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The U.S. Coast Guard at 11:04 Saturday reported an eruption at Seguam Volcano in the central Aleutian Islands about 1100 miles southwest of Anchorage. Heavy ash eruptions to 3,000 - 4,000 feet were reported along with a lava flow descending the flank of the volcano. Seguam was most recently active in late December, 1992 when small ash eruptions were reported from a flank cone a mile southwest of Pyre Peak, an active vent near the west-central part of the 15-mile-long island. This general area was also the site of a large outflow of lava in 1977. Seguam island is uninhabited.
Possible eruptive activity was reported late Friday afternoon July 30 at Mount Veniaminof Volcano on the Alaska Peninsula about 500 miles southwest of Anchorage. Observers in nearby Perryville, a small coastal village 21 miles southeast of the summit of the volcano about 14:30 ADT. A white steam cloud was present between spurts of black smoke. This type of activity continued into the evening. Perryville observers this morning (Saturday, July 31) reported seeing a gray cloud rising from the volcano and extending to the south. No pilot reports of ash clouds have been received and an ash cloud has no been reported on National Weather Service satellite imagery.
Veniaminof Volcano is a broad conical mountain truncated by a spectacular ice-filled summit caldera about 10 km in
diameter; the highest part of the caldera rim is about 8400 feet. An active intracaldera cone rises to an altitude of 7075 feEt (about 1000 feet above the surrounding ice-field) in the western part of the caldera. This cone was the site of the most recent eruption in 1983-84 and probably the site of the other 8 historic eruptions in 1838, 1852, 1892, 1930, 1939, 1944, and 1956.
The 1983-84 eruption began on June 2, 1983 and lasted to mid-April 1984 with a break in activity from mid-August to early October. The eruption was Strombolian in character with eruption clouds seldom reaching 20,000 feet above sea level. Lava flows from the summit crater of the intracaldera cone and adjacent subglacial thermal activity melted about 200 million cubic yards of ice forming a water-filled ice pit 3300 feet by 3300 feet and about 400 feet deep. The ice pit subsequently was partly filled by an estimated 52 million cubic yards of lava.
At the present time, the nature of the volcanic activity at Veniaminof is unknown. Assuming an eruption is occurring, it is likely to be similar to previous historic eruptions, i.e, the 1983-84 event. If this type of activity were to continue, occasional ash falls are possible at Perryville and pilots should be aware of ash clouds st elevations generally not exceeding 20,000 feet.
AVO has no seismic monitoring equipment on either Seguam or Veniaminof volcanoes and for this reason is not using the level of concern color code. AVO will continue to monitor the situation at the volcanoes through observations made by villagers, fishermen, pilots satellite imagery, and overflights if necessary.