Coastal Erosion Landforms

Coastal erosion creates some of the UK's most dramatic and recognisable landforms. This lesson examines how headlands and bays, wave-cut platforms, caves, arches, stacks, and stumps, and different types of cliffs are formed by the interaction of erosion, weathering, and mass movement.

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Differential Erosion: Headlands and Bays

When a coastline is made up of alternating bands of hard and soft rock running perpendicular to the sea (a discordant coastline), the softer rock is eroded more quickly than the harder rock. This creates a pattern of headlands (jutting out) and bays (set back).

Formation Process

1. Waves attack the coastline, which consists of alternating hard and soft rock.
2. The soft rock (e.g., clay, sand) is eroded more quickly by hydraulic action and abrasion, forming an indentation — a bay.
3. The hard rock (e.g., limestone, granite) resists erosion and is left jutting out into the sea — a headland.
4. Once formed, headlands receive concentrated wave energy because waves refract (bend) around them.
5. Meanwhile, bays are sheltered from wave energy, so deposition occurs, forming beaches.

graph TD
    A["Alternating hard<br/>and soft rock<br/>at the coast"] --> B["Waves erode<br/>soft rock faster"]
    B --> C["Bays form in<br/>soft rock — sheltered,<br/>deposition occurs"]
    B --> D["Headlands form in<br/>hard rock — exposed,<br/>erosion concentrated"]
    D --> E["Wave refraction<br/>focuses energy on<br/>headland sides"]
    E --> F["Headland gradually<br/>eroded — caves,<br/>arches, stacks form"]

UK Example: The Dorset Coast (Jurassic Coast)

The Dorset coast is a World Heritage Site that provides textbook examples of differential erosion:

Location	Rock Type	Landform
Lulworth Cove	Limestone (hard) backed by clay (soft) and chalk (medium)	Almost circular bay formed when the sea broke through the hard limestone barrier and rapidly eroded the softer clay behind
Durdle Door	Portland limestone (hard)	Natural arch in hard limestone headland
Studland Bay	Sand and clay (soft)	Wide, sheltered bay with sandy beaches
The Foreland (Old Harry Rocks)	Chalk (medium-hard)	Headland with stacks and stumps
Swanage Bay	Clay and sand (soft)	Bay with a sandy beach

Exam Tip: Lulworth Cove is a particularly good example to use in exams because it shows multiple rock types in a small area. The original limestone barrier has been breached by the sea, allowing rapid erosion of the softer clay behind, creating the distinctive cove shape. Knowing this level of detail impresses examiners.

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Wave-Cut Platforms and Notches

Wave-cut platforms (also called shore platforms) are flat areas of rock found at the base of retreating cliffs. They are one of the most common coastal erosion landforms in the UK.

Formation Process

1. Destructive waves attack the base of a cliff through hydraulic action and abrasion.
2. A wave-cut notch is eroded at the base of the cliff, typically between the high and low tide marks.
3. The rock above the notch becomes unsupported and increasingly unstable.
4. Eventually, the overhanging rock collapses through mass movement (rockfall or sliding).
5. The collapsed debris is broken down and removed by waves through erosion and transport.
6. The cliff face retreats (moves landward), and the process repeats.
7. Each cycle of notch cutting and cliff collapse extends the wave-cut platform — a gently sloping (typically 1-3°), flat rock surface extending seaward from the cliff base.

Wave-cut platforms are limited in width (usually no more than 500 m) because as the platform extends, waves must travel further across it, losing energy through friction. Eventually, waves reaching the cliff no longer have enough energy to erode a new notch effectively.

UK Examples

• Flamborough Head (East Yorkshire) — chalk cliffs with extensive wave-cut platforms visible at low tide.
• Robin Hood's Bay (North Yorkshire) — platforms exposed in sedimentary rocks.
• Southerndown (South Wales) — limestone platforms stretching up to 300 m from the cliff base.

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Caves, Arches, Stacks, and Stumps

This is one of the most commonly examined sequences of landform development in GCSE Geography. It shows how a headland is progressively eroded.

The Formation Sequence

Stage	Landform	How It Forms
1	Crack	Waves exploit a weakness in the headland (a joint, fault, or area of softer rock). Hydraulic action and abrasion widen the crack.
2	Cave	Continued erosion deepens the crack into a cave. Hydraulic action compresses air at the back of the cave, and abrasion widens it further. Chemical weathering (solution) may also contribute if the rock is limestone or chalk.
3	Arch	If the headland is narrow enough, caves on opposite sides may erode through to meet, creating an arch — a bridge of rock over the sea. Weathering attacks the roof of the arch from above.
4	Stack	The roof of the arch becomes too thin to support its own weight and collapses, leaving an isolated pillar of rock — a stack — standing in the sea, separated from the headland.
5	Stump	The stack is attacked at its base by wave erosion and weakened by weathering. It eventually collapses to form a low, flat stump, visible only at low tide. Over time, even the stump is eroded away.

Exam Tip: This sequence is so commonly examined that you should be able to draw and annotate a diagram showing all five stages from memory. Always include process labels (hydraulic action, abrasion, weathering) — not just landform names.

UK Case Study: Old Harry Rocks, Dorset

Old Harry Rocks at the eastern end of the Isle of Purbeck in Dorset is a classic example of this sequence: