Ukinrek Maars

Geography & Climate

Ukinrek Maars is located in United States, within the Alaska Peninsula Volcanic Arc of the broader North America Volcanic Regions. Situated at 57.83° N, 156.52° W in the Northern Hemisphere, the volcano lies within a subarctic climate zone. At just 91 meters above sea level, Ukinrek Maars is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. The volcanic landform is characterized as a minor (basaltic), which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Ukinrek Maars 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 Ukinrek Maars, 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 basalt / picro-basalt, 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

Ukinrek Maars has 2 recorded eruptions in the geological database, spanning from 350 BCE to 1977 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1977 CE, reaching VEI 3 on the Volcanic Explosivity Index. These eruptions span roughly 2,327 years of volcanic history. The most recent eruption in 1977 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Ukinrek Maars 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. Given its recent activity, Ukinrek Maars is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

Ukinrek Maars are two explosion craters that were created in an area without previous volcanic activity during a 10-day phreatomagmatic eruption March-April 1977. The basaltic maars were erupted through glacial deposits in the Bering Sea lowlands 1.5 km S of Becharof Lake and 12 km W of Peulik volcano; their location is related to the regional Bruin Bay fault. The elliptical West Maar, which was the first to form, is 105 x 170 m and 35 m deep. The other maar, 600 m to the east, is 300 m wide and 70 m deep. Both maars are now filled by crater lakes; the eastern lake encircles a 49-m-high lava dome that was emplaced at the end of the eruption. Base surges were directed primarily to the NW. Juvenile material from the Ukinrek eruptions was of mantle-derived olivine basaltic composition. The dacitic Gas Rocks lava domes, of Quaternary age, are located on the shores of Becharof Lake, 3 km N of Ukinrek maars and were the site of a phreatic eruption about 2,300 years ago.

— Smithsonian Institution, Global Volcanism Program