An intense eruption at Klyuchevskoy began on 31 October, prompting KVERT to raise the Aviation Color Code to Red (the highest level on a four-color scale). Ash plumes rose as high as 14 km (45,900 ft) a.s.l. and drifted as far as 2,255 km ESE during 31 October-1 November. Lava fountains rose as high has 1 km above the summit and fed lava flows that descended the Apakhonchichsky, Krestovsky, and Kozyrevsky drainages on the SE, S, and W flanks. According to Kamchatka Volcanological Station observers pyroclastic flows descended the flanks. Lahars descended the Studenoy River, blocking the Kozyrevsk-Petropavlovsk federal highway, and descended the Krutenkaya River, blocking the road E of Klyuchi. According to news articles the ash plumes caused some flight cancellations and disruptions in the Aleutians, British Columbia, and along flight paths connecting the Unites States to Japan and South Korea.

Activity began to wane at around 2300 on 1 November and by 2000 on 2 November ash plumes were rising only as high as 6.5 km (21,300 ft) a.s.l. and drifting NNE. The Aviation Color Code was lowered to Orange. The main plume from the most intense phase of the eruption had drifted more than 3,000 km E and SE and contained about 0.1 teragram (100,000 tonnes) of sulfur dioxide based on satellite data. Eruptive activity at the summit continued during 3-4 November, producing ash plumes that rose as high as 5.5 km (18,000 ft) a.s.l. and drifted 125 km ENE. The eruption had ceased by 5 November. Collapses of material and phreatic explosions from hot lava interacting with ice and snow along the Apakhonchichsky drainage generated ash plumes that rose 5.5-8.2 km (18,000-26,900 ft) a.s.l. and drifted almost 260 km E and ENE during 3 and 5-6 November.

Geological Summary. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Sources: Kamchatkan Volcanic Eruption Response Team (KVERT), Kamchatka Volcanological Station, Simon Carn, NewsBreak, Unalaska Community Broadcasting, CHEK Media