Report on Shishaldin (United States) — 6 December-12 December 2017
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 December-12 December 2017
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2017. Report on Shishaldin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 December-12 December 2017. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
AVO increased the Aviation Color Code for Shishaldin to Yellow and the Volcano Alert Level to Advisory on 6 December following several weeks of increasing seismicity and pressure waves recorded by infrasound sensors. Continuous infrasound waves were detected for more than 10 hours on instruments located in Sand Point, ~230 km E. Steam emissions visible in satellite and webcam images during 5 and 8-12 December were rising hundreds of feet above the summit crater. The steam emissions were occasionally accompanied by infrasound signals indicating episodes of short-duration energetic gas emissions and/or small explosions.
Geologic Background. The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, 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 steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 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.