Main features and landforms of glacial erosion.

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Kreeshan Annauth                Geography

Main features and landforms of glacial erosion.


Striations: When a glacier moves across the underlying rock, the process of abrasion wears it away. It is the fragments of rock held in the ice that do the abrading, scraping across the rock surface like nails across a wooden desk top. Larger rock fragments leave deep scratch marks behind them. These scratch marks are straight parallel lines that reveal the direction of ice movement.

Freshly exposed striations have a preferred orientation of rock grains. By lightly running a finger along the striation it is possible to discover that when moving one way along it, the rock feels smooth, but when moving the other way it feels coarser. The moving ice leaves the rock grains aligned with the direction of movement, so when the striation feels smooth, your finger is moving in the direction of ice flow. When the striation feels rough, you are moving against the ice flow. This test doesn't always work, and won’t work on striations that have been exposed for a long period of time.

Crag and tail: A crag and tail is a larger rock mass than a Roche moutonnee. Like a Roche moutonnee, it is formed from a section of rock that was more resistant than its surroundings. On the lee side of the resistant rock, the bed rock was protected from the erosional power of the glacier.

The volcanic rocks on which Edinburgh Castle (Scotland) is built provided protection against the erosion from an advancing glacier and Royal Mile, the main street in Edinburgh, extends along the gently downward sloping lee slope, or tail.

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Chatter Marks - Marks caused when rocks stuck in the base of the ice have removed thin flakes or chips from the bedrock surface.

P-Forms: These features, which extend several to tens of metres in length, are of uncertain origin. P-forms (P for ) are smooth-walled, linear depressions which may be straight, curved, or sometimes hairpin-shaped and measure tens of centimetres to metres in width and depth. Their cross sections are often semicircular to parabolic, and their walls are commonly striated.


Whalebacks:  Rock drumlins and streamlined spurs; these are smoothed areas of bedrock, attributed to unconfined glacier ...

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