Imuruk Lake Volc Field description and information

From Wood and Kienle (1990) ^[1]: "The Imuruk basaltic volcanic field consists of ~75 vents (mostly small cones) surrounded by lava flows. Cones generally fed a single flow, and range in height from as little as 3 m to as much as 30 m. Some cones are little more than spatter ramparts at the highest parts of flows. The largest, and most recent, cone is the Holocene Lost Jim cone which is 30 m high and surmounted by a crater 30 m in diameter and 12 m deep. There are a few small shield-shaped volcanoes which were also probably monogenetic. Representative of these are the Twin Calderas, which are 120 m high with craters 500 to 750 m in diameter and 15 to 35 m deep. Flows are generally pahoehoe and have surface relief averaging only a few meters. There are a few aa and block lava flows. Lava flows are a few to a few tens of meters thick at their distal ends and up to a few tens of kilometers long. Only two flows are young enough that their geometry can be recognized clearly: the Late Pleistocene Camille flow extends 39 km west from its vent, and the Holocene Lost Jim flow extends 35 km west and 9 km north of its vent and covers ~230 square km.

"Four major stratigraphic units have been recognized based on degree of weathering and nature of overlying deposits. From youngest to oldest these are: the Holocene Lost Jim Flow, the Pleistocene Camille Flow, and the Pliocene and early Pleistocene Gosling and Imuruk volcanics. The Lost Jim Flow erupted 1,655 yr BP, and the Gosling volcanics have ages of 0.9 and 0.8 Ma. The Imuruk volcanics have been dated at 5.7 to 2.2 Ma. A fifth unit, the Kugruk volcanics, is Oligocene and probably unrelated to late Cenozoic volcanism. Ages of the Gosling and Imuruk volcanics are typical of other basalt fields in the Bering Sea region. The Imuruk volcanics have the greatest areal extent of the lava units and cover nearly 2,300 square km. The Imuruk basalt field lies in an area of broad structural warping accompanied by normal faulting. Fault scarps as high as 30 m, and as long as 5 km, trend northwest and north-northeast cutting units as young as the Gosling volcanics.

"Geochemical data are sparse but suggest that among Quaternary basalts the older, more voluminous Imuruk volcanics are dominantly subalkaline while the younger, less voluminous basalts are mainly alkalic. The latter contains ultramafic nodules."