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Report on Semisopochnoi (United States) — 1 April-7 April 2020

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 1 April-7 April 2020
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2020. Report on Semisopochnoi (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 1 April-7 April 2020. Smithsonian Institution and US Geological Survey.

Volcano Profile |  Weekly Report (1 April-7 April 2020)


Semisopochnoi

United States

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

All times are local (unless otherwise noted)


On 1 April AVO reported that seismic, infrasound, and satellite data collected during the previous two weeks indicated no signs of eruptive activity at Semisopochnoi; the Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory. A crater lake and robust steam plume were both identified in recent satellite images.

Geologic Background. 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 volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus 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 historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Source: US Geological Survey Alaska Volcano Observatory (AVO)