Seguam

Geography & Climate

Seguam is located in United States, within the Aleutian Ridge Volcanic Arc of the broader North America Volcanic Regions. Situated at 52.31° N, 172.51° W in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,054 meters above sea level, Seguam is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Seguam sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in United States near Seguam, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Seguam has 13 recorded eruptions in the geological database, spanning from 7300 BCE to 1993 CE. The most powerful recorded event was a paroxysmal eruption with devastating regional consequences in 7300 BCE, reaching VEI 5 on the Volcanic Explosivity Index. Notable eruptions include 1902 CE (VEI 3), 1892 CE (VEI 3), 7300 BCE (VEI 5). This level of eruptive frequency indicates a persistently active volcanic system that warrants ongoing monitoring. The most recent eruption in 1993 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 5, Seguam has demonstrated the capacity for paroxysmal eruptions comparable to the 1980 eruption of Mount St. Helens. Eruptions of this scale can devastate areas within 20-30 kilometers and produce ash fall that disrupts aviation and agriculture across hundreds of kilometers. With 13 recorded eruptions, Seguam has a substantial eruptive history that provides valuable data for understanding volcanic behavior and assessing future hazards in the North America Volcanic Regions region. Given its recent activity, Seguam is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The 11.5 x 24 km island of Seguam, 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 9,000 years ago, leaving a caldera open to the west, inside which a rhyolitic cone was constructed. The 3 x 4 km westernmost caldera has a central scoria cone, Pyre Peak, which rises above the caldera rim and is the source of most of the reported eruptions. 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.

— Smithsonian Institution, Global Volcanism Program