Erosional features

Rocks frozen into the base of a glacier act like sandpaper to scratch and groove the bedrock in some places where glaciers have been.  Below are some examples of glacial erosion features going from small (smaller than your finger) to large (valley sized).

STRIATION, GROOVING, POLISH (Small scale features that include surface smoothing, scratching, and/or molding of bedrock.)

Linear features such as striations and grooving are parallel to the ice flow direction (like scratches would be). Water at the glacier bed is under pressure and can aid in the erosional process by smoothing surfaces and removing excess sediment.

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CHATTER MARKS (not concave, occur within grooves), CRESCENTIC GOUGES (concave upstream), LUNATE FRACTURES (concave downstream)

Chatter marks, crescentic gouges and lunate fractures are perpendicular to the ice flow direction and are made by the removal of a chip of bedrock likely due to a large rock embedded in the base of the glacier hitting the bedrock repeatedly (imagine a stone skipping on a water surface, but much slower, and more damaging).

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TRIMLINE (Vegetation is present above this line, and scraped away from the rock wall where the glacier was)

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ROCHE MOUTONNEE (also known as ‘sheepback’ because the mountain is gently sloping on one side (pointing against the ice-flow direction) and steep on the opposite side, giving it a profile that looks similar to a sheep eating grass.)

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CIRQUE (‘Bowl’-shaped head of a valley carved out by glacial erosion and quarrying.)

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U-SHAPED VALLEY (Glaciers carve U-shaped valleys whereas rivers carve V-shaped valleys.)

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FJORD (U-shaped valley that is now connected to the ocean.)

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One response to “Erosional features

  1. Pingback: Paws, chatter marks, and boots | Rock Paper Glacier!·

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