Coastal Landforms: Erosion and Deposition Processes
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Coastal Landforms: Erosion and Deposition
Headlands and Bays
These forms occur along coasts that have alternating resistant (harder) rock and less resistant (softer) rock. Where there is resistant rock, the coast erodes less quickly, leaving a headland which sticks out into the sea. Where there is softer rock, erosion will be more rapid, and a bay will form. As the headland becomes more exposed to the full force of the wind and waves, it becomes more vulnerable (weak) to erosion than the sheltered bay.
Cliffs and Wave-Cut Platforms
Erosion is greatest when large waves break against the foot of a cliff. The foot of the cliff is undercut to form a wave-cut notch. As the notch gets larger, the cliff above it becomes increasingly unsupported and, in time, will collapse. As this process is repeated, the cliff will slowly retreat and usually increase in height. The gently sloping land left at the foot of the retreating cliff is called a wave-cut platform.
Caves, Arches, and Stacks
Although cliffs, especially where they form headlands, consist of resistant rock, they are still likely to contain areas of weakness. Areas of weakness will be the first to be worn away by the sea. A typical sequence shows how a weakness is enlarged to form a cave and, later, an arch where the sea cuts right through the headland. The arch is widened by the sea undercutting at its base. As the rock above the arch becomes unsupported, it collapses to form a stack. Further undercutting causes the stack to collapse, leaving only a stump.
How Do Landforms Result From Deposition by the Sea?
Deposition occurs in sheltered areas where the build-up of sand and shingle is greater than its removal. The most widespread coastal deposition feature is the beach. Although rocky beaches are formed by erosion, sand and shingle beaches result from deposition. The differences in steepness between sand and shingle beaches, and how material of different sizes is distributed on those beaches, are important:
Shingle Beach
- Steeper slope: Large shingle and pebbles are found at the top.
- Smaller shingle is found at the bottom.
- Coarser, larger material is carried to the top of the beach as the swash is usually stronger than the backwash.
Sandy Beach
- Gentler slope: Shingle is found at the top, fine sand at the bottom.
- The backwash carries smaller, finer material back down the beach.