glacial grooves
Kelley's Island's glacial grooves are a National Natural Landmark. They were developed around 18,000 years ago during the last Ice Age and are the world's largest known glacial striations. Glacial striations are typically generated when boulders and gravel are dragged across bedrock by the great weight of a glacier. These natural markings are used by geologists to establish the direction in which the now-melted ice previously flowed.
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