Coastal Processes

Page 1

Concordant and discordant coastlines

Geological structures at the coast play a large role in the type of landforms present.

Concordant coastlines have rocks that lie parallel to the coastline.

They typically have alternative bands of hard and soft rock running parallel to the coastline, with the hard rock acting as a barrier to erosion.

When the hard rock is eroded, the soft rock is then quickly eroded, posing danger to local infrastructure. This is the case with Lulworth Cove, Dorset.

Discordant coastlines have bands of rocks that lie perpendicular to the coast.

Alternating layers of hard and soft rock that run perpendicular to the coastline typically form headlands and bays.

Page 2

Transportation

There are four types of transportation in the sea, as shown on the above diagram.

Traction is the rolling of larger rocks along the sea floor.

Saltation is the hopping/bouncing of smaller rocks and pebbles across the sea floor.

Very small pieces of sediment are carried through suspension.

Solution carries dissolved minerals in the sea water.

Page 3

Longshore Drift

Longshore drift is the process by which sediment is moved along the coastline.

The angle and direction of this movement is determined by the direction of local prevailing winds. Prevailing winds control the swash of a wave.

The backwash will always take the quickest route back to the sea and will move perpendicular to the coastline.

The strength of the swash and backwash in this process will determine the type of wave, and the type of landform present.

Page 4

Types of waves

Destructive waves:

Stronger backwash and weaker swash

Break frequently - 10-15 per minute

Are high in proportion to their length

Generally found on steep beaches

Agent in coastal erosion

Constructive waves:

Stronger swash and weaker backwash

Break infrequently - fewer than 10 per minute

Are long in proportion to their height

Generally found on gently sloping beaches

Agent in coastal deposition

Page 5

Coastal Erosion:

There are four types of erosion that take place at coastal regions:

Abrasion - the force of sand and pebbles being thrown by the sea scraping away at rock

Attrition - the wearing away of rocks in the sea by hitting off one another

Hydraulic action - the wearing away of rocks by the force of the water, this can also occur through the compression of air in small gaps by water

Solution - the chemical breakdown of rock by seawater

Rocks can also be broken down by physical and chemical weathering processes

Page 6

How the UK climate affects erosion:

Seasonality

Affects the rate of erosion

In Winter, diurnal temperature fluctuations bring freeze-thaw weathering

Storms

The UK is susceptible to regular storms

Storm waves have higher energies and are powerful agents of erosion

This means constant repair of sea defenses is necessary

Prevailing winds

The prevailing wind for the UK is from the southwest

Areas such as Cornwall and Devon in particular are subject to winds that have traveled far across the Atlantic ocean

This leads to waves having a longer fetch, and thus, more power to erode the landscape