The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that the eruption at Klyuchevskoy’s summit crater continued during 4-12 August and was characterized by lava fountains at the summit, two lava flows descending the SW flank, and explosions with ash plumes. The Kamchatka Volcanological Station reported that during a field visit on 4 August observers noted that the SW-flank lava flow may have reached the Bogdanovich glacier. Lava fountains rose as high as 500 m above the crater rim. On 5 August explosions produced ash plumes that rose 7 km (23,000 ft) a.s.l., or 2.2 km above the summit, and drifted as far as 965 km SE. Activity escalated on 6 August with explosions producing ash plumes that rose as high as 9.5 km (31,200 ft) a.s.l., or 4.7 km above the summit, and drifted 141 km ESE. KVERT raised the Aviation Color Code to Red (the highest level on a four-color scale) at 2128. Activity during 7-12 August was slightly variable but remained at high levels. Ash plumes from explosions rose 8-11.5 km (26,200-37,700 ft) a.s.l., or as high as 6.7 km above the summit, and drifted as far as 500 km NW and NE, 1,114 km E, 280 km ESE, and 1,800 km SE.

According to the Kamchatka Volcanological Station a group of tourists and guides visited the volcano for a few days during 7-8 August, when clearer weather allowed for visual observations and photographs of the lava flow. Photographs on 7 August showed that lava overflowed the rim in two areas, separated by a higher rocky area along the crater rim. The two flows merged into one in an area about a third of the way down the flank. Lava fountains rose from the summit crater. The visitors described loud noises through the night, and noted that glow from the lava flow was easily seen from inside closed tents. During the morning of 8 August they saw a large plume of gray ash rising several kilometers high. They walked within 15 m of the lava flow that was advancing along flatter ground, past the base of the edifice, and inspected the distal end of the flow. The flow was covered by gray rocks that rolled down the margins of the flow, appearing as an advancing gray avalanche of blocks with patches of red-hot material inside. During 8-9 August ashfall was reported in Klyuchi (30 km NNE). The group was unable to see the volcano again during most of 9-11 August due to weather conditions, though they continued to hear eruption noises. During a few instances of cleared weather, they noted that the flow was wider and lower, likely melting into the glacier. Activity had decreased by late on 12 August; ash plumes rose as high as 2.2 km above the summit and drifted 140 km SSW. At 2219 the Aviation Color Code was lowered to Orange. Dates and times are provided in Coordinated Universal Time (UTC); specific events are indicated in local time where specified.

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: Kamchatkan Volcanic Eruption Response Team (KVERT), Kamchatka Volcanological Station