Report on Shishaldin (United States) — 24 July-30 July 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 24 July-30 July 2019
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2019. Report on Shishaldin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 24 July-30 July 2019. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
On 23 July field crews observed minor spattering and surface lava flows in Shishaldin’s summit crater during an overflight, prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. Elevated surface temperatures were observed in multiple satellite images during 24-30 July, though views were sometimes obscured by weather clouds. Nearly continuous weak seismic tremor was detected, and occasional infrasound signals consistent with small Strombolian explosions were recorded during 26-27 July.
Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.