KVERT reported that seismic activity at Shiveluch was above background levels during 17-24 April. Based on interpretations of seismic data, ash plumes likely rose to altitudes of 4.5-5.3 km (14,800-17,400 ft) a.s.l. Analysis of satellite imagery revealed a daily thermal anomaly on the lava dome. According to observers, fumaroles were active during 16-22 and 22 April. A hot avalanche produced an ash plume that rose to an altitude of 4 km (13,100 ft) a.s.l. on 22 April.

On 25 April, increased seismicity indicated that an ash plume rose to an altitude of 7.5 km (24,600 ft) a.s.l. On 26 April, seismicity remained at high levels; continuous spasmodic tremor and a series of weak shallow earthquakes occurred. An ash explosion from the lava dome was seen on video camera. Ash emitted from a large fissure on the S flank of the lava dome produced plumes that rose to an altitude of 4 km (13,100 ft) a.s.l. and drifted ESE. The Level of Concern Color Code was raised to Red. The next day, seismicity decreased slightly but remained elevated and gas-and-steam emissions with some ash content emanated from the fissure. Based on video camera views and analysis of satellite imagery, plumes rose to altitudes of 3.5-5 km (11,500-16,400 ft) a.s.l. during 27-28 April and drifted 250 km NE. On 28 April, pyroclastic flows originated from areas near the lava dome. The Level of Concern Color Code was lowered to Orange.

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)