Volcano Type: Stratovolcanoes
Volcano Status: Historical
Last Known Eruption: 1993
Summit Elevation: 1054 m 3,458 feet
Latitude: 52.315°N 52°18’55″N
Longitude: 172.510°W 172°30’35″W
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.
Seguam Island consists of the remnants of two late Quaternary calderas. Holocene volcanic cones occur in both of the calderas and a third Holocene cone lies at the east end of the island. Pyre Peak, commonly referred to as Sequam volcano, highest of the young cones, dominates the western half of the island and occupies the center of the western caldera that is defined by remnants of a semi-circular ridge about 3 km in original diameter and about 700 m high. A Holocene basalt field surrounds Pyre Peak extending down to shoreline. This general area has been the site of most if not all historical volcanic activity. Late Quaternary lavas and pyroclastic rocks ranging in age form 1.1 Ma to 0.03 Ma underlie the basalt. The two Holocene cones to the east are surrounded by andesite and dacite lava flows with well preserved constructional features.
Originally posted 2010-08-21 05:01:15.
