Report on Shishaldin (United States) — 28 July-3 August 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 July-3 August 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, 28 July-3 August 2004. Smithsonian Institution and US Geological Survey.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
Low-level seismic tremor continued at Shishaldin during 22-30 July as it had for several months. On 24 July an AVO field crew observed vigorous steaming at the summit and what may have been ash deposits on the volcano's upper slopes. Shishaldin remained at Concern Color Code Yellow.
Geologic Background. The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, 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 steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 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.