Report on Shishaldin (United States) — 25 September-1 October 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 September-1 October 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, 25 September-1 October 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 26 September AVO reported that seismicity at Shishaldin had decreased during the previous few weeks to levels slightly above background. Satellite images indicated decreased surface temperatures at the summit over the same period and showed collapse and slumping of the floor of the summit crater, suggesting a withdrawal of magma. Tiltmeter data suggested that the collapse may have occurred on 19 September. The Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory.
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.