Report on Ukinrek Maars (United States) — May 1977
Natural Science Event Bulletin, vol. 2, no. 5 (May 1977)
Managing Editor: David Squires.
Ukinrek Maars (United States) Periodic earthquake swarms near the new vents
Please cite this report as:
Global Volcanism Program, 1977. Report on Ukinrek Maars (United States). In: Squires, D. (ed.), Natural Science Event Bulletin, 2:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197705-312131.
57.832°N, 156.51°W; summit elev. 91 m
All times are local (unless otherwise noted)
When visited in late May, the E vent was filling with water. A glow could be seen through fractures in the E vent dome, which had ceased growing and was degassing less vigorously than in mid-April. The vents are located on the Bruin Bay Fault. Its projected trend cuts an area of about 12 new hot springs that have formed about 3 km to the N in Becharof Lake. Periodic earthquake swarms continued to occur in the vicinity of the new vents. A third seismograph station was added in late May to the two installed in April.
Further References. Kienle, J., Kyle, P.R., Self, S., Motyka, R.J., and Lorenz, V., 1980, Ukinrek Maars, Alaska, I. April 1977 eruption sequence, petrology and tectonic setting: JVGR, v. 7, p. 11-38.
Kienle, J., and Swanson, S.E., 1983, Volcanism in the eastern Aleutian Arc: late Quaternary and Holocene centers, tectonic setting, and petrology: JVGR, v. 17, p. 393-432. (This reference also contains data on Augustine and Iliamna.)
Self, S., Kienle, J., and Huot, J.P., 1980, Ukinrek Maars, Alaska, II. Deposits and formation of the 1977 craters: JVGR, v. 17, p. 39-66.
Geologic Background. Ukinrek Maars are two explosion craters that were created in an area without previous volcanic activity during a 10-day-long phreatomagmatic eruption March-April 1977. The basaltic maars were erupted through glacial deposits in the Bering Sea lowlands 1.5 km south of Becharof Lake and 12 km west 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 north of Ukinrek maars and were the site of a phreatic eruption about 2300 years ago.
Information Contacts: J. Kienle, Univ. of Alaska.