Anomalously large steam plumes with traces of ash have been noted for the past several months at Shishaldin by airline pilots and passengers. Diffuse ash layers extended from the volcano on 19 and 28 March, and steam and ash emission was seen on 6-7 May. Activity was less intense the next day, and had declined to minor steaming by 10 and 13 May. [See also 11:05].

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.

Information Contacts: J. Reeder, ADGGS.