Tunnunik
Key facts
- Country
- Canada
- Diameter
- 25 km
- Age
- about 430 to 450 million years
- Location
- 72.47° N, 113.93° W
Steeply tilted rock layers and shatter cones in barren Arctic tundra on Victoria Island, Northwest Territories, in a region where the rocks are normally flat.
Tunnunik, formerly called the Prince Albert structure, is an eroded impact structure about 25 km across on the Prince Albert Peninsula of Victoria Island, in Canada's Northwest Territories. It is one of the most recently recognised impact structures in Canada.
Discovery. In 2010 geologists working in the area noticed that the normally flat-lying sedimentary rocks of the Arctic islands were, in one place, steeply tilted and even standing on end in a rough circle. On the ground they found shatter cones, cone-shaped fractures with branching grooves that form only under the shock of an impact. The discovery was announced in 2012.
What it hit. The target was a thick sequence of early Palaeozoic sedimentary rocks, mainly dolomites, limestones and sandstones, deposited in ancient seas. The impact lifted and folded these layers into a central uplift surrounded by a ring of faulted rock. Erosion has since removed the crater rim and the top of the structure, leaving the deeper levels exposed in the tundra.
Age. The youngest rocks affected are Ordovician, and measurements of the ancient magnetism locked into rocks altered by the impact point to an age of roughly 430 to 450 million years, in the late Ordovician or early Silurian. Some studies allow a younger age, so it is not precisely known.
Why it matters. Tunnunik shows how many impact structures may still lie unnoticed in remote parts of the world, waiting for geologists to pass by. The impactor is unknown.
Visiting. The site is extremely remote and can be reached only by aircraft. It lies within the traditional lands of the Inuvialuit.
Did you know?
Tunnunik was spotted in 2010 because flat Arctic rock layers were unexpectedly tilted on end.
It was originally named the Prince Albert structure.
Its age was estimated partly from ancient magnetism locked into the rocks.