Kara
Key facts
- Country
- Russia
- Diameter
- 65 km
- Age
- about 70 million years
- Location
- 69.10° N, 64.15° E
A low, eroded basin in Arctic tundra near the Kara Sea coast, with outcrops of impact breccia and melt rock along rivers.
The Kara structure lies on the Arctic coast of Russia, at the northern end of the Pai-Khoi hills near the Kara Sea, west of the Ural Mountains' northern tip. It is a large, eroded impact crater in a remote landscape of tundra, permafrost and slow, winding rivers.
The impact. Kara formed roughly 70 million years ago, in the Late Cretaceous, when dinosaurs still roamed the land. The crater is estimated at about 65 km across, although the original size is uncertain because erosion has removed much of the structure. Rocks inside the crater include thick deposits of impact breccia, rock made of broken fragments cemented together, and impactites, rocks transformed or melted by the impact. Like Popigai in Siberia, Kara's impactites contain tiny impact diamonds, formed when carbon in the target rocks was suddenly squeezed by the shock wave.
A close call with history. In the 1970s and 1980s, before the Chicxulub crater was identified, Kara was considered a possible cause of the mass extinction at the end of the Cretaceous. Early age measurements seemed to fit. More precise dating later showed that Kara is several million years older than the extinction, ruling it out. The discovery of Chicxulub in Mexico, with an age that matches the extinction precisely, settled the question.
One crater or two? A second structure called Ust-Kara, partly offshore under the Kara Sea, was once described as a separate crater formed at the same time, perhaps by a pair of impactors. Later studies concluded that Ust-Kara is not a separate crater, and it is now generally treated as part of the main Kara structure or as a misinterpretation of the geology.
Recognition. Soviet geologists identified Kara as an impact structure in the 1970s, based on shocked minerals and the distinctive impact rocks. Its remoteness has limited detailed study compared with more accessible craters, but it remains one of the larger confirmed impact structures in Europe and northern Asia.
Why it matters. Kara is a good example of how scientific ideas are tested and revised. A crater once suspected of causing a famous extinction was cleared by better dating. Its impact diamonds also add to our understanding of how shock waves transform carbon-bearing rocks, a process that has been studied at Popigai, Ries and elsewhere.
Seeing it today. Kara lies far from roads and towns in a harsh Arctic climate. Visits are rare and mostly made by scientific expeditions during the brief summer.
Did you know?
Kara was once a suspect for the extinction of the dinosaurs, until better dating ruled it out.
Its impact rocks contain tiny diamonds made by the shock of the collision.
The structure lies in Arctic tundra underlain by permafrost.