Coasts

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  • Created by: Aashini
  • Created on: 09-12-13 22:10

Weathering

Biological – The break up of rocks due to the action of plants and animals e.g. plants roots going into the cracks of rocks. 

Chemical – the break up of rock by a chemical reaction e.g. carbonation is when carbonic acid (formed by the water and the CO2 in the air) reacts with rocks, such as limestone, and dissolves them away. 

Mechanical weathering – the break up of rocks without a chemical change occurring. There are two main types of chemical weathering. 

Exfoliation – Because rocks are poor conductors of heat, only the outer layer is affected by temperature change. Heat causes it to expand; lower temperatures cause contraction. Repeated expansion and contraction cause the outer layer to be peeled away. 

Freeze-thaw action – water gets into the cracks in the rock. Because of sub-zero temperatures in the night, this water freezes into ice and expands, which puts pressure on the crack. In the day, the water melts and releases the pressure. Repeated cycles eventually cause parts of the rock to break off.

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Process of Erosion

Mass movement is when a lot of material is removed from the coastline at one time. It causes a large retreat in the coastline too. There are two types – slides and slumps. Slides are when material slides off the coast in a straight line. Slumps are when the material shifts at a rotation. 

Erosional processes 

Hydraulic action – the sheer impact of the waves cause air to be forced into the cracks of the rocks, which cause them to break off. 

Abrasion – eroded material carried in the waves grind against the cliff face, and this causes more material to be taken from the cliffs. 

Attrition – eroded material bang against each other, and become smaller in size. Their edges are also rounded. 

Solution – carbonic acid in seawater dissolves some types of rock e.g. limestone and chalk. 

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Types of Waves

Constructive waves 

 Low frequency (6-8 waves per minute) 

 Strong swash, weak backwash, which causes them to deposit material on the beach. 

 Low in height, and they are quite long. 

Destructive waves 

 High frequency (10-14 per minute) 

 Strong backwash, weak swash, which causes them to take material from the beach. 

 Caused by storms further out into the sea. 

 Long fetch 

 Tall waves, so they crash onto the beach with great force

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Wave cut platforms

These landforms may be found on any coastline, mainly where there are destructive waves. These waves cause undercutting on the cliffs, which creates a dent in the bottom of the cliff edge. This is called a wave-cut notch.

This gets deeper, and eventually, the rock which is over the undercut area becomes unstable and falls.

The material is then cleared, and the cycle repeats again. Repeated cycles then cause a sloped platform to occur, and this is called a wave-cut platform. It can only be seen in low tide. 

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Headlands and Bays

These landforms are found where there are rocks of different resistances present along the coastline. Differential erosion causes the less resistant rock to retreat much further than the more resistant rock. Eventually, this goes so far back that it is no longer affected by erosion anymore. A bay is formed – which is a gently sloping beach.

The more resistant rock sticks out, and these are known as headlands.

Wave refraction causes more erosion on these landforms. The cracks in the side of these get larger due to erosion (hydraulic action and corrosion), and eventually form a cave. Over time, the cave will go through the rock, and become an arch. The material on the top of the arch then falls, creating a stack which is separate from the headland. The stack will erode to form a stump, which can only be seen at low tide. This causes the headland to retreat. This is continually done until the coastline becomes level again, where the cycle restarts. 

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Processes of transportation

Traction – large rocks are rolled along the sea bed by the force of water. 

Saltation – smaller rocks are bounced along the sea bed by the force of the water. 

Suspension – smaller particles are carried with the water flow. 

Solution – Some particles dissolve in the water and are carried along, causing it to change colour. 

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Spits

Spits are formed when there is a change in direction in the coastline. They are formed by the process of longshore drift, which takes material and deposits it elsewhere along the coastline. When the coastline changes direction, deposition continues to happen in the same direction. The end of the spit is curved because of the direction of the prevailing wind. Eventually, the spit will get to a point where the flow of water outweighs the deposition, and the spit can extend no further out to sea. The sheltered area becomes a salt marsh, which is eventually colonized by plants. If the spit goes all the way across a bay, and joins two headlands together, the enclosed water area is known as a lagoon

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Causes of rising sea level

 Melting of the ice caps, as the world is getting hotter. More volume of water is added to the sea, therefore the sea level rises. 

 Heating of oceans – if they are hotter, the particles take up more space, and sea levels rise. 

The rising sea level increases the chance of coastal flooding

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Impacts of coastal flooding

Economic, Social, Environmental, Political

 Loss of tourism and industry 

 Expensive to repair damage 

 Loss of agricultural land – sea water contains lots of salt, which makes land infertile.   

 People have died because of flooding. 

 Loss of jobs. 

 Loss of housing. 

 Water supplies can be contaminated with salt and sewage. 

 Increased erosion. 

 Damage to ecosystems. 

 Vegetation killed because force of water can uproot them. 

 Governments have to make policies to reduce future flooding. They could build better flood defences. 

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Coastal management strategies

Hard Engineering 

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Coastal management strategies

Soft Engineering 

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