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There are four types of coastal erosion:
Hydraulic action is the force of the waves against the cliffs. The water traps air in cracks and caves. The air is compressed, forcing the rock to weaken and eventually break.
Corrosion is caused by the acid in the seawater spray dissolving the rock.
Attrition is caused by pebbles hitting each other in the waves. This makes the pebbles smaller and rounder and eventually they become sand.
Abrasion is the effect of waves throwing pebbles at the cliffs. This erodes the cliffs at their base.
The features of erosion are:
Headlands and bays.
Caves, arches, stacks and stumps.
Headlands and Bays
Headlands and Bays
These are features of erosion and deposition.
1. Waves attack a discordant coastline of alternating hard and soft rock. The soft rock erodes at a faster rate than the hard rock.
2. Headlands are created from the hard rock and bays are eroded from the soft rock between them. Deposition also occurs in sheltered bays.
Caves, Arches, Stacks and Stumps
Caves, Arches, Stacks and Stumps
These are features of erosion.
1. Waves attack a fault in the rock by hydraulic action and abrasion.
2. The fault is enlarged to form a cave. A blowhole may appear on the headland due to upward erosion by waves on the roof of the cave.
3. Hydraulic action and abrasion widen and deepen the cave and eventually cut through the headland to form an arch.
4. Undercutting, weathering and gravity lead to collapse, leaving a stack.
5. Weathering and erosion turn the stack into a stump.
As the cliff retreats through erosion by waves, a platform of rock extending into the sea may be left. This is called a wave cut platform.
Wave Cut Platform
Wave Cut Platform
One of the most common features of a coastline is a cliff. Cliffs are shaped through a combination of erosion and weathering - the breakdown of rocks caused by weather conditions.
Soft rock, eg sand and clay, erodes easily to create gently sloping cliffs. Hard rock, eg chalk, is more resistant and erodes slowly to create steep cliffs.
The process of cliff erosion:Â
Weathering weakens the top of the cliff.
The sea attacks the base of the cliff forming a wave-cut notch.
The notch increases in size causing the cliff to collapse.
The backwash carries the rubble towards the sea forming a wave-cut platform.
The process repeats and the cliff continues to retreat.
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