AVO reported that increased seismicity and higher surface temperatures at Shishaldin during 19-20 November indicated elevated eruptive activity. Seismicity abruptly dropped at 0340 on 20 November and remained low, heralding another pause in activity. Tremor and surface temperatures remained low through 23 November. Seismicity again increased during 24-25 November and small explosions were detected in local and regional infrasound stations. Strongly elevated surface temperatures were observed in multiple satellite images. A partial collapse of the summit cone sometime around 1430 on 24 November produced a pyroclastic flow that traveled as far as 3 km down the NW flank. A new lava flow on the NW flank was several hundred meters long. Seismicity decreased but remained elevated during 25-26 November. Strongly elevated surface temperatures were identified in multiple satellite images, and incandescence from the summit was occasionally visible in web camera images overnight. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological Summary. The symmetrical glacier-covered Shishaldin in the Aleutian Islands 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 edifice 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 covered 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.

Source: US Geological Survey Alaska Volcano Observatory (AVO)