Report on Shishaldin (United States) — 20 November-26 November 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 November-26 November 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, 20 November-26 November 2019. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
AVO reported that increased seismicity and higher surface temperatures at Shishaldin during 19-20 November indicated elevated eruptive activity. Seismicity abruptly dropped at 0340 on 20 November and remained low, heralding another pause in activity. Tremor and surface temperatures remained low through 23 November. Seismicity again increased during 24-25 November and small explosions were detected in local and regional infrasound stations. Strongly elevated surface temperatures were observed in multiple satellite images. A partial collapse of the summit cone sometime around 1430 on 24 November produced a pyroclastic flow that traveled as far as 3 km down the NW flank. A new lava flow on the NW flank was several hundred meters long. Seismicity decreased but remained elevated during 25-26 November. Strongly elevated surface temperatures were identified in multiple satellite images, and incandescence from the summit was occasionally visible in web camera images overnight. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
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.