Avak crater
Avak is an impact crater centered approximately southeast of Utqiagvik, Alaska, United States. Avak is a subcircular structure about in diameter and deep. In the structure, metamorphic basement rocks and regionally flat lying sedimentary rocks are uplifted and intensely deformed. The Avak structure has no surface expression in the swampy, lake-dotted tundra of the Arctic coastal plain. The structure is covered by a thin veneer of permanently frozen Pliocene and Pleistocene rock. This means that the age of the impact took place anywhere between 95 million and 3 million years ago. Palynological data on its ejecta suggest  Middle–Late Turonian age of the impact (about 90 million years ago). The Avak structure provides the structural trap for the natural gas in the adjacent South Barrow and East Barrow gas fields. These fields have accumulated about 37 bcf of natural gas in Jurassic sandstones. History. The Avak structure was first recognized from seismic surveys in the National Petroleum Reserve No. 4 (NPR4) by the U.S. Navy during the period from 1943 to 1953. The Navy drilled the Avak 1 well in 1951–1952, and encountered deformed rocks from near the surface to a total depth of . Shatter cones and  other evidence of impact origin was found. In 1995, geologists from the Geological Survey of Canada and U.S. Geological Survey found another group of mineralogic features that indicated that Avak is a meteorite impact structure: the planar deformation features.