6533b86efe1ef96bd12cb217

RESEARCH PRODUCT

Syn- and post-eruptive mechanism of the Alaskan Ukinrek Maars in 1977

subject

description

The two alkali olivine basaltic Ukinrek Maars (East Maar and West Maar) and one scoria cone within East Maar erupted within eleven days (March 30–April 9, 1977) on the Alaskan Peninsula, 13 km north of Mt. Peulik, an andesite volcano of the Aleutian Range. The East Maar, with a diameter of 300 m, is located within a small graben system striking N 1100 E, oblique to the Aleutian trench in a distance of 350 km. On these tensional faults two eruption centres occur: The East Maar and a scoria cone on the southeastern margin of its crater bottom. The scoria cone was active more or less during the whole eruption activity of East Maar. The West Maar, with a diameter of 140 m, is located just west of the East Maar. In the West Maar, after the first of three eruption cycles, feeder dike fragments were thrown out. They indicate that the explosion chamber migrated downwards during the maar formation. After the eruption activity, both craters filled up with ground-water and the coneshaped talus fans continued to grow on the crater floors, modified by gravity sliding and lahars.