Report on Seguam (United States) — August 1993
Bulletin of the Global Volcanism Network, vol. 18, no. 8 (August 1993)
Managing Editor: Edward Venzke.
Seguam (United States) Ash eruption to 2,500 m altitude
Please cite this report as:
Global Volcanism Program, 1993. Report on Seguam (United States). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 18:8. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199308-311180.
52.315°N, 172.51°W; summit elev. 1054 m
All times are local (unless otherwise noted)
On 19 August, U.S. Coast Guard observers reported that Pyre Peak . . . was continuing to erupt from a vent ~180 m below the summit. A dark ash plume over the volcano that day reached an altitude of 2,500 m and drifted ESE. No reports of ashfall in the sparsely populated region were received. U.S. Coast Guard observers reported that Pyre Peak was continuing to erupt in late August, but poor weather conditions prevented observers from confirming continued activity through 3 September. Frequent poor weather and limited air traffic combine to make tracking of activity at this remote island volcano difficult.
Geologic Background. The elliptical, 11.5 x 24 km island of Seguam, lying between Amlia and Amukta Islands in the central Aleutians, contains two calderas with Holocene post-caldera cones. Growth of the basaltic-to-rhyolitic Wilcox volcano on the east side of the island during the late Pleistocene was followed by edifice collapse and an associated ignimbrite eruption about 9000 years ago, leaving a horseshoe-shaped caldera open to the west, inside which a rhyolitic cone was constructed. The 3 x 4 km wide westernmost caldera has a central scoria cone, Pyre Peak, which rises above the caldera rim and is the source of most of the historical eruptions of Seguam volcano. A very young basaltic field surrounds Pyre Peak, and lava flows partially fill the caldera and reach the southern coast. Older Holocene lava flows were erupted from vents within the eastern caldera, and a monogenetic Holocene cone forms Moundhill volcano on the eastern tip of the island.
Information Contacts: AVO.