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Coastal Landscapes & Processes:

There are two types of Waves, Destructive and Constructive:

Destructive waves have high wave energy and are mainly responsible for erosional processes and take sediment away from coastlines/beaches towards the sea. They have a high wave frequency of over 10 waves per minute; also, they have a stronger backwash compared to the swash. Furthermore, they are powerful and have a tall wave crest of over 1 meter. 

Constructive waves are accountable for deposition. They obtain a low wave height of under 1 meter and have low wave energy. In addition, they have the opposite process of destructive waves; they work from swash to backwash and in this case the swash is stronger than the backwash. In other words, they push sediment up the beach.

 

Types of Coastal Weathering:

• Physical Weathering – When spray from waves lands on rocks, the water can evaporate leaving the salt behind. Salt crystals grow and create stresses in the rock, causing it to break into small fragments, e.g. freeze-thaw and exfoliation

• Chemical Weathering – When the air is polluted and it is very acidic, therefore, when it rains and the acidic rain collides with the minerals, its reaction cause the rock to dissolve and the rock to decay

• Biological weathering – The roots of vegetation goes through the cracks widening it and then making it fall apart

Types of Wave Erosions:

• Hydraulic action – This results from waves hitting cliffs, forcing air pockets into the cracks

• Abrasion/Corrasion –The pebbles picked up from the waves are flung against the cliff face wearing the cliff away.

• Attrition – Pebbles by the waves collide with other particles and become rounder

• Corrosion/Solution – The dissolving of rocks and minerals by water

Types of Coastal Mass Movement:

• Rock fall – Fragments of weathered rock fall from a cliff under gravity and collect at the base

• Slumping - Happens when the bottom of a cliff is eroded by waves. The cliff slides downwards, often triggered by saturation due to rain, which both ‘lubricates’ the rock and makes it heavier

 

Landforms from Weathering, Erosion and Mass Movement:

Cliffs and Wave Cut Platforms:

A wave cut platform is formed when a destructive wave hits the cliff face, causing a weakening between the lower and higher water marks. Then, erosional processes such as abrasion and hydraulic action cause the rocks to crack and fall off and due to this process; the cliffs have a weaker bottom half. Since it is not supported by gravity, a gravitational pull drags the rocks down. This process is named as a cliff retreat/recession. At this point the rock extend the wave cut notch and wave cut platform. This process carries on until the cliff is further away from the destructive waves to collide into it.

 

Headlands and Bays:

The key to the formation of headlands and bays is the differences in the geology. A typical form of a headland and bay is soft clay sandwiched in between hard limestone, or instead of limestone; chalk.  Erosional processes such as corrosion erode the soft rocks such as clay, sand and gravel and create bays, whereas the harder rocks; the headlands, take time to erode, leaving them sticking out in the sea.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Caves, Arches Stacks and Stumps:

Caves, arches stacks and stumps are created/sourced from a joint or a fault. Generally, a cave is formed because of erosional processes such as hydraulic action and abrasion eroding away the fault. Eventually, the cave is widened and deepened by further erosion. Then, the sea cuts through the whole cave and generates an arch, after that the sea widens the base leaving the roof unsupported. The roof of the arch is weakened via physical and biological weathering, thus leading the roof of the arch to collapsing – (part of the former cliff is now isolated and is called a stack). Overtime, the stack is undercut and breaks down; - and now all that remains is the stump. However, the stump has been eroded too much and so it is beach material through attrition.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Coastal Transport – Longshore Drift:

Longshore drift is the transportation of sediment from point A to B. The prevailing wind influences the direction in which the fetch constructively swashes. When it reaches the coastline the sediment moves back and down with the weak backwash at a 90-degree angle adjacent to the coastline, (zig-zag). When the wave bank is carried away, this process is carried on until the sediment collides with a coastline at which point the sediment is deposited. However, if a groyne is in the way of the swash, the sediment is deposited at that position because the wave cannot go further; despite of the sediment being deposited, the wave carries on with another process of longshore drift.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Depositional Landforms:

Beaches – Beaches are formed in sheltered environments, when sediment is deposited on coastlines and lead to the formation of beaches. When the swash is stronger than the backwash, deposition occurs. Sometimes sand from offshore bars can be blown onto the shore by strong winds. This is especially the case on coastlines that are sheltered from wind and waves, such as in the bay.

Example: Sometimes sand dunes may form – such as at Studland on the Dorset Coast.

Spit – A spit is the accumulation of sand with one end attached to the land and the other reaching out across as estuary or into the sea. Longshore drift carries sediment along the beach. When the coastline suddenly changes direction, possibly due to a river estuary, the beach material is deposited and builds up. Overtime, this deposition leads to the formation of a sand bank that extends the beach out into open water. This sand bank is known as a ‘spit’. The end of the spit often becomes curved because of strong winds and waves. Instantaneously, this spit generates a calm area of water behind it. A spit formation is likely to occur where: -

• Waves enter an area of shallow water

• Waves enter a sheltered area

• There is a little wind

• There is a good supply of material, (from longshore drift)

Bar – If a spit joins one part of the mainland to another, it is called a bar.

Example: There is a bar at Orford Ness in Devon.

Tombolo – Where a spit stretches to an island, joining it to coastline, the feature created is called a tombolo.