Steam plumes that sometimes contained ash were observed by airplane pilots in early October 1986. [The following reports describing activity at Shishaldin during 2-10 October 1986 were collected by John Reeder. Observers were Capts. Jerry Chisum (JC) and Clint Schoenleber (CS), MarkAir; Stephanie Madsen (SM), Aleutian Air; Capts. Harold Black (HB), Lee Goch (LG), and James Fredenhagen (JF), Reeve Aleutian Airways; and John Reeder, ADDGS (JR).]

2 October (AM and PM): Above-average steam explosions with minor ash. (JC)

2 October (1145): Steam plume with minor ash extending at least 15 km SW. (SM)

3 October (1330-1336): Narrow steam plume to 400 m height; thin steam-and-ash plume drifted more than 40 km ESE; anomalous steam puffs with minor ash noted by JR at 1331-1332 and 1336. (HB, JR)

4 October (1520): Steam explosions sent plume to 800 m above the volcano; plume of vapor and minor ash extended about 50 km SSE; small amounts of black ash coated snow on N and NW flanks. (LG, JF, JR)

8 October: Normal 50-m steam plume. (CS)

10 October: Normal 50-m steam plume. (CS)

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.