Coasts are shaped by the sea and the action of waves. The processes that take place are erosion, transportation and deposition.
The size and energy of a wave is influenced by:
how long the wind has been blowing
the strength of the wind
how far the wave has travelled (the fetch)
When a wave breaks, water is washed up the beach
After the swash the water runs back down the beach
Constructive and destructive waves
With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash.
· Destructive waves are created in storm conditions.
· They are created from big, strong waves when the wind is powerful and has been blowing for a long time.
· They occur when wave energy is high and the wave has travelled over a long fetch.
· They tend to erode the coast.
· They have a stronger backwash than swash.
- · They are created in calm weather and are less powerful than destructive waves.
- · They break on the shore and deposit material, building up beaches.
- · They have a swash that is stronger than the backwash.
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. Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
- Abrasion. Bits of rock and sand in waves grind down cliff surfaces like sandpaper.
- Attrition. Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.
- Solution. Acids contained in sea water will dissolve some types of rock such as chalk or limestone.
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