Coastal processes — waves, erosion, transportation, deposition

The coast is one of the most dynamic environments on Earth. CCEA examiners expect you to explain how different wave types cause different outcomes, and to describe the four types of coastal erosion and transportation (which mirror river processes but with important differences).

Wave types

Constructive waves (low energy):

• Long wavelength; low frequency (6-8 per minute).
• Gentle swash (water rushing up the beach) that is STRONGER than the backwash (water returning).
• Net effect: material is deposited on the beach → builds up landforms.
• Common on sheltered coasts (e.g. the south Antrim coast near Ballycastle on calm days).

Destructive waves (high energy):

• Short wavelength; high frequency (10-14 per minute).
• Powerful backwash that is STRONGER than the swash.
• Net effect: material is dragged away from the beach → erodes landforms.
• Common on exposed coastlines (e.g. the Giant's Causeway, north Antrim).

Coastal erosion — four processes (same names as river erosion)

Hydraulic action: powerful waves trap and compress air in cracks in cliffs, eventually blasting rock apart. Most effective at the base of cliffs during storms.

Abrasion (corrasion): waves hurl pebbles and sand at the cliff face, wearing it away. Creates smooth, rounded hollows.

Attrition: rock fragments carried by waves collide with each other and break into smaller, rounder pieces.

Solution (corrosion): sea water dissolves soluble minerals in rock, particularly limestone.

Longshore drift (transportation)

Waves usually approach the coast at an angle (driven by the prevailing wind). This creates a net movement of sediment along the coast:

1. Swash carries sediment up the beach at an angle (matching the wave approach).
2. Backwash carries sediment back straight down the beach under gravity.
3. Each cycle moves sediment slightly along the coast.

Longshore drift (or littoral drift) is the net result. In NI, the prevailing south-westerly winds mean longshore drift is generally from SW to NE along the north Antrim coast.

Deposition

Deposition occurs when wave energy decreases (sheltered bays, wave refraction around headlands, spits curling into more sheltered water). Fine sand is deposited first, coarser material takes longer to settle.