AVO reported that seismicity at Shishaldin continued to be elevated over background levels 15-21 April indicating that low-level eruptive activity confined to the summit crater likely continued. Cloud cover frequently prevented satellite and webcam observations. On 16 April the webcam periodically recorded a white steam plume rising about 500 m above the summit. Several pilot reports indicated ash emissions, prompting a SIGMET, however no ash was visible in satellite or webcam images, and seismicity remained unchanged. 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)