Hydraulic Action
A mechanical erosion process where water pressure in cracks and crevices compresses trapped air, which then explosively expands when waves recede, fracturing rock. This process is most effective in fractured or jointed rock.
Real World
At Lulworth Cove in Dorset, hydraulic action has exploited a narrow band of weakly jointed Portland limestone, blasting open the original sea cave that eventually became the cove itself.
Exam Focus
Distinguish hydraulic action from abrasion clearly — examiners penalise conflation; emphasise compressed air and pressure release, not sediment contact.
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