Violently shakes the crags (5)

I believe the answer is:

rocks

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'violently shakes' is the definition.
'rocks' can be an answer for 'shakes' ('rock' can be a synonym of 'shake'). I am unsure of the 'violently' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for rocks that I've seen before include "Lumps of hard mineral matter" , "Shakes violently - perhaps to mod music" , "Sways; stuns" , "is brilliant" , "Causes shock to; diamonds" .)

I've seen this clue in The Irish Independent.

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