Report on Shishaldin (United States) — 6 September-12 September 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 6 September-12 September 2023
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2023. Report on Shishaldin (United States) (Sennert, S, ed.). Weekly Volcanic Activity Report, 6 September-12 September 2023. 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 the eruption at Shishaldin continued during 6-12 September. Seismicity remains elevated and characterized by weak but steady tremor, small low-frequency earthquakes, and small explosions; explosions were not reported on 12 September. Elevated surface temperatures were identified daily in satellite images and were sometimes intense. A Significant Meteorological Information (SIGMET) notice issued on 6 September advised aircraft of a low-level ash plume drifting SSE at 1.5-1.8 km (5,000-6,000 ft) a.s.l. Small plumes visible in webcam images drifted ESE and SSE during 6-7 September. Additional small diffuse steam-and-gas plumes from the summit were observed in web camera images during 9-11 September. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).
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.