SVERT and KVERT reported increased activity and ash emissions at Sarychev Peak in mid-September. A thermal anomaly had been periodically visible since 7 May 2018, though more recently anomalies were detected during 8 and 11-12 September. Explosions sometimes occurred during 11 and 13-15 September, and ash emissions rose 3-4 km (10,000-13,100 ft) a.s.l. On 14 September ash plumes drifted as far as 120 km. On 14 September KVERT stated that the Aviation Color Code was raised to Orange, though on 17 September SVERT noted that the Aviation Color Code was at Yellow. KVERT reported that explosions at 0910 on 17 September generated ash plumes that rose as high as 4.5 km (14,800 ft) a.s.l. and drifted 21 km NE.

Geological Summary. Sarychev Peak, one of the most active volcanoes of the Kuril Islands, occupies the NW end of Matua Island in the central Kuriles. The andesitic central cone was constructed within a 3-3.5-km-wide caldera, whose rim is exposed only on the SW side. A dramatic 250-m-wide, very steep-walled crater with a jagged rim caps the volcano. The substantially higher SE rim forms the 1496 m high point of the island. Fresh-looking lava flows, prior to activity in 2009, had descended in all directions, often forming capes along the coast. Much of the lower-angle outer flanks of the volcano are overlain by pyroclastic-flow deposits. Eruptions have been recorded since the 1760s and include both quiet lava effusion and violent explosions. Large eruptions in 1946 and 2009 produced pyroclastic flows that reached the sea.

Sources: Sakhalin Volcanic Eruption Response Team (SVERT), Kamchatkan Volcanic Eruption Response Team (KVERT)