GCSE Geography | Erosion, Transportation and Deposition (Coastal Landscapes 3)

The processes of erosion, transportation and deposition play a huge role in shaping the coastline.

Erosion

This is the wearing away of rock. There are 4 specific processes that you need to know:

• Hydraulic action - this is where the force of the water erodes the rock. The waves pound the base of the cliffs forcing water into cracks. As the water goes into these rocks the air compresses, and as it leaves the pressure is suddenly released, which breaks down the rock from inside, with some of the rock coming off in large chunks
• Abrasion - this is where sand and shingle is hurled at the cliff base by the sea, which scratches and scrapes the rock, wearing it down. This occurs more in storm conditions
• Attrition - this is where the material being carried by the sea is worn down as pebbles and rocks collide with each other. This will wear away sharp edges over time to create rounded and smooth pebbles. The rocks may collide with such force that they can break into much smaller pieces
• Solution - this is where the chemicals in the water react with the minerals in the rock to dissolve them. This is particularly effective in certain rock types, e.g. limestone and chalk

The rate of erosion is higher when the waves reaching the coastline have a large fetch so the waves have time to build up, when there are strong winds, when the beach is not very wide so there is less material to absorb the wave's energy, where the rocks are soft so they are less resistant to erosion, and where the rocks have lots of joints, so they are weaker.

Transportation

This is the movement of material by the sea. The material carried by the sea is called load - and is usually material that has been eroded and picked up by waves. Load varies from large rocks to fine silt. There are 4 specific processes of transportation that you need to know:

• Traction - this is where large rocks and boulders are rolled along the sea floor
• Saltation - this is where small stones and pebbles are bounced along the sea floor
• Suspension - this is where light material is held in suspension just below the surface of the sea (suspended load)
• Solution - this is where minerals are dissolved in the water and tiny invisible particles are transported by the sea (not to be confused by the erosional process of solution!)

Longshore drift

Longshore drift is the movement of material along the coastline in a zig-zag fashion. Waves hit the coastline at an angle (the same direction as the wind), so the swash goes onto the beach at an oblique angle. Once the wave breaks the backwash returns to the sea at right angles to the coastline (due to gravity). This movement is repeated, transporting material from one end of the beach to the other (as in the diagram below).

Deposition

This is where waves lose their energy so drop the sediment load they were carrying. This adds sediment to the beach so builds it up. Deposition occurs when the sea is shallow and sheltered (e.g. in a bay or behind a spit), where there is a large source of sediment, where there is a large flat beach which causes the backwash to weaken due to friction, so it can't drag material out to sea, and when structures such as groynes trap sediment.