How do waves erode headlands and build beaches and spits along a coastline?
The formation of coastal features of erosion - headlands and bays, cliffs, caves, arches and stacks - and of deposition - beaches, spits and sand bars - by wave action and longshore drift.
An SQA National 5 Geography answer on coastal landscapes, explaining how wave erosion forms headlands, bays, cliffs, caves, arches and stacks, and how deposition and longshore drift form beaches, spits and sand bars, with named UK examples.
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What this dot point is asking
The SQA wants you to explain how the sea shapes the coast: how wave erosion creates headlands and bays, cliffs, caves, arches and stacks, and how the movement and deposition of material by waves and longshore drift create beaches, spits and sand bars. You should support an answer with a labelled diagram and a named example.
How waves erode
Waves use three main erosion processes:
Headlands and bays
Where bands of hard and soft rock meet the coast, the softer rock (such as clay) is eroded faster to form a curved inlet called a bay, while the harder rock (such as limestone) is left sticking out into the sea as a headland. Waves then concentrate their energy on the exposed headlands.
Cliffs and wave-cut platforms
Waves erode the base of a headland between high and low tide, cutting a wave-cut notch. As the notch deepens, the rock above is undercut and collapses, so the cliff retreats inland. The flat, rocky area left behind at the base, exposed at low tide, is a wave-cut platform.
Caves, arches, stacks and stumps
On a headland the sequence is:
- Waves attack a crack or line of weakness by hydraulic action and abrasion, widening it into a cave.
- The cave is eroded right through the headland to form an arch.
- The arch roof is undercut and weakened until it collapses, leaving an isolated pillar called a stack.
- The stack is undercut over time and collapses to a lower stump.
A famous Scottish example is the Old Man of Hoy, a sea stack in Orkney.
Deposition: beaches, spits and bars
Where waves lose energy, they drop (deposit) the sand and shingle they carry.
- A beach is built where sand and shingle are deposited, usually in the sheltered water of a bay.
- A spit forms where the coast changes direction (at a river mouth or bay): longshore drift carries material out into the open water, building a long ridge that may curve into a hook, with salt marsh forming behind it (for example Spurn Head).
- A sand bar forms when a spit grows right across a bay, joining two headlands and trapping a lagoon behind it.
Examples in context
Example 1. Orkney's Old Man of Hoy. This 137 m sea stack stands off a cliff of layered sandstone, formed after an arch in the headland collapsed, a textbook stack used in coastal teaching.
Example 2. Spurn Head, Yorkshire. A long curved spit built by longshore drift carrying material south down the coast and depositing it where the Humber estuary changes the coastline direction.
Try this
Q1. Name the process that moves sand and shingle along a coastline. [1 mark]
- Cue. Longshore drift.
Q2. State the feature left when the roof of an arch collapses. [1 mark]
- Cue. A stack.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style5 marksExplain the formation of a stack. You may use a diagram or diagrams.Show worked answer →
A 5-mark "Explain the formation" answer rewards a clear sequence, so trace the feature from crack to stack and name the processes.
Waves attack a line of weakness in a headland by hydraulic action (the force of water compressing air in cracks) and abrasion (rocks thrown at the cliff), widening the crack into a cave.
Erosion continues until the cave is cut right through the headland to form an arch.
The roof of the arch is undercut and weakened by continued erosion and weathering, until it can no longer support itself and collapses.
This leaves an isolated pillar of rock standing away from the headland called a stack. Over time the stack is undercut and collapses to leave a lower stump.
Markers reward the ordered sequence (crack, cave, arch, stack, stump) with the processes named (hydraulic action, abrasion). A labelled diagram can score marks.
SQA N5 style4 marksExplain how a spit is formed.Show worked answer →
This needs the process of longshore drift built up step by step, so each mark is a developed point.
Waves approach the beach at an angle because of the prevailing wind, carrying sand and shingle up the beach in the same direction (swash).
The backwash drags the material straight back down the beach under gravity, so over many waves material moves along the coast in a zig-zag. This is longshore drift.
Where the coastline changes direction, such as at a river mouth or bay, the material is deposited in the sheltered water and builds out into a long ridge of sand and shingle called a spit.
A change in wind direction can curve the end of the spit into a hook, and salt marsh forms in the sheltered water behind it. Markers reward naming and explaining longshore drift, the role of a change in coastline, and the deposition that builds the spit.
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Sources & how we know this
- National 5 Geography Course Specification (C833 75) — SQA (2025)
- National 5 Geography - Course overview and resources — SQA (2025)