File:Glacial striations from Pleistocene glaciation on Mud Lake sequence sedimentary rocks (Neoarchean; Bourgin Road roadcut, Virginia, Minnesota, USA) 1 (23416641471).jpg

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Pleistocene-aged glacial grooves on Precambrian sedimentary rocks in Minnesota, USA.

Glaciers are rivers of ice. Ice is a mineral (H2O). Glacial ice is a rock (technically, a metamorphic rock). Despite being solid, ice does flow under certain conditions at the Earth’s surface. Occasionally, Earth experiences Ice Ages, during which extensive ice sheets cover and move over significant portions of the Earth’s surface. As ice moves over landmasses, it erodes underlying rocks and picks up small to large pieces of debris. This debris accumulates at the base of the ice sheet and scrapes bedrock as the glacier moves, resulting in glacial scratches (glacial striations) (= thin scratch lines on rock) and glacial grooves (= large channels incised in rock).

The above photo shows a slightly metamorphosed shale-siltstone-graywacke outcrop that was eroded and glacially striated during the Pleistocene Ice Age.

Geologic unit & age: Mud Lake sequence, Neoarchean

Locality: roadcut along the eastern side of Bourgin Road roadcut, just southeast of the Rt. 53-Rt. 135 intersection, southeast of the town of Virginia, central St. Louis County, northeastern Minnesota, USA (47° 29’ 53.91” North, 92° 31’ 01.38” West)
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Source Glacial striations from Pleistocene glaciation on Mud Lake sequence sedimentary rocks (Neoarchean; Bourgin Road roadcut, Virginia, Minnesota, USA) 1
Author James St. John

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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/23416641471 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

5 December 2019

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current05:52, 5 December 2019Thumbnail for version as of 05:52, 5 December 20193,997 × 2,696 (4.28 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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