An increase in volcanic tremor at Kliuchevskoi led KVERT to raise the Concern Color Code from Green ("volcano is in quiet, "dormant" state") to Yellow ("volcano is restless") on 31 May. During most of the report week (24-31 May) seismicity was near background levels. Weak shallow earthquakes, other earthquakes ~30 km under the volcano, and episodes of weak spasmodic tremor were registered. On 24 and 27 May gas-and-steam plumes rose 100 m above the crater. Spasmodic volcanic tremor began to increase on 30 May at 0810, declined at 1000, and began to increase again around 2200. Tremor was still recorded on 31 May. No thermal anomalies or plumes were observed on satellite imagery.

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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)