On 15 February at 1600, Marsha Brown observed a large dark-gray plume rising at least 600 m above the summit, drifting ENE. The plume had not been evident 2 hours earlier and lasted until at least 1830. Larger-than-average steam plumes were later observed on 21 and 26 February and 3 March. [The following reports describing activity at Shishaldin during 15 February-3 March 1987 were collected by John Reeder. Observers were Marsha Brown (MB) and Theresa Dubber (TD), FAA, Cold Bay; and Andy Livingston (AL), Don Munson (DM), and Lee Goch (LG), Reeve Aleutian Airways.]

15 February (1600): 600-m-high plume to the ENE. (MB)

21 February (1314): 150-m-high plume to the NE. (JF, AL)

26 February (0925): 300-m-high plume to the SW. (TD)

2 March (1254): Minor steam to the SW. (JF, DM)

3 March (1240): 300-m-high plume extending 20 km ENE. (LG)

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.