On 30 March, explosions were reported at 1500 and 1720 from a vent 13 km [but see 2:4] NW of Peulik volcano. The latter explosion was viewed from close range from a Wien Air Alaska plane. Its crew reported that the dense, ash-laden eruption cloud rose higher than 6,000 m. Peulik, an 1,844-m stratovolcano with a dacite lava dome, last erupted in 1852. It is surrounded by several small olivine andesite scoria cones.

Information Contacts: T. Miller, USGS, Anchorage.

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 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.