H Geography - Physical Unit - Lithosphere - Coastal Features

What are the four coastal erosional processes?

The four coastal erosional processes are;

• Hydraulic action

• Abrasion

• Attrition

• Solution

Hydraulic action in coastal erosion

Hydraulic action in coastal erosion is when pounding waves compress trapped air into the rocks creating an explosive blast which weakens and loosens rock fragments

Abrasion in coastal erosion

Abrasion in coastal erosion is when rock fragments are thrown against the rock, breaking down the cliff face and wearing away the rock

Attrition in coastal erosion

Attrition in coastal erosion is when rock fragments are slowly ground down by friction from wave action into smaller and rounder pieces which can then be used as abrasive material.

Solution in coastal erosion

Solution in coastal erosion is when carbonic acids and salts dissolve rock

How many coastal erosional features are there?

There are three coastal erosional features

What are the three coastal erosional features?

The three coastal erosional features are;

• Headlands and bays

• Caves, arches, and stacks

• Cliff recession and wave cut platform

Headlands and bays

• Headlands and bays form along discordant coastlines, this is when alternating bands of rock do not run parallel to the sea.

• The alternating bands of rock are hard and soft. An example of hard rock is chalk, an example of soft rock is clay. When the alternating bands are eroded it is known as differential erosion.

• A headland is an area of hard rock which juts out into the water. A bay is a sheltered area of soft rock in between headlands.

• Constructive waves build a small beach in the sheltered bay between the headlands.

• An example of a headland and bay is Swanage Bay.

• + Coastal erosional processes

Caves, arches, and stacks

• Rocks contain weak points that are more easily eroded. Over time, lines of weakness are enlarged and develop into small sea caves.

• In some cases, a blowhole can even form in the roof of the cave. As compressed air is pushed upwards by the power of the waves, vertical erosion occurs.

• There may be erosion on both sides of the headland, due to wave refraction until eventually the sea cuts through the back walls of the cave. This forms an arch.

• Continued erosion enlarges the arch. The base of the arch is also undercut by erosion, causing the arch to become unsupported.

• Eventually the arch collapses to form a stack, which is separated from the headland.

• An example of a stack is Old Harry in Dorset.

• + Coastal erosional processes

Cliff recession and wave cut platform

• Cliffs form where there is harder more resistant rock, such as granite or chalk, in contact with the sea.

• Wave energy is at its greatest when a steep high wave breaks at the foot of the cliff. Continued erosion causes the notch to become larger over time.

• Weaknesses such as joints, cracks, or faults in cliffs are undercut to form a wave cut notch. The rock above overhangs over the notch and as erosion continues the notch enlarges until the unsupported overhang collapses due to the weight.

• The new cliff face is then eroded and over time the cliff retreats inland. This leaves a gently sloping rocky surface called a wave cut platform which extends out to sea and away from the cliff.

• The platform is abraded by rock materials, with rock pools and pot holes forming. These are evident at low tide.

• An example of a cliff is Seacombe cliff.

• + Coastal erosional processes

How many coastal depositional processes are there?

There is one coastal depositional process

What is the coastal depositional process?

The coastal depositional process is longshore drift

Longshore drift

• Swash is where waves push material up the beach at an angle due to the prevailing wind

• The returning backwash is dragged down the beach at a right angle due to gravity

How many coastal depositional features are there?

There are three coastal depositional features

What are the three coastal depositional features

The three coastal depositional features are;

• Sandspit and saltmarsh

• Sandbar and lagoon

• Tombolo

Sandspit and saltmarsh

• Spits are low ridges of beach material that partly extend across a bay or estuary.

• Spits form when there is a change in direction on a coastline, allowing a sheltered area for deposition.

• Material slowly builds up to appear above the water.

• The spit develops as long as the supply of deposits is greater than the amount of erosion.

• The shape can become hooked or curved at the end in response to changes in wind direction or currents

• A salt marsh may form in a sheltered area behind a sand spit.

• An example of a sand spit and saltmarsh is Sandbanks in Poole

• + Longshore drift

Sandbar and lagoon

• Sandbars are low ridges of beach material that fully extend across a bay.

• Bars form when there is a change in direction on a coastline allowing a sheltered area for deposition.

• Material slowly builds up to appear above the water.

• The bar develops as long as the supply of deposits is greater than the amount of erosion

• If a spit reaches the other side of a bay then a sand bar is formed, this happens when there is no strong flow of water from a river to the sea.

• This encloses a sheltered lagoon behind it. Over time, this lagoon may dry up and infill with deposition.

• An example of a sandbar and lagoon is Chesil Beach and Fleet Lagoon

• + Longshore drift

Tombolo formation

• Tombolos are low ridges of beach material that connect the mainland to an island.

• They form where the coastline changes direction and where there is shallow water and a nearby island.

• The level of sand will be built up until it is eventually above sea level.

• The tombolo develops as long as the supply of deposits is greater than the amount of erosion

• It can be covered during high tide but it is possible to walk across to the island during low tide.

• An example of a tombolo is St. Ninian’s Isle Tombolo

• + Longshore drift