Report on Ukinrek Maars (United States) — 12 May-18 May 2021
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 12 May-18 May 2021
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2021. Report on Ukinrek Maars (United States) (Sennert, S, ed.). Weekly Volcanic Activity Report, 12 May-18 May 2021. Smithsonian Institution and US Geological Survey.
57.832°N, 156.51°W; summit elev. 91 m
All times are local (unless otherwise noted)
On 12 May AVO changed the Aviation Color Code and Volcano Alert Level for Ukinrek-Maars to Green and Normal, respectively, reflecting that communication with seismic stations had been re-established, allowing for the location of earthquakes and detection of unrest.
Geological 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 wide 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.