How waves form:-
Waves are usually formed by the wind blowing over the sea. Friction with the surface of the water causes ripples to form and these to develop into waves. The stretch of open water over which the wind blows is called the fetch. The longer the fetch, the more powerful a wave can become. The winds are south westerly and come mainly from Brazil. The distance is has to travel is 10,000km (6000 miles).
What happens when waves approach the shore?
Types of waves
Associated with calm weather.
Associated with storm conditions.
Low in proportion to their length.
Tall in proportion to their length.
Less powerful waves.
Created when the wave energy is high and there is a large fetch.
Break on the shore and tend to deposit material.
Remove material from the coast and are therefore associated with erosion.
Responsible for transporting material.
Backwash is stronger than the swash.
Swash is stronger than backwash.
Arrive at >10 per minute.
Arrive at <10 per minute.
When waves break on a sandy or pebbly beach, the amount of backwash is often less than the amount of swash, why?
If the swash is stronger, the backwash is weaker.
The surface is permeable, so the water drains into the cracks, meaning not as much water will be washed back.
On a pebble beach, larger pebbles are often found bear the top of the beach, with smaller ones nearer the bottom, why?
The smaller pebbles are often found nearer the bottom of the beach because the backwash erodes the pebbles, making them smaller, and leaves them nearer the bottom. Also, when the waves bring up pebbles from the sea bed, they are often small, and the waves only have enough energy to deposit them nearer the bottom of the beach. Larger material at the top of the beach may originate from the top of the cliff.
The Coastal Zone
The coastline is shaped by a number of different processes. Processes which are directly the result of wave action e.g. the erosion, transportation and deposition of material in the coastal zone are known as marine processes. These marine processes are aided by the weathering of rocks exposed at the coast and mass movement.
Weathering is the disintegration or decay of rocks in their original place or close to the ground surface. As the name suggests, it is largely caused by elements of the weather such as rainfall and changes in temperature.
Mass movement is the downhill movement of material under the influence of gravity.
How does freeze-thaw weathering lead to cliff collapse?
When water gets into the joints and pores of the cliff it freezes overnight (freezes at 0°) this expands the joints and pores. As the temperature raises again, the ice melts, making the joints and pores contract. This is repeated and over a period of time, the cliff collapses, as the rocks tear away. This may cause rockfall. An example of this is ‘Beachy Head’ in East Sussex. A rockfall is a type of mass movement. ‘Beachy Head’ is a chalk cliff.
Weathering and mass movement provide an input of material to the coastal zone. Much of this is then carried away by the waves to be deposited elsewhere along the coast.
There are several processes of coastal erosion; coastal erosion is a marine process.
Hydraulic action – This involves the sheer power of the waves as they smash onto a…