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Report on Shishaldin (United States) — 5 May-11 May 2004


Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
5 May-11 May 2004
Managing Editor: Gari Mayberry

Please cite this report as:

Global Volcanism Program, 2004. Report on Shishaldin (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 5 May-11 May 2004. Smithsonian Institution and US Geological Survey.

Weekly Report (5 May-11 May 2004)


United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)

Seismic unrest continued at Shishaldin during 30 April to 7 May. It was characterized by sequences of volcanic earthquakes and seismic tremor. The number of airwaves recorded by the seismic network diminished in comparison to the previous week, but weaker signals were recorded. Thermal anomalies at the summit were observed on satellite imagery under optimal viewing conditions. Retrospective analysis confirmed that these data, as well as similar signals observed in January 2004, were the first thermal anomalies observed at Shishaldin since August 2000. AVO saw no signs that an eruption was imminent. Shishaldin remained at Concern Color Code Yellow.

Geological Summary. The symmetrical glacier-covered Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. It is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." Constructed atop an older glacially dissected edifice, 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. A steam plume often rises from the summit crater.

Source: US Geological Survey Alaska Volcano Observatory (AVO)