Description

From Wood and Kienle (1990) ^[1] : "The St. Michael volcanic field is one of a number of late Tertiary and Quaternary, alkaline to subalkaline basaltic volcanic fields in the Bering Sea region of western Alaska. The volcanic field covers all of St. Michael and Stuart Islands, extending inland as far as the Golsovia and Kogok rivers. It consists of >55 cones and craters and numerous flat-lying flows and tuffs covering >3,000 square km. The section of flows has a maximum thickness of 40 m exposed in sea cliffs along Norton Sound, but is probably much thicker in the interior of the field. Most of the volcanic field consists of flat-lying tholeiitic or alkali-olivine basalt flows which appear to be erupted from broad shield volcanoes, such as those comprising St. Michael Mountain and Stuart Mountain. These older dissected shield volcanoes are ~4 km across and 150 m high. Young steep-sided cinder cones consisting of alkali-olivine basalt, basanite, or hawaiite overlie the flat-lying flows. The cones and flows surrounding Crater Mountain, in the western part of the field, consist of highly alkalic basanite containing lherzolite nodules. Most of the cones in "The Sisters" region are basanite or alkali olivine basalt, although a small group of cones ~4 km northeast of "The Sisters" are olivine tholeiite. The alkalic cones in "The Sisters" region are aligned east-west, possibly following a fracture. These young, small cones are 200-700 m across and ~40-75 m high. A Holocene flow and two associated cones in the south-central part of the volcanic field are tholeiite. Seven maar volcanoes occur on St. Michael Island in the northwest part of the field. The western half of Stuart Island is made of young tholeiitic aa flows, probably erupted from a vent at West Hill." Dall (1870) ^[2] notes that "The natives have a tradition that St. Michael's has been thrice submerged" indicating possibly very young volcanism.