Transcript Slide 1
Coastal Processes - Creating waves - Constructive waves - Destructive waves - Processes of erosion - Processes of transportation - Longshore drift - Summary Creating waves Waves are created when the wind blows across the surface of the sea. The friction between the wind and the water pushes the water up into waves. The height and power of a wave depends on two factors: • the distance it has had to travel across open water to reach the coastline • the wind speed. If waves have had to travel across a large area of open water, then they will have had time to gather energy and will have reached their full height. The length of the water over which the wind has blown is called the FETCH. Greater fetch + strong wind = more powerful wave with greater potential for erosion Constructive waves have three main features: • They are low in proportion to their length • They have a strong swash which carries material up the beach and and a weak backwash which doesn’t take the material away • They break gently, with only six and nine waves per minute Constructive waves allow material to be deposited along the coastline and form features such as spits, tombolos and bars Destructive waves have three main features: • They are high in proportion to their length • The backwash is much stronger than the swash so that rocks, pebbles and sand are carried back to the sea • They are frequent waves, breaking at an average rate of between eleven and fifteen per minute Destructive waves erode the coastline and help form features such as wave cut platforms, headlands, bays, arches, stacks, caves and stumps Processes of erosion: HYDRAULIC ACTION: Hydraulic action results from the weight of water hitting the coast. Air trapped in cracks is suddenly compressed by the breaking waves, which increases the pressure on the rocks. This type of erosion is greatest in storm conditions. CORRASION (also called Abrasion ): Breaking waves throw sand and pebbles against the cliff face which scrape away at the rock. This can cause undercutting at the base of a cliff. ATTRITION: Particles are reduced in size as they collide with the rock face and with each other in the breaking waves. They become smaller and more rounded. CORROSION (also called solution): This is the dissolving action of sea water on the rocks and it is most effective on limestone rocks. PROCESSES OF TRANSPORTATION Traction: This is when rocks and heavy boulders are dragged along the sea bed. This would usually occur when the waves do not have enough energy to carry the material Saltation: This is when smaller boulders are bounced along the sea bed Suspension: Material such as sand grains, are carried along in the water in suspension Solution: Lime from chalk and limestone rocks dissolves and is carried in solution Longshore drift: The transport of sand and pebbles along the coast is called LONGSHORE DRIFT Waves often approach the coast at an angle and the swash carries the sand and pebbles up the beach at the same angle. The backwash, however carries the material back down the beach at right angles as this is the steepest gradient. This causes the material to move along the coastline in a zig-zag motion and the material will eventually be deposited when the waves lose energy. The general direction of longshore drift is decided by the prevailing wind direction. SUMMARY -Constructive waves have a strong swash and a weak backwash so therefore deposit material on the coastline - Destructive waves have a weak swash and a strong backwash so therefore erode material from the coastline - The distance over the sea that the wind has blown when creating waves, is called the FETCH - The four types of erosion are hydraulic action, corrasion, corrosion and attrition - The four types of transportation are saltation, traction, solution and suspension - Material can also be transported along the coast in the zig-zag movement called longshore drift