Coasts are shaped by the sea and the action of waves.
The processes that take place are erosion,
transportation and deposition.
The action of waves
The power of waves is one of the most significant
forces of coastal change. Waves are created by wind
blowing over the surface of the sea.
The size and energy of a wave is influenced by:
• strength of wind
• how long the wind has been blowing
• How far the wave has travelled
Types of waves
Waves can be destructive or constructive.
• Constructive waves
– have limited energy;
– move material up the beach (deposition).
Types of waves
• Destructive waves
– larger and have more energy;
– tend to erode the coast;
– used by backwash to move material down the beach
The sea shapes the coastal landscape. Coastal
erosion is the wearing away and breaking up of rock
along the coast. Destructive waves erode the
coastline in a number of ways:
• Hydraulic action: as waves break against the cliff face, the
pressure of the breaking wave can compress air in cracks.
This compressed air gradually forces open the crack in the
rock - as this process continues, the rock becomes
• Corrasion: (also known as abrasion) rock fragments are
hurled at cliffs by breaking waves, gradually scraping away at
the cliff face.
• Attrition: rock fragments carried by the waves hit against
each other and gradually wear down to form sand and silt.
• Corrosion (also known as solution): occurs where the salt
water is able to dissolve some of the chemicals in rocks.
There are various sources of the material in the sea.
The material has been:
eroded from cliffs;
transported by longshore drift along the coastline;
brought inland from offshore by constructive waves;
carried to the coastline by rivers.
Waves can approach the coast at an angle because of
the direction of the prevailing wind. The swash of the
waves carries material up the beach at an angle. The
backwash then flows back to the sea in a straight line
at 90 degrees. This movement of material is called
Continual swash and backwash transports material
sideways along the coast. This movement of material
is called longshore drift and occurs in a zigzag.
Longshore drift is the process by which sand and
pebbles are moved along a beach by the movement
of the waves.
When the sea loses energy, it drops the sand, rock
particles and pebbles it has been carrying. This is
called deposition. Deposition happens when the
swash is stronger than the backwash and is
associated with constructive waves.