Report on Shishaldin (United States) — 25 March-31 March 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
25 March-31 March 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, 25 March-31 March 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 seismicity at Shishaldin continued to be elevated over background levels during 25-31 March, indicating that low-level eruptive activity confined to the summit crater likely continued. Nothing significant was observed in partly-to-mostly cloudy satellite and web camera images. Vigorous steaming at the summit was visible during 28 and 30-31 March; steam plumes, also reported by a pilot, rose several hundred feet above the crater on 30 March, and on 31 March observers on a Coast Guard ship reported that a steam-rich plume drifted 15-30 km S. 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.