Eagle Butte
Key facts
- Country
- Canada
- Diameter
- 10 km
- Age
- less than about 65 million years
- Location
- 49.70° N, 110.50° W
Nothing obvious: the structure lies under the rolling prairie of south-eastern Alberta, south of the town of Medicine Hat.
Eagle Butte is a buried impact structure about 10 km across in the prairie of south-eastern Alberta, in Canada.
Discovery. The structure was found by the oil and gas industry. Seismic surveys, which send sound waves into the ground and record the echoes from rock layers, showed a round area where the normally flat layers were broken, with a raised centre. Wells drilled into the centre brought up rock containing shatter cones, cone-shaped fractures that form only under the shock of an impact, and the structure was described as an impact crater in the 1990s.
What it hit. The impactor struck a thick pile of sedimentary rocks, sandstones and shales of Cretaceous age lying on older Palaeozoic carbonates. In the centre, the rebound of the crater floor lifted older layers by several hundred metres. Erosion, including the scouring of ice sheets, has since removed the upper part of the structure, and glacial deposits now cover it.
Age. The youngest rocks disturbed by the impact are of latest Cretaceous age, so the impact happened less than about 65 million years ago. Its exact age is unknown.
Why it matters. Eagle Butte is one of a group of impact structures in western Canada that were found only because of the dense network of seismic surveys made in the search for oil and gas. The impactor is unknown.
Did you know?
Eagle Butte was found in seismic surveys made while searching for oil and gas.
Shatter cones were recovered from wells drilled into its centre.
The impact happened after the end of the age of the dinosaurs.