Waves can be destructive or constructive.
When a wave breaks, water is washed up the beach - this is called the swash. Then the water runs back down the beach - this is called the backwash. 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.
- are created from big, strong waves when the wind is powerful and has been blowing for a long time.
- occur when wave energy is high and the wave has travelled over a long fetch.
- tend to erode the coast.
- have a stronger backwash than swash.
- have a short wave length and are high and steep.
- constructive waves are created in calm weather and are less powerful that destructive waves.
- break on the shore and deposit material, building up beaches.
- have a swash that is stronger than the backwash.
- have a long wavelength, a low height.
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.-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.