Emission of large steam plumes, sometimes containing ash, were observed from aircraft and boats through August 1986. [The following reports describing activity at Shishaldin during 30 June-21 August 1986, were collected by John Reeder. Observers were Capt. Lee Goch (LG), Reeve Aleutian Airways; Capt. Jerry Chisum (JC), MarkAir; Jason Currier (JCu), on MarkAir flight; Theresa Dubber (TD) and Robert Senimore (RS), FAA, Cold Bay; and Tom Kizzia (TK), Anchorage Daily News aboard Alaska state ferry Tustumena.]

30 June (1900): White steam plume, drifting at least 5 km S. (LG)

19 July (1430): White steam plume with minor ash to 550 m above the summit, drifting more than 40 km E. (LG)

Mid-July: Steam with some ash drifted substantial distances. (JC)

20 August (1345): Voluminous steam with traces of ash. (JCu)

21 August (0900): 450-m white plume drifting SSE. (TD and RS)

21 August (afternoon): White plume to at least 450 m above the summit, drifting S at least 16 km. (TK)

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.