Avak
Key facts
- Country
- United States
- Diameter
- 12 km
- Age
- less than about 95 million years
- Location
- 71.25° N, 156.50° W
Nothing: the structure is buried beneath the tundra near Utqiaġvik (formerly Barrow), on the Arctic coast of Alaska.
Avak is a buried impact structure about 12 km across on the North Slope of Alaska, close to the town of Utqiaġvik, the northernmost town in the United States. It is a reminder that impact craters can affect where people find energy resources.
Discovery. Avak was found during exploration for oil and gas in the 1940s and 1950s, when a test well drilled into the structure met heavily broken rock far below where it was expected, and seismic and gravity surveys showed a round disturbance. In the 1980s and 1990s, study of the cores showed shocked quartz with microscopic planar deformation features, as well as shatter cones, establishing that it was made by an impact.
What it hit. The impactor struck a thick sequence of sedimentary rocks, sandstones, mudstones and limestones of Palaeozoic to Cretaceous age. The rebound of the crater floor raised older rocks hundreds of metres in the centre. Younger sediments have since buried the whole structure. The youngest rocks affected are Cretaceous, so the impact took place less than about 95 million years ago, but its exact age is unknown.
Gas fields. Several small gas fields near Utqiaġvik, which supply the town with fuel, lie around the edge of the structure. The impact appears to have created traps in which gas collected.
Why it matters. Avak is the northernmost known impact structure in the United States and one of very few known in the Arctic. The impactor is unknown.
Did you know?
Gas fields around the edge of Avak have supplied fuel to the town of Utqiaġvik.
Avak was first noticed during oil exploration in the mid-twentieth century.
It is the northernmost known impact structure in the United States.