Geologic Background:
The island of Seguam is located about 1,750 km
SW of Anchorage in the central Aleutian Islands. The
elliptical, 11.5 x 24 km island contains two calderas,
each with a Holocene central volcano. A third Holocene
cone lies at the eastern end of the island. The 3-km-wide
westernmost caldera has a central cone, Pyre Peak, which
rises 1 km above the caldera floor and is the source of
most of the historical eruptions of Seguam volcano. A
very young basalt field surrounds Pyre Peak and lava
flows from the caldera have reached the southern coast.
The larger eastern caldera has a small, 300-m-high
central cone. The two Holocene cones east of Pyre Peak
are surrounded by fresh-looking andesitic and dacitic
lava flows.
Historic Activity:
- Eruptions in 1786, 1827, 1891, 1892, 1902, 1927, and
1977.
- In 1977 a 2.5-km-long fissure eruption occurred 2.5
km southeast of the peak.
- A thermally active region is located just south of
Pyre Peak.
Recent Activity:
- Small ash eruptions from a satellite cone 1.5 km
south of the west caldera's central cone (Pyre Peak) were
observed on Dec. 27 and 30, 1992 by the U.S. Coast
Guard.
- Additional small eruptive plumes were observed by the
Coast Guard on May 28 and June 2, 1993. Heavy ash
eruptions rising 900-1,200 m were reported by the U.S.
Coast Guard on the morning of July 31, 1993. A lava flow
was also noted. On August 19, 1993, U.S. Coast Guard
observers reported that Pyre Peak on Seguam Island was
continuing to erupt from a vent about 180 m below the
1,037-m summit. A dark ash plume over the volcano that
day reached an altitude of 2,500 m and drifted
ESE.
Data Sources:
- Smithsonian's Global Volcanism Network (V. 17, No. 12
to V. 18, No. 8).
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