Coasts igcse geography
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  • 1. Introduction to coasts.  What is a coast: A coast is a zone where the land meets the sea.  Waves are the primary force causing erosion along coastlines. A wave is formed by the wind blowing across the surface of the water, creating ripples, which then grow into waves. As waves reach the coast the lower section slows due to friction. The upper section topples over and breaks forward.
  • 2. Explaining waves  The size of waves depends on:  The wind speed  The length of time during which the wind blows in the same direction.  The length of sea over which the wind blows. The greater these factors are the bigger the wave.
  • 3. Constructive waves  Constructive Waves have a number of important characteristics:  i) Their swash is much stronger than their backwash, causing the beach to be built up by the deposited material.  ii) They are less frequent, reaching shore between 6 and 8 times each minute.  iii) They are long waves and so roll onto the beach rather than crashing onto it.  iv) Constructive waves create a wide, gently sloping beach.
  • 4. Constructive waves
  • 5. Destructive Waves  Destructive Waves have a number of important characteristics:  i) Their backwash is much stronger than their swash, thus allowing them to remove material from the beach.  ii) They are frequent in number, usually between 10 and 15 per minute.  iii) They are tall waves, meaning they have a greater distance to fall when they break. This causes them to scour out the beach material.  iv) Destructive waves create a steep narrow beach
  • 6. Destructive Waves
  • 7. Processors of Erosion  1. Attrition:- “Rock on rock”- Particles carried by the waves crash against each other and are broken up into smaller particles. 2. Corrasion (also known as abrasion):- “Rock on cliff”- Particles carried by the waves crash against the cliffs, eroding the cliffs. 3. Corrosion:- “Rusting / dissolving”- Salt in the seawater slowly dissolves the cliffs. - The material produced is carried away by the process of solution. 4. Hydraulic Action:- “Pressuring”- The water traps air in cracks and caves in the rock. - This air is compressed by the incoming waves placing great pressure on the rocks, causing them to crack eventually.
  • 8. Long shore drift  Long shore Drift  - Material moved along the coastline by the waves.  - When waves approach the coast at an angle, carrying material with them. This is carried up on to the beach by the swash.  - The material is then dragged out to sea by the backwash, but this time it travels at right angles to the beach, as it will roll down the steepest gradient (gravity)  - This movement will slowly transport material laterally along the coast.
  • 9. Long shore drift
  • 10. Sediment movement, transportation.  i) Traction – the rolling of large material along the sea floor by the waves.  ii) Saltation – the bouncing of slightly lighter material along the sea floor.  iii) Suspension – Small particles of material carried by the water.  iv) Solution – Material is dissolved and carried by the water.
  • 11. Marine Transpiration
  • 12. Headlands and bays
  • 13. Headlands and Bays  A headland: 1. Orojects out into the sea 2. Is usually longer than its bredth (width) 3. Has sides which form cliffs  A bay: 1. has a semi – circular shape of sea extending into the land 2. A wide, open entrance from the sea. 3. Land behind it that Is lower than the headlands on either side.
  • 14. Cliffs and wave cut platforms  Cliffs are formed when destructive waves attack the bottom of the rock face between high and low water mark.  - The area under attack is eroded using the major processes of coastal erosion.  - Points of weakness, such as faults and joints are attacked most, and eventually a wave-cut notch is gouged out.  - The rock above overhangs the notch, and as it is cut deeper into the rock, gravity causes the arch rock to collapse.  - The loose rocks are removed by the sea and transported along the coast by long shore drift.  - The whole process of undercutting the cliff begins again.  - As the cliff is eroded backwards it leaves behind a wave-cut platform, at the level of the low water mark.  - This platform is rarely eroded, as the waves energy is concentrated on eroding the area between the high and low water mark, and not the rock that is underneath them.
  • 15. How cliffs are formed
  • 16. How caves arches and stacks are formed  - Mainly seen on headlands.  - Waves start by attacking the main points of weakness in the rock: the joints and faults.  - A point of weakness is increased in size until it becomes a cave.  - The waves continue to attack the cave, which finally results in an arch being formed through the headland.  - The arch is attacked both by coastal erosion and sub- aerial erosion and finally the roof of the arch falls into the sea.  - This leaves behind a stack, which is then slowly eroded down to become a stump.
  • 17. How caves, arches and stacks are formed
  • 18. How spits are created
  • 19. Spits and bars  - A long, narrow ridge of sand attached at one end to the coast.  - Built up by long shore drift transporting material along the coast.  - At a bend or break (for an estuary) in the coastline the material being carried is dropped. (move from high energy to low energy environment) The material builds up away from the coastline.  - As the spit builds out to sea the end is affected more by the wind and by wave currents, causing the end to curve towards the shore, to create a hook end.  - Material often accumulates in the area of standing water that occurs behind a spit, and this can lead to the formation of salt marshes.  - Spits can be areas where large sand dunes build up, nearer the back of it.  If the spit extends across a bay it is called a bar.
  • 20. Coral Reefs  Are mainly in the pacific ocean in shallow warn seas (26-7degrees)  Coral is made of Calcium carbonate(like limestone)  Zooaxanthallae lives inside coral and does lots of important jobs such as absorbing CO2, releasing CO2 and making food for Polyps.  There are different types of coral such as fire coral, plate coral, brain coral etc.  Coral reefs are important to us because they give us protection from wave breakage, make jobs, food(fishing) and climate change (absorb CO2)
  • 21. Case study – Holderness  Location  Eastern side of the UK  East Yorkshire  Facing the North Sea  3Km south of Hornsea  Description  · Mostly consists of cliffs up to 30 metres high  · At the Humber estuary there is a spit called Spurn Head  · Cliffs have been retreated at a rate of about 1.2 metres a year
  • 22. Holderness – continued  Causes of Erosion  · Cliffs made of soft material (mainly clays and sands) that is easily undermined by wave action  Water logging of the cliffs by rain results in slumping  Attacked by destructive waves that are blown by strong winds across the North Sea  Processes of hydraulic action and abrasion at work  · Sand at the foot of the cliffs is constantly moving south due to longshore drift. This means a wide beach cannot be created so the cliff is relatively unprotected
  • 23. Holderness - Continued  Effects of Erosion  · 4km stretch of land has been lost to the sea since Roman Times  · Villages, farms (e.g. Grange Farm at Great Cowden) and caravan sites lost to the sea  · Easington gas terminal is at risk of falling into the sea  · Towns including Hornsea and Withernsea are under threat  · Main roads at risk including the B1242 at Mappleton  Protection Techniques   ·Wooden revetments and rock barriers have been constructed to protect Mappleton  · A series of groynes have been constructed at the cliff base to prevent the movement of beachmaterial  However a large rock groyne at Mapleton has increased erosion to the south to Arate of 10 metres per year by blocking the movement of protective material  · A 1km sea wall costing £4.5 million has been built to protect Easington gas terminal  · Concrete blocks and rubble have been dumped at the cliff base as a temporary barrier to absorb wave energy  · Proposal to dump colliery waste 50km from the coast to refract waves and encourage the formation of bays that would hold sand