Report on Shishaldin (United States) — 19 August-25 August 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
19 August-25 August 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Shishaldin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 19 August-25 August 2015. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
AVO reported that on 18 August a field crew conducting gas measurements at Shishaldin observed a low-level plume from the summit drifting several kilometers downwind. Seismicity continued to be elevated over background levels during 19-25 August indicating that low-level eruptive activity confined to the summit crater continued. Cloud cover mostly prevented satellite and webcam observations; elevated surface temperatures were occasionally detected in satellite images. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
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.