Coastal erosion is caused by Destructive waves. Destructive waves are high waves with a strong back wash which breaks frequently. The strength of a wave depends on wind strength and fetch (distance over open water that the wave has travelled)
Coastal landforms creates by erosion include:Arches, caves, stacks, stumps wave cut plat forms, wave cut notches, headlands and bays
Factors influencing landforms include: rock type, soft rock is warn away easily and so rarely makes large caves. Rock structure eg many joints.
- Corrasion: (sometimes called abrasion): The wearing away of the rock caused by pebbles and material in the water smashing against the cliff face.
- Attrition: Stones or Pebbles smashing together in the water and breaking up into smaller pieces. Attrition material helps speed up Corrasion
- Hydraulic action: Water hitting the rocks compresses air in the rock joints causing the cracks to expand. When the water recedes the air rushes out and the cracks contracts. This alternate expansion and contraction breaks up the rock.
Formation of coastal Scenery
Formation of wave cut notch
1) Hydraulic action and Corrasion attacks the bottom of the cliff while weathering weakens the top.
2) The notch increases in size eventually causing the cliff to collapse
3) Wave backwash drags the rubble out to see creating a wave cut platfrom
4) The process repeats and the cliffs retreat
Formation of headlands and Bays
Headlands are formed when the sea attacks a section of the coast consisting of alternating bands of hard and soft rock. The bands of soft rock, such as sand or clay, erode quickly, while the bands of hard rock, such as chalk erode slowly. Leaving sections of the cliff jutting out. These are called headlands. The areas next to the headlands where the cliffs have eroded away are called bays
Formation of coastal Scenery 2
The formation of Caves, Arches, Stacks and Stumps
1) Cavesoccur from waves forcing their way into cracks in the cliff (hydraullic action) The water contains sand and other materials that grind away the rock (corrasion) until the cracks become caves.
2) If a cave is formed in a headland it may eventually break through the other side forming an Arch.
3) The Arch will eventually become bigger by erosion and weathing until it can no longer support the arch top. When the arch collapses it leaves a headland on one side and a column of rock, called a stack, on the other.
4) The stack will be eroded by hydraullic action and corrasion eventually collapsing to form a stump.
Deposition Costal Features
Despotion features are made of Constructive waves. Contructive waves are gently waves with a strong swash and a weak backwash.
Formation of Beaches
1) Beaches are made of eroded material that has been transported and deposited there by the sea.
2) The material found on a beach is often smaller nearer the shore and bigger near the cliffs, at the back of the beach. This is because waves break frequently near the shore line and so the material is broken down more effectively by attrition.
Sand-dunes: are formed if the prevailing wind is directed towards the land. The wind will blow the sand up the beach causing it to pile up
Tombolos: is a stretch of beach material that connects an island to the mainland.
Deposition Costal Features: Spits
Definition: A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end. Spits are usually formed where the prevailing wind blows at an angle to the coast line resulting in Long Shore drift.
Formation of a Spit
1) Spits form when Long shore drift is moving large amounts of sand and shingle along a coast which suddenly the direction of the coast changes, usually inwards.
2) The material however is still deposited and futher deposition of finer material enables the feature to build up to sea level.
3) During this time some of the material at the end of the spit may be pushed inland to form a curved end, a hook.
4) Waves cannot get past the spit, so the area between the land and the spit becomes a sheltered area where silt is deposited and mud flats or salt marshes form.
Coastal Management 1
Hard egineering options
Building a sea wall
- Advantages: protects the cliff base from erosion, can prevent flooding, protects buildings on cliffs
- Disadvantages: They are expensive to build and to maintain. The have a curved lip which defects waves and material away from the shore line however they waves still remain powerful and they may erode the wall.
Groynes -wooden barriers built at right angles to the beach
- Advantages: Prevents the movement of beach material along the beach (Long shore drift) Allows the build up of a beach, good for Tourism.
- Disadvantages: Can be unattractive, costly to build and maintain
Coastal Management 2
Boulder Barriers - large boulders piled up on the beach.
- Advantages: Absorb wave energy, allows build up of beach
- Disadvantage: can be expensive to obtain and transport boulders.
Coastal Management 2
Soft egineering options
Beach management -Replacing beach material that has been lost by erosion or long shore drift
- Advantages:Beaches are a natural defence against erosion and coastal flooding and are a good tourist attraction
- Disadvantages: While it can be inexpensive it does require constant maintenance
Managed Retreat - where the rest of the coast is allowed to erode and flood naturally, usually in places of low value
- Advantages: it encourages the developement of beaches and salt marshes and the cost is low
- Disadvantages: While it is a cheap option it is not free, some people with have to be copensated for loss of farm land or buildings.
Case Study: Holderness in Mappleton
Back ground information: The holderness coast is one of the most vunerable in the world retreating at one to two metres per a year. The . This is mainly because of strong prevailings winds and because the cliffs are made of soft boulder blay.village of Mappletone on top of the cliffs has approximately 50 properties
What was done?
- Two million pounds was spent on a coastal managment scheme
- Two rock groynes and a boulder rock armour was built at the bottom of the cliffs were built.
- Advantages: The settlement and cliffs of Mappleton are no longer at risk from erosion.
- Disadvantages: The groynes have stopped material moving along mappleton coast and therefore a beach has built up. However this has resulted in increased coastal erosion South Mappleton