Report on Shishaldin (United States) — 4 December-10 December 2019
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 4 December-10 December 2019
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2019. Report on Shishaldin (United States) (Sennert, S, ed.). Weekly Volcanic Activity Report, 4 December-10 December 2019. 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 elevated surface temperatures at Shishaldin were identified in satellite images during 3-4 December consistent with lava effusion, and a pilot confirmed active lava flows on the flank. Continuous tremor was recorded by the seismic network during 4-5 December. Seismicity, including Strombolian explosion signals, continued to increase until 2100 on 5 December and then afterwards was characterized by episodic tremor bursts and occasional Strombolian activity. Intermittent, very minor, and low-level ash or steam emissions near the summit and along the N flank were visible in clear webcam views on 5 December. A new lava flow had traveled 1.4 km down the NW flank. The eruption either slowed or paused during 6-7 December as evidenced by decreased seismicity and slightly elevated surface temperatures in satellite data. Temperatures again increased and were slightly elevated during 7-9 December, likely signifying renewed lava effusion. 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.