AVO reported that low-level eruptive activity at Semisopochnoi's North Cerberus cone continued during 18-25 January. Seismicity was elevated, characterized by periods of tremor and low-frequency earthquakes. Steam emissions were periodically visible in webcam images during 18-19 January and minor explosions were recorded by local seismic and infrasound sensors on 19 January. Steam and low-level ash emissions were visible in webcam and satellite images during 20-25 January. Daily explosions were recorded during 21-25 January, and elevated surface temperatures were identified in satellite data during 22-23 January. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological Summary. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked Mount Cerberus (renamed Mount Young in 2023) was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Source: US Geological Survey Alaska Volcano Observatory (AVO)