Coasts
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Powerpoint on Coasts for EDEXCEL A GCSE Geography

Powerpoint on Coasts for EDEXCEL A GCSE Geography

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Coasts Presentation Transcript

  • 1. Coasts Unit 2 Thursday 22nd May 2014
  • 2. Constructive Waves Characteristics Destructive Waves Characteristics Constructive and Destructive Waves Lower Longer Bigger swash than backwash Less than 10 per minute Steeper Shorter Bigger backwash than swash More than 10 per minute Creates a trough offshore
  • 3. Hydraulic Action
  • 4. Abrasion Caused by waves picking up stones and hurling them at the cliff face, wearing it away.
  • 5. Attrition Any material, but usually rocks and pebbles will become rounder and smaller over time as it collides with other rocks and pebbles.
  • 6. Corrosion The dissolving of rocks and minerals by sea water.
  • 7. Headland Bay
  • 8. Headlands and Bays Is all to do with geology! Geology = the type of rock Soft rocks get eroded quickly creating bays Hard rocks erode more slowly creating headlands
  • 9. Cliffs are steep rock faces along the coastline, they form along coastlines with resistant harder rocks such as chalk
  • 10. Wave-cut platforms are rocky ledges on the beach left behind after a cliff collapses. They become smooth over time with erosion.
  • 11. Cliff Retreat and Wave Cut Platforms 1) During times of high tide the waves attack the base of the cliff to form a wave cut notch. 2) As time passes corrosion and hydraulic action widen the notch causing the cliff to become undercut 3) Eventually the influence of gravity becomes too great and the cliff collapses. 4) This causes the cliff to retreat inland. 5) The rocks left at the base of the cliff are eroded by corrosion and abrasion until a smooth rocky platform is left, called a wave cut platform.
  • 12. Cave, Arch, Stack, Stump
  • 13. Weathering and Erosion Weathering – the breaking down of rock without any involvement of moving forces Erosion – the breaking down of rock by a moving force such as a wave
  • 14. Coastal Weathering Freeze Thaw Solution Biological Temperatures drop below freezing at night and then rise during the day Any water held in cracks in the rock freezes, expands and then thaws. This happens over and over until pieces break off. All rain is slightly acidic. Polluted air can be very acidic When rain falls on rocks, the acid reacts with some of the minerals causing them to dissolve The roots of vegetation grow into cracks in the rock. This splits the rock apart.
  • 15. Mass Movement • Bottom of the cliff eroded by waves and undercut • Rainfall saturates cliff and makes it heavier • Water trapped between layers of rock in the cliff acts like a lubricant • Rocks slide down cliff in a rotational manner • Often happens in clay • Rocks are weathered on the cliff face • They break loose and fall under the influence of gravity
  • 16. Clay Mass Movement - slumping
  • 17. Slumping Explained For slumping to occur soil must be on top of an impermeable rock such as clay (that is rock that does not allow water to soak into it. During times of heavy rainfall the soil above the clay can get saturated. At the same time waves undercut the base of the cliff. A layer of water builds up between the soil and the clay, where it cant sink it, lubricating it. Under the influence of gravity the soil slumps in layers down the cliff.
  • 18. Coastal Recession is affected by: Fetch – the bigger it is, the bigger the waves will be and the more the cliff will erode Geology – cliff recession is faster in soft rocks such as sand or clay, slower in hard rocks like chalk and limestone Coastal defences – if they protect the cliff, erosion will be less severe and the cliff will retreat more slowly.
  • 19. Coastal Flooding • Thames barrier protects London from flooding; closed during times of high tide and severe storms. • A series of new flood walls will also be installed in 2012 • The Environment Agency monitors the weather and tides 365 days a year and sends out warnings if coastal flooding is likely • People in Bangladesh build their houses on stilts to protect their properties from flooding • Also, the Coastal Embankment Project has led to the building of many flood walls, and 500 flood shelters have been built . • The local people are now being better educated about what to do in a flood and flood warning systems are being put in place
  • 20. Prevailing wind – the direction the wind blows from MOST OFTEN! In the UK our prevailing wind direction is from the South West. It is this that makes swash and Long shore Drift go onto the beach at an angle.
  • 21. Longshore Drift (LSD) 1) The waves approach the beach at an angle (in the UK it is 45o) depending on the direction of the prevailing wind. 2) The swash goes up the beach at the same angle carrying sediment and sand with it. 3) The backwash carries the sediment and sand back down the beach at 90o under the influence of gravity. 4) In this way sediment and sand is transported down the coastline.
  • 22. Coastal Engineering Hard engineering is anything that is man- made, usually out of concrete or wood Soft engineering is using anything that is already there in the landscape to try and manage the risk
  • 23. Hard Engineering – Sea Wall Pros • Strong • Long lasting • Reflects the wave energy and protects the base of the cliff • Cheap Cons • Looks ugly • Not popular with tourists
  • 24. Hard Engineering – Rip rap Pros • Strong • Long lasting • Absorbs wave energy and reducing erosion Cons • Not always pretty • Very expensive • Restricts access to the beach
  • 25. Hard Engineering – Revetments Pros • Absorbs wave energy and reducing erosion • Not too ugly • Cheap Cons • Has to be replaced quite often
  • 26. Hard Engineering – Off-shore Reefs Pros • Absorbs wave energy and builds up the beach • Not too ugly Cons • Very expensive • Unpopular with boats and fishing vessels
  • 27. Hard Engineering – Groynes Pros • Stop longshore drift and so build up the beach • Cheap • Popular with tourists Cons • Have to be replaced quite frequently • Do not stop erosion
  • 28. Soft Engineering – Beach Replenishment Pros • Builds up the beach again • Very popular in seaside resorts • Creates a natural barrier to erosion Cons • Has to be replaced quite frequently • Extremely expensive • Can make erosion worse at other places down the coast
  • 29. Soft Engineering – Cliff Regrading Pros • Reduces the risk of slumping • Looks natural • Cheap Cons • Does not stop erosion • Not guaranteed to work
  • 30. Soft Engineering – Managed Retreat Pros • Doesn’t cost anything • Very natural Cons • Loss of land and homes • Have to compensate people who loss their land
  • 31. Swanage • Managed due to weaknesses in the cliff and soft clays and the risk to houses and hotels on the cliff. • 90,000m3 of sand pumped onto the beach (beach replenishment) • 18 new groynes in 2005 to replace old timber ones • Cliff regrading and drainage to lower the risk of slumping • Cost £2.2 million in total