Report on Shishaldin (United States) — 22 May-28 May 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 22 May-28 May 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Shishaldin (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 22 May-28 May 2002. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
During 17-24 March, the number of locatable low-frequency seismic events at Shishaldin greatly decreased in comparison to the previous week, returning to background levels. Shishaldin remained at Concern Color Code Green ("volcano is in quiet, "dormant" state").
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.