Glacial striation

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Glacial striations at Mount Rainier National Park
Glacial grooves stemming from the Wisconsin glaciation at Kelleys Island, Ohio

Glacial striations are scratches or gouges cut into bedrock by glacial abrasion.These scratches and gouges were first recognized as the result of a moving glacier in the late 1700s when Swiss alpinists first associated them with moving glaciers. They also noted that if they were visible today that the glaciers must also be receding.[1]

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. Finer sediments also in the base of the moving glacier further scour and polish the bedrock surface, forming a glacial pavement. Ice itself is not a hard enough material to change the shape of rock but because the ice has rock embedded in the basal surface it can effectively abrade the bedrock.

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.

Factors which affect the rate of glacial abrasion[edit]

The following affect the rate of abrasion:[1]

Gallery[edit]

Selwyn Rock 4
Overview of Selwyn Rock, South Australia - exhumed Permian glacial pavement 
Selwyn Rock - grooves and striations on exhumed glacial pavement 
Selwyn Rock - grooves and striations on exhumed glacial pavement 

References[edit]

  1. ^ a b Easterbrook, Don (1999). Surface Processes and Landforms. Upper Saddle River, New Jesey: Prentice Hall. pp. 315–317. ISBN 0-13-860958-6. 

External links[edit]

Media related to Glacial striation at Wikimedia Commons