As a geomorphic weathering process, plucking is a type of mass wasting which occurs as a glacier flows over a rocky outcrop it covers. "Plucking" refers to the removal of chunks of rock from the outcrop's lee side by brute mechanical force. Unlike freeze/thaw erosion, the flowing ice simply tears blocks of rock from the rock face, carrying them away to be deposited as glacial boulders somewhere else.
The diagram below shows a glacier plucking chunks from a buried outcrop, which may one day be exposed as a roche moutonnée (aka sheepback):
-> -> flow direction -> ->
--------- __________ -----------
---------- ____.----' | /'-.
________ ___.---' |__ / /
__.--' | | / / _________
-------- _.-' | |_ '-./
_.-' | |
_.-' |_
_.-' | | -------------
_.-' | |
_.-' | |
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