KVERT reported that during 15-22 October seismic activity from Kliuchevskoi was above background levels and two lava flows from the summit crater traveled down the SW and W flanks. Satellite imagery analyses showed a large and intense daily thermal anomaly over the volcano and ash plumes that drifted 420 km E and SE. Strombolian activity, observed every day, ejected material 250 m above the crater. Ash plumes rose to an altitude of 7.5 km (24,600 ft) a.s.l. during 20-21 October and to an altitude of 6.5 km (21,300 ft) a.s.l. on the other days during 15-22 October. The Aviation Color Code level remained at Orange.

On 23 October, KVERT reported increased seismicity, characterized by an abrupt change in volcanic tremor, and explosive activity. Ash plumes rose to altitudes of 8-9 km (26,200-29,500 ft) a.s.l. and drifted more than 300 km N. The Aviation Color Code level was raised to Red. The next day the magnitude of tremor decreased and gas-and-steam plumes rose to an altitude of 6.5 km (21,300 ft) a.s.l. Gas-and-steam plumes possibly containing ash drifted SE. The Aviation Color Code level was lowered to Orange. On 25 October, the magnitude of volcanic tremor fluctuated. Ash plumes rose to altitudes of 8-8.5 km (26,200-27,900 ft) a.s.l. and drifted SE. The Aviation Color Code level was again raised to Red. The VAAC reported on 26 October that ash was observed in satellite imagery.

Geological Summary. Klyuchevskoy is the highest and most active volcano on the Kamchatka Peninsula. Since its origin about 6,000 years ago, this symmetrical, basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during approximately the past 3,000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 and 3,600 m elevation. Eruptions recorded since the late 17th century have resulted in frequent changes to the morphology of the 700-m-wide summit crater. These eruptions over the past 400 years have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Sources: Tokyo Volcanic Ash Advisory Center (VAAC), Kamchatkan Volcanic Eruption Response Team (KVERT)