Report on Shishaldin (United States) — 1 January-7 January 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 1 January-7 January 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Shishaldin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 1 January-7 January 2020. 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 1-7 January. Seismicity was low during 1-2 January and elevated surface temperatures identified in several satellite images indicated continuing lava effusion. Seismicity began increasing at 0930 on 3 January and within several hours a brief period of sustained ash emissions produced plumes that rose as high as 8.2 km (27,000 ft) a.s.l. and drifted about 120 km SE. The ash plume produced minor amounts of volcanic lightning. Seismicity declined abruptly after the event. Satellite images acquired the next day showed no noteworthy activity; ash deposits from the day before mantled the upper flanks, lahars on the upper parts of the edifice and on the SW flank were visible, and lava flows on the upper NW and NE flanks were 1-2 km long. During 5-6 January seismicity was low but above background levels and elevated surface temperatures were visible in satellite images. A photo taken from Cold Bay (93 km NE) on 6 January showed glowing lava flows on the flank.
Seismicity increased at around 0500 on 7 January and was followed by observations of an ash plume drifting NE at an altitude of about 5.8 km (19,000 ft) a.s.l. Seismicity then decreased for a few hours. Another episode of elevated seismicity was accompanied by an increase in the altitude of the ash plume; it rose to 7.6 km (25,000 ft) a.s.l. and seemed to have a denser ash content. The Aviation Color Code was raised to Red and the Volcano Alert Level was raised to Warning. Volcanic lighting was detected in the cloud and volcanic infrasound signals were detected at regional stations. Seismcity significantly decreased around 1200 and remained low. Later that day the Aviation Color Code was lowered to Orange and the Volcano Alert Level was lowered to Watch.
Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 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 steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, 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.