Coastal Landforms

Coastal landforms are the visible results of the processes you studied in the previous lesson. For the AQA GCSE exam, you need to know how each landform is created and be able to identify them on photographs and OS maps. This lesson covers both erosional and depositional landforms.

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Erosional Landforms

Erosional landforms are created where destructive waves and other processes wear away the coast. They are most commonly found on headlands and exposed coastlines made of resistant rock.

Headlands and Bays

When a coastline is made up of alternating bands of hard and soft rock, differential erosion occurs:

1. Soft rock (e.g., clay, sand) erodes more quickly, forming bays.
2. Hard rock (e.g., limestone, chalk) erodes more slowly, forming headlands that protrude out to sea.
3. Once headlands form, wave energy is concentrated on the headlands (wave refraction) and reduced in the bays, so bays become sheltered and accumulate beaches.

UK Example: The Dorset coast (part of the Jurassic Coast) shows excellent examples of headlands and bays. The Foreland (headland) is made of resistant chalk, while Swanage Bay has been eroded from softer sand and clay.

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Cliffs and Wave-Cut Platforms

Cliffs are the most common coastal erosional landform. They form through a repeating cycle:

1. Waves attack the base of the cliff by hydraulic action and abrasion, creating a wave-cut notch.
2. The notch deepens, undercutting the cliff above.
3. The unsupported rock above the notch eventually collapses due to gravity (mass movement).
4. The fallen debris is broken up and removed by waves.
5. The process repeats, and the cliff retreats inland.
6. The flat area of rock left behind at the base of the cliff is called a wave-cut platform.

Wave-cut platforms are gently sloping surfaces of bare rock, exposed at low tide. They can extend up to several hundred metres seaward.

Exam Tip: When describing cliff retreat on an OS map, look for the symbol for a cliff (short lines on the seaward side) and note whether there is a flat area between the cliff and the sea — this is the wave-cut platform.

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Caves, Arches, Stacks, and Stumps

This famous sequence of landforms develops on headlands through progressive erosion:

Stage	Landform	How it forms
1	Crack	Waves exploit a weakness (joint, fault, or bedding plane) in the rock by hydraulic action and abrasion.
2	Cave	The crack is enlarged into a hollow cave by continued erosion.
3	Arch	Two caves on opposite sides of a headland erode through to meet, forming an arch.
4	Stack	The roof of the arch collapses (weakened by weathering and wave attack), leaving an isolated pillar of rock — a stack.
5	Stump	The stack is eroded at its base and eventually collapses, leaving a low stump visible at low tide.

UK Example: Old Harry Rocks on the Dorset coast are a classic example of this sequence. The Old Harry stack stands next to Old Harry's Wife (a stump). A natural arch existed nearby until it collapsed in 1896.

UK Example: The Flamborough Head headland in Yorkshire shows caves, arches, and stacks formed in resistant chalk.

Exam Tip: The sequence "crack - cave - arch - stack - stump" is one of the most commonly examined topics in GCSE Geography. Practise drawing and labelling a diagram of this sequence, and always name a real UK example.

The following diagram summarises the sequence of coastal erosion forming these distinctive landforms:

graph LR
    A[Crack] --> B[Cave]
    B --> C[Arch]
    C --> D[Stack]
    D --> E[Stump]

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Geo and Blowhole

• A geo is a narrow, steep-sided inlet formed when the roof of a coastal cave collapses.
• A blowhole is a vertical hole that forms when a crack in the roof of a cave is enlarged by hydraulic pressure. When waves enter the cave, compressed air and water are forced up through the blowhole, sometimes creating a spray.

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Depositional Landforms

Depositional landforms are created where waves lose energy and deposit their load of sediment. They are most commonly found in sheltered bays, on low-energy coastlines, and where longshore drift moves sediment along the coast.

Beaches

A beach is an accumulation of sand, shingle, or pebbles deposited by constructive waves. Beaches vary in shape, size, and material:

Feature	Sandy Beach	Shingle/Pebble Beach
Material	Fine sand	Pebbles, cobbles, shingle
Gradient	Gentle slope	Steep slope
Width	Often wide	Often narrow
Formation	Constructive waves in sheltered areas	High-energy waves; larger material deposited
Features	Ripples, runnels, berms	Storm ridges (berms of coarse material thrown up by storm waves)

Key beach features:

• Berms — small ridges of material running parallel to the sea, marking the limit of swash at different tide levels.
• Storm ridge — a large berm of coarse material at the back of the beach, deposited during storms.
• Cusps — semi-circular hollows formed by a combination of swash and backwash patterns.

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Spits

A spit is a long, narrow ridge of sand or shingle that extends from the coastline into the sea or across an estuary. It forms where:

1. Longshore drift transports sediment along the coast.
2. The coastline changes direction (e.g., at a river mouth or estuary).
3. Sediment continues to be deposited in the original direction of longshore drift, building out into the open water.
4. The end of the spit often curves inward (a recurved tip or hook) due to wave refraction and changes in wind direction.
5. Sheltered water behind the spit becomes a low-energy environment where mud and silt are deposited, often forming a salt marsh.

UK Example: Spurn Head (or Spurn Point) is a 5.5 km spit at the mouth of the Humber Estuary in Yorkshire. It has been formed by longshore drift transporting material southward along the Holderness coast.

UK Example: Dawlish Warren in Devon is a sand spit that partially blocks the mouth of the River Exe.

Exam Tip: When describing spit formation, always explain the role of longshore drift, the change in coastline direction, and the formation of the recurved tip. Naming a real UK example will earn you extra marks.

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Bars and Lagoons

A bar forms when a spit grows across a bay, completely sealing it off from the sea. The water trapped behind the bar becomes a lagoon, which may eventually fill with sediment and become a freshwater lake or marsh.

UK Example: Slapton Ley in Devon is a freshwater lagoon behind a shingle bar called Slapton Sands.

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Tombolo

A tombolo is a bar that connects the mainland to an offshore island. It forms when sediment is deposited in the shallow water between the island and the coast.

UK Example: Chesil Beach in Dorset is a tombolo connecting the mainland to the Isle of Portland. It is approximately 29 km long and is made up of graded shingle (the pebbles increase in size from west to east).

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Sand Dunes

Sand dunes are mounds of sand formed by wind deposition above the high-tide mark. They develop in a sequence from the coast inland: