Yunaska

Geography & Climate

Yunaska is located in United States, within the Aleutian Ridge Volcanic Arc of the broader North America Volcanic Regions. Situated at 52.64° N, 170.63° W in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 550 meters above sea level, Yunaska is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a shield, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Yunaska 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 Yunaska, 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

Yunaska has 6 recorded eruptions in the geological database, spanning from 1817 CE to 1937 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1937 CE, reaching VEI 3 on the Volcanic Explosivity Index. Notable eruptions include 1937 CE (VEI 3), 1824 CE (VEI 3). This eruption frequency indicates a moderately active volcanic system with periodic reawakenings. The most recent eruption in 1937 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Yunaska has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel. With 6 recorded eruptions on file, Yunaska has enough documented activity to help scientists identify patterns in its eruptive behavior.

GVP Reference Summary

The elongated 9 x 23 km Yunaska in the Islands of the Four Mountains group of the Aleutian Islands is comprised of two distinct volcanic centers. The older western center consists of the eroded remnants of four overlapping stratovolcanoes that form a linear, NNE-trending ridge. Cinder cones and fissure-fed lava flows extend from the western end of the complex. The younger eastern complex consists of a shield volcano capped by two nested calderas. The 3.5-km-wide Coats caldera is located within an older 10 x 13 km caldera and contains cinder cones and a lava field. Two areas of youthful lava flows extend down the flank through a gap in the SW caldera rim and cover the upper N flank of the caldera. Vents are found on the flanks of the caldera within a kilometer of its rim. A post-caldera cone is capped by a small summit crater. The eastern center is presumably the source of eruptions recorded since the early 1800s.

— Smithsonian Institution, Global Volcanism Program