Coastal Processes: Weathering, Erosion & Transportation Revision Notes | GCSE AQA Higher Geography

1. Why Coasts Are Constantly Changing

Stand at the base of a cliff and you are watching geology happen in real time. Waves crash, rocks crumble, and sediment travels kilometres along the shore — all driven by a set of physical processes that the AQA specification wants you to name, explain, and apply.

The coast is not shaped by one process alone. Rock type and rock structure determine how resistant a cliff face is, while weathering, erosion, mass movement, and transportation all work together — sometimes reinforcing each other — to sculpt the landforms you see on OS maps and in exam photographs.

2. Weathering at the Coast

Before waves can erode a cliff, the rock often needs to be weakened first. That weakening is done by weathering — the breakdown of rock in place, with no transport involved. At the coast, two types matter most: mechanical weathering and chemical weathering.

Picture a coastal cliff riddled with joints and bedding planes. Water from rain or sea spray seeps into those cracks. When overnight temperatures drop below freezing, that water expands and forces the crack wider. Over hundreds of cycles, the crack grows until a block of rock detaches — this loose material then becomes ammunition for wave erosion below.

Carbonation is slow but relentless. Chalk cliffs along the south coast of England are particularly vulnerable because chalk is almost pure calcium carbonate. The acid dissolves the cement holding grains together, weakening the rock long before a wave touches it. This is why rock type matters so much — a granite cliff resists chemical weathering far better than chalk.

3. Mass Movement: When Cliffs Collapse

Weathering weakens rock, but it is mass movement that brings it down. Mass movement is the downslope movement of material under gravity — and at the coast, it is one of the most dramatic ways a cliff retreats. The AQA specification names three types you must know: sliding, slumping, and rock falls.

Slumping is the most common form of mass movement on soft-rock coasts such as those made of clay or boulder clay. After heavy rainfall, the cliff material becomes saturated, heavier, and less cohesive. The material rotates along a curved slip plane, leaving a characteristic curved scar at the top and a slump lobe at the base. Holderness on the Yorkshire coast is a classic example, retreating at an average of around 2 metres per year partly because of repeated slumping.

Rock falls, by contrast, are associated with hard-rock coasts where freeze-thaw or wave undercutting detaches individual blocks. The blocks fall vertically or bounce down the cliff face, accumulating as a scree slope at the base — material that waves will then use as a tool for further erosion.

4. Wave Erosion: The Three Key Processes

Mass movement delivers loose material to the cliff base, but it is wave erosion that actively attacks the cliff itself. Waves are the primary agent of coastal erosion, and AQA requires you to know three specific processes: hydraulic power, abrasion, and attrition.

Think of hydraulic power as the wave using air as a battering ram. The more powerful the wave — and the more jointed the rock — the more effective this process becomes. Storm waves can exert pressures of over 30 tonnes per square metre on a cliff face, which is why cliff retreat accelerates dramatically during winter storms.

Abrasion is why the material produced by mass movement matters so much. Those fallen boulders and pebbles at the cliff base become the tools that waves use to erode the cliff further. A wave armed with coarse sediment cuts into rock far more effectively than a wave carrying only water — which is why beaches can actually protect cliffs by absorbing wave energy before it reaches the rock face.

Here is a distinction that catches many students out. Attrition acts on the sediment itself, not on the cliff. You can recognise its effect by looking at beach pebbles: angular fragments near a cliff source become progressively more rounded further along the coast, because they have been knocked against each other repeatedly during transport.

5. Transportation: Longshore Drift

Once erosion has produced sediment, that material does not stay put. Waves transport it along the coastline through a process called longshore drift — and understanding this process explains why beaches form where they do, and why coastal management structures like groynes are built.

Worked example: How Longshore Drift Works

Describe the sequence of events that moves sediment along a coastline by longshore drift.

1. Prevailing winds drive waves towards the shore at an oblique angle — typically from the south-west in the UK. — The angle of wave approach is determined by the prevailing wind direction. In the UK, the dominant south-westerly winds mean longshore drift generally moves sediment from west to east along the south coast.
2. The swash (the wave rushing up the beach) carries sediment diagonally up the beach in the same direction as the wave approach. — The sediment — sand, pebbles, shells — is pushed up the beach at the same oblique angle as the incoming wave. This is the 'forward' part of the zigzag.
3. The backwash (water draining back down the beach) moves sediment straight back down the beach at 90° to the shoreline, pulled directly downslope by gravity. — Gravity always pulls the backwash perpendicular to the shoreline, regardless of the original wave angle. This is the key asymmetry that produces net movement along the coast.
4. Each swash-backwash cycle moves sediment one step further along the beach in the direction of the prevailing wave approach. — Over thousands of cycles, sediment migrates progressively along the coastline in a zigzag path. The overall direction of movement is called the longshore drift direction.

Answer: Sediment is transported along the coast in a zigzag pattern: swash moves it diagonally up the beach at the wave angle, backwash returns it straight down under gravity, producing net movement in the direction of the prevailing wind and waves.

Longshore drift has significant consequences for coastal landforms. Where drift is interrupted — by a headland, a river mouth, or a human-built groyne — sediment accumulates and builds up features such as spits and beaches. Where drift removes sediment faster than erosion replaces it, beaches thin and cliffs become more exposed to wave attack.

6. Rock Type, Structure, and Coastal Landforms

All the processes covered so far — weathering, mass movement, erosion, and transportation — do not act on a uniform coastline. The rock type and rock structure of the coast determine how quickly and in what pattern these processes operate, and that variation is what produces the distinctive landforms you need to recognise and explain.

Rock type refers to the composition and hardness of the rock. Hard, resistant rocks such as granite and basalt erode slowly, producing bold headlands and steep cliffs. Soft rocks such as clay, sand, and chalk erode much more rapidly, retreating to form bays and low cliffs prone to slumping. Where hard and soft rock alternate along a coastline, differential erosion carves out a varied landscape of headlands and bays.

Rock structure refers to the arrangement of the rock — the orientation of bedding planes, joints, faults, and the angle at which rock strata meet the coast. A coastline where rock bands run parallel to the shore (called a concordant coastline) tends to be more uniform, with resistant rock forming a continuous barrier. Where rock bands run perpendicular to the shore (a discordant coastline), alternating hard and soft bands are exposed to wave attack, producing the classic headland-and-bay pattern.

Joints and bedding planes within the rock also matter at a smaller scale. Hydraulic power exploits existing joints, widening them into caves, arches, and eventually stacks. A rock with many closely spaced joints will erode faster than a rock of the same hardness but with fewer joints, because there are more entry points for wave pressure and chemical weathering.

7. Exam Technique: Getting the Marks

The processes in this lesson appear across a range of AQA command words. Knowing the content is only half the battle — you also need to match your answer style to what the examiner is asking for.

Every process covered in this lesson — from freeze-thaw weathering weakening a cliff, to hydraulic power exploiting its joints, to longshore drift carrying the resulting sediment along the shore — is part of one interconnected coastal system. Rock type and structure set the conditions; the physical processes do the work; and the landforms you see are the result.