Report on Shishaldin (United States) — 8 July-14 July 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 July-14 July 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Shishaldin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 8 July-14 July 2009. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
On 10 July, AVO reported that a distinct thermal anomaly in Shishaldin's summit crater observed intermittently since January 2009 became more intense during the previous month. AVO raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. AVO also noted that seismicity had not increased, deformation was unchanged, and satellite observations showed no significant sulfur dioxide gas emissions. Some reports of steaming from the summit crater were received.
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.