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Spec mapping (AQA 7037): Paper 1, §3.1.3 Coastal Systems and Landscapes — landforms of coastal erosion: cliffs and wave-cut/shore platforms; caves, arches, stacks and stumps; headlands and bays, together with the influence of geological structure (concordant and discordant coasts) on landform. These landforms are the outputs of the erosional transfers in Lesson 3, sculpted on the geological template developed in Lesson 8. The lesson links synoptically to §3.1.4 Glacial Systems (comparable structural control of erosional landforms in glaciated uplands) and reuses the wave-refraction physics from Lesson 2. The dominant Assessment Objectives are AO1 (knowledge of each landform and its formation sequence) and AO2 (explaining how process and structure combine, and how landforms evolve through time). The map-based exercise exercises AO3 (interpreting geological structure from a map to predict landform).
Why this lesson matters. AQA mark schemes for landform questions reward two things above all: a correct process sequence and place-specific detail. A generic "caves become arches become stacks" answer with no named example sits in the middle band; the same sequence anchored to Old Harry Rocks, with the chalk geology, the joint control and the collapse of Old Harry's Wife in 1896, reaches the top. This lesson supplies both the sequences and the located evidence.
Cliffs are the most widespread erosional landform on the coast. Their form depends on the interplay between marine erosion at the base and sub-aerial processes acting on the cliff face.
The process of cliff formation follows a well-established sequence, first described in detail by Sunamura (1992):
graph LR
subgraph "Cliff Retreat Sequence"
A["1. Wave attack at cliff base"] --> B["2. Wave-cut notch forms"]
B --> C["3. Overhang collapses"]
C --> D["4. Debris removed by waves"]
D --> E["5. Cliff retreats, platform extends"]
E --> A
end
As the cliff retreats, it leaves behind a gently sloping rock surface — the wave-cut platform. Key characteristics include:
Key Definition: A wave-cut platform (shore platform) is a gently sloping rock surface extending seaward from the base of a retreating cliff, formed by the progressive removal of rock through erosion.
The shape of a cliff profile depends on the balance between marine erosion at the base and sub-aerial weathering and mass movement on the face:
| Cliff Type | Profile | Dominant Processes | Example |
|---|---|---|---|
| Vertical/near-vertical | Steep, sheer face | Strong marine erosion; resistant rock | Beachy Head, East Sussex (chalk, 162 m high) |
| Sloping | Angled face, 40-70° | Sub-aerial processes dominate; softer rock | Barton-on-Sea, Hampshire (clay) |
| Terraced/benched | Stepped profile with horizontal ledges | Alternating resistant and weak rock layers | Lulworth, Dorset (Portland stone over Purbeck beds) |
| Composite | Complex profile with multiple angles | Variable geology; multiple processes | Robin Hood's Bay, Yorkshire |
The profile of a cliff is determined by several interacting factors:
Rock resistance: Hard rocks (granite, basalt, limestone) maintain steep profiles because marine erosion at the base outpaces sub-aerial weathering on the face. Soft rocks (clay, sand, glacial till) develop more gentle slopes because weathering and mass movement are rapid relative to marine erosion.
Geological structure: The orientation of bedding planes, joints and faults has a profound effect:
| Bed Orientation | Effect | Resulting Profile |
|---|---|---|
| Horizontal beds | Uniform resistance across cliff face | Vertical cliff with horizontal ledges |
| Beds dipping inland | Stable — rock layers lean into the cliff | Steep, stable cliff |
| Beds dipping seaward | Unstable — rock layers slide towards the sea | Prone to landslides; gentler profile |
| Beds dipping steeply (near vertical) | Erosion follows weaker beds | Irregular, often castellated profile |
Vegetation: Plant cover on the cliff face and top stabilises soil, intercepts rainfall and reduces surface runoff. Removal of vegetation (by erosion, human activity or grazing) accelerates mass movement.
It is useful to contrast two end-member cliff systems, because the dominant process — and therefore the resulting form — differs fundamentally:
| Attribute | Marine-dominated (high-energy) cliff | Sub-aerially-dominated (low-energy/soft) cliff |
|---|---|---|
| Rock | Resistant (chalk, limestone, granite) | Weak (clay, glacial till, sand) |
| Dominant process | Marine erosion at the base outpaces weathering of the face | Weathering and mass movement of the face outpace marine removal |
| Profile | Steep to vertical; bare rock face | Gentle, slumped, often vegetated; convex–concave |
| Example | Beachy Head (162 m vertical chalk) | Barton-on-Sea (slumped Barton Clay) |
| Retreat style | Episodic rockfall from a maintained steep face | Rotational slump and mudflow reshaping the whole face |
This contrast matters because the same landform name — "cliff" — describes two very different systems. On a marine-dominated cliff, the wave-cut platform is well developed and the cliff stays steep because the base is constantly cleared; on a sub-aerially-dominated cliff, slumped debris often protects the toe and the profile slackens. Recognising which system a coastline represents is the key to explaining its profile and its retreat behaviour.
A wave-cut platform is more than a landform in its own right — it is the fossil record of cliff retreat. Each metre of platform width represents a metre of cliff that once stood there and has since been removed. Where the platform is wide (hundreds of metres at, for example, Robin Hood's Bay), it records prolonged retreat; where it is narrow or absent (granite coasts), it records minimal retreat. The platform's seaward gradient (typically 1–3°) and its width are themselves controlled by tidal range and wave energy: a large tidal range spreads erosion over a wider vertical band, tending to produce a gentler, wider platform, whereas a small tidal range concentrates erosion at one level. Reading a platform as a retreat archive is a sophisticated AO2 move that links form directly to the process history of the coast.
Where a coastline is composed of alternating bands of resistant and less resistant rock, differential erosion creates a pattern of headlands and bays.
Key Definition: Differential erosion is the selective erosion of rocks of varying resistance, producing an irregular coastline of headlands (resistant rock) and bays (less resistant rock).
Headlands and bays are not static; they participate in an elegant feedback that changes over time. Once differential erosion has cut a bay, wave refraction (Lesson 2) bends incoming crests so that energy converges on the projecting headland and diverges across the bay. This is initially a positive relationship for the contrast — the headland, now bearing concentrated energy, develops the high-energy micro-landforms (caves, arches, stacks), while the bay, in its energy shadow, accumulates a protective beach. But over the longer term the same feedback becomes negative at the landscape scale: by concentrating erosion on the headland, refraction gradually trims it back, while the sheltered bay, protected by its growing beach, erodes ever more slowly. The net effect over millennia is a reduction in the contrast — the coast tends to straighten toward a smoother, more even planform in which wave energy is distributed more uniformly. The headland-bay coast is therefore a transient configuration on the way to an equilibrium form, and the stage a given coast has reached (sharply indented and youthful, or gently curved and mature) can be read from its planform. This temporal reading — landforms as stages in an evolving system rather than fixed objects — is precisely the analytical sophistication that distinguishes top-band landform answers.
This is one of the most frequently examined landform sequences at A-Level. It represents the progressive erosion of a headland through a predictable series of stages.
graph TD
A["Headland exposed to wave attack on three sides"] --> B["Weakness (joint/fault/bedding plane) exploited by hydraulic action and abrasion"]
B --> C["CAVE: deep recess eroded into cliff face"]
C --> D["Caves eroded on both sides of headland meet"]
D --> E["ARCH: opening right through the headland"]
E --> F["Arch roof widened and weakened by weathering and erosion"]
F --> G["Roof collapses — seaward portion isolated"]
G --> H["STACK: isolated pillar of rock"]
H --> I["Stack eroded at base; undermined"]
I --> J["STUMP: low remnant visible at low tide"]
Cave formation: Waves attack a zone of weakness in the headland — typically a joint, fault or bedding plane. Hydraulic action forces water and compressed air into the crack, progressively enlarging it. Abrasion by sediment-laden waves scours the walls and floor. Chemical solution may also contribute where the rock is soluble. The cave deepens as the back wall is eroded, forming a recess that can extend tens of metres into the headland.
Arch formation: Where caves on opposite sides of a narrow headland erode far enough to meet, a natural arch is created. The arch has a roof of rock spanning the gap, supported by pillars on either side. The roof is subjected to intense weathering from above (freeze-thaw, salt crystallisation, root action) and erosion from below (wave impact on the underside).
Stack formation: Eventually, the arch roof becomes too thin and weak to support itself. It collapses, leaving an isolated pillar of rock — a stack — separated from the headland. The stack continues to be eroded at its base by wave action.
Stump formation: Continued erosion at the base of the stack causes it to collapse, leaving a low remnant called a stump (or skerry), which may only be visible at low tide.
It is worth stressing the structural control running through the whole sequence, because it is the most-rewarded analytical point. Every stage exploits a pre-existing line of weakness: the initial cave forms along a joint, fault or bedding plane, the arch breaches through where caves on opposite faces follow the same weakness, and the stack falls when the roof — already weakened along bedding planes — fails. This is why caves, arches and stacks are almost always aligned with the structural grain of the rock, and why the spacing and orientation of joints predicts where in a headland the sequence will develop. At Old Harry, the well-developed vertical joint network in the Cretaceous chalk provides abundant entry points, which is why this stretch produces such a clear sequence; on a massive, unjointed rock of the same lithology, the sequence would develop far more slowly or not at all. The landform sequence is therefore a collaboration between marine process (the agent) and rock structure (the template) — the integrating theme of Lesson 8 made concrete in a single headland.
Old Harry Rocks at Handfast Point on the Isle of Purbeck is the classic UK example of this landform sequence:
The Needles are three chalk stacks at the western tip of the Isle of Wight:
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