Sources of coastal energy and sediment; marine, sub-aerial and biological processes; erosional and depositional landforms; and the landforms produced by changing sea levels.

What this dot point is asking

AQA section 3.1.3 wants you to explain how coastal landscapes develop: the sources of energy and sediment, the marine, sub-aerial and biological processes that operate, the erosional and depositional landforms they create, and the landforms produced by sea-level change. The skill examiners reward is linking a named process to a named landform, ideally with a located example.

Sources of energy and sediment

The energy that shapes coasts comes from waves, generated by wind blowing over the fetch. Constructive waves (low, long, spilling) have a strong swash and build beaches; destructive waves (high, steep, plunging) have a strong backwash and erode them. Tides set the vertical range over which processes act, and currents redistribute sediment. Sediment is supplied by rivers, cliff erosion, longshore drift from adjacent coasts and offshore sources, and is balanced within a sediment cell (the sediment budget).

Marine, sub-aerial and biological processes

Marine erosion works by hydraulic action (compressed air and water in joints), abrasion (sediment hurled at the cliff), attrition (particles rounding each other) and solution (dissolving carbonate rock). Sediment is transported by traction, saltation, suspension and solution, and along the coast by longshore drift, driven by the dominant wave approach. Deposition occurs where energy falls below the transport threshold. Sub-aerial processes prepare the cliff: mechanical weathering (freeze-thaw, salt crystallisation), chemical weathering (carbonation, oxidation) and mass movement (rockfall on resistant cliffs, rotational slumping on saturated clays). Biological action, such as marram grass trapping sand or molluscs boring rock, also shapes the coast.

Erosional and depositional landforms

On a discordant coast (bands at right angles to the sea), differential erosion forms headlands and bays. On a headland the sequence runs crack to cave to arch to stack to stump (Old Harry Rocks, Dorset). Wave attack cuts a notch, undercutting the cliff, which collapses and retreats, leaving a wave-cut platform. Concordant coasts (bands parallel to the sea) form coves where the sea breaches a resistant outer band (Lulworth Cove).

Depositional landforms form where the sediment budget is positive: beaches (swash- or drift-aligned), spits (Spurn Head, a curved ridge of sand or shingle growing across a river mouth), bars (sealing off a bay to form a lagoon), tombolos (Chesil Beach linking the Isle of Portland to the mainland), and vegetated sand dunes and salt marshes in sheltered settings.

Landforms of sea-level change

Sea level changes eustatically (a global change in ocean-water volume, for example as ice sheets melt) and isostatically (local vertical land movement, for example rebound after ice unloading). Falling relative sea level produces emergent landforms: raised beaches and abandoned (relict) cliffs. Rising relative sea level drowns the coast to produce submergent landforms: rias (drowned river valleys, V-shaped cross-section) and fjords (drowned glacial troughs, U-shaped, often with a shallow entrance threshold). These set the boundary conditions within which marine and sub-aerial processes then operate.

Try this

Q1. Describe how a wave-cut platform forms. [4 marks]

• Cue. Waves erode a notch at the cliff base; the cliff is undercut, collapses and retreats, leaving a gently sloping platform exposed at low tide.

Q2. Distinguish between a ria and a fjord. [3 marks]

• Cue. Both are submergent valleys drowned by rising sea level; a ria is a drowned river valley (V-shaped), a fjord a drowned glacial trough (U-shaped, often with an entrance threshold).

Q3. Explain how a spit forms. [4 marks]

• Cue. Longshore drift carries sediment along the coast; where the coastline changes direction or a river mouth interrupts it, sediment is deposited in open water, building a ridge that may curve (recurved) as wave direction changes.