As wind blows over the sea's surface, friction is created producing a swell in the water. The energy of the wind causes the particles in the swell to rotate. The wave moves forward.
The size and energy of a wave is decided by:
- the length of time that the wind has been blowing for
- the strength and power of the wind
- how far the wave has travelled (called the fetch)
Waves can be destructive or constructive.
When a wave breaks onto the beach, 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.
Costal and river erosion
There a 4 types in which the sea erodes the coast:
- Hydraulic Action: This is the constant force of the sea crashing against the coast and river channel, air may get trapped in cracks and when the waves attack the coast pressure is created which may make the crack bigger
- Attrition: This is when rocks and pebblescrash against one and another. They are broken down to become smaller and smoother
- Abrasion: Rocks grind away the coast and river bed as the sea pushes them forward. It is like a sandpaper effect
- Solution: Acids contained in sea water will slowly dissolve certain types of rock such as chalk or limestone.
The sea transports sediment along the coast in 4 main ways:
- Traction: Large boulders and pebbles are rolled along the sea and river bed
- Saltration: Smaller rocks and pebbled are bounced along the sea and river bed
- Suspension: Small particles are carried along in the water, eg silts and clays. When large amounts of sediment are carried in suspension, it can make the water look cloudy
- Solution: Soluble minerals aredissolved in sea water and carried along in solution. The load is not visible
When a riverloses energy, it will drop or deposit some of the material it is carrying.
- Deposition may take place when a river enters an area of shallow water or when the volume of water decreases.
- Deposition is common towards theend of a river's journey, at the mouth.\
When the sea loses energy, it drops its load of sand, rock particles and pebbles, which it has been carrying. This is called deposition.
Deposition is likely to occur when:
- waves enter an area ofshallow water.
- waves enter a sheltered area, eg a cove or bay.
- there is little wind.