l. [corrected by KVERT to 6.5 km (21,300 ft) a.s.l.] and hot avalanches and pyroclastic flows descending the volcano's flanks. The pyroclastic flows extended 10-15 km. The strongest seismic signal of the eruption occurred on 22 September at 2259. Shallower signals recorded between 22 September at 2330 and 23 September at 1200 were possibly associated with ash emissions that rose to 3.5 km (11,500 ft) a.s.l. An ash plume was visible on satellite imagery at a height of ~3 km (9,850 ft) a.s.l. extending ~20 km SSW. The Concern Color Code was reduced to Orange on 23 September.

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)