Glacial striation
Glacial striations are scratches or gouges cut into bedrock by glacial abrasion. Glacial striations are usually multiple, straight, and parallel, representing the movement of the glacier using rock fragments and sand grains, embedded in the base of the glacier, as cutting tools. Large amounts of coarse gravel and boulders carried along underneath the glacier provide the abrasive power to cut trough-like glacial grooves, and finer sediments also in the base of the moving glacier further scour and polish the bedrock surface, forming a glacial pavement.
Most glacial striations were exposed by the retreat of glaciers since the Last Glacial Maximum or the more recent Little Ice Age. As well as indicating the direction of flow of the glacial ice, the depth and extent of weathering of the striations may be used to estimate the duration of post-glacier exposure of the rock.
An outstanding example of glacial grooves can be found at the Glacial Grooves at Kelleys Island, Ohio (a National Natural Landmark), the most impressive of which is 400 feet (120 m) long, 35 feet (11 m) wide, and up to 10 feet (3.0 m) deep. These grooves cut into the Columbus Limestone. Striations cover the sides and bottoms of the grooves.
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