We are currently having technical problems with the volcano profiles, Weekly Reports, and Current Eruptions pages, but expect to have them restored on 24 May. Sorry for the inconvenience.
Logo link to homepage

Report on Semisopochnoi (United States) — 2 June-8 June 2021


Semisopochnoi

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 2 June-8 June 2021
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2021. Report on Semisopochnoi (United States) (Sennert, S, ed.). Weekly Volcanic Activity Report, 2 June-8 June 2021. Smithsonian Institution and US Geological Survey.

Weekly Report (2 June-8 June 2021)

Semisopochnoi

United States

51.93°N, 179.58°E; summit elev. 1221 m

All times are local (unless otherwise noted)


AVO reported that low-level unrest at Semisopochnoi continued during 2-8 June with seismicity occasionally above background levels. Steaming from Mount Cerberus was sometimes observed by field crews. Slightly elevated surface temperatures were identified in a few satellite infrared images during 4-7 June. 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)