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Sec 3 - Lesson 1 Coasts
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Sec 3 - Lesson 1 Coasts Presentation Transcript

  • 1. Coast Recap
  • 2. Profile of coast
  • 3. Wave terminology
  • 4. Wave terminology
    • When wind blows across the sea and the ocean, it causes the water surface to rise and fall.
    • This rising and falling of the water surface form the waves.
  • 5. Wave energy
    • Wind is the most important factor in shaping the coastlines.
    • As wind blows from the sea to the land, it produces a lot of energy which is transferred to the waves as wave energy.
    • Wave energy id seen in the rising and falling of the waves in the sea.
    • Wind velocity and fetch are two factors that influence wave energy.
  • 6. Wind velocity
    • Wind velocity determine wind energy which in turn determine wave energy.
    • The higher the wind velocity, the larger and more powerful the waves will be.
    • Lower the wind velocity, the smaller and less powerful the waves will be.
  • 7. Fetch
    • Fetch refers to the distance in the open sea over which the wind blows as it moves towards land.
    • The greater the fetch, the larger and more powerful the waves.
    • Countries such as Japan and Australia have coasts that face large open oceans and seas.
    • These coasts are often battered by powerful waves due to large fetches.
  • 8. Wave
    • Waves are disturbance on the water surface by which energy is transferred from one place to another.
  • 9. Wave
    • When waves reach the shallow water near the coast, the circular movements of the water particle change to elliptical (oval) movements.
    • The shallow sea bed obstructs the movement of the water (wave velocity and energy decreases).
  • 10. Wave (continue)
    • The rapid travelling waves behind the first wave will push against it, causing the first wave’s height to be increased while its length to be shorten.
    • The first wave then crashes onto the beach, its crest trapping air and causing foamy water to rush up the beach.
  • 11.  
  • 12. Swash
    • Swash is the movement of the waves up the shore towards land.
    • As the waves rush up the shore, they transport materials up the shore.
    • However, the waves soon lose their energy and retreat under the pull of gravity.
  • 13. Backwash
    • Backwash is the movement of the waves down the shore towards the sea.
    • As the waves move down the shore, they also transport materials down the sea.
  • 14. Constructive waves
    • Constructive waves are waves with strong swash and a weaker backwash.
    • They are also known as spilling breakers because they spill over when they break on the shore.
    • As they move up the beach they help to deposit sediments on the beach.
  • 15. Destructive waves
    • Destructive waves are waves with strong backwash and a weaker swash.
    • They are known as plunging breakers because they plunge when they break on the shore.
    • As they retreat towards the sea, they erode and carry away a large amount of sediments from the beach.
  • 16.  
  • 17. Different coastal processes
    • Erosion
    • Transportation
    • Deposition
  • 18. Erosion
    • Corrasion (abrasion)
      • Waves carry rock fragments such as cobbles, pebbles and gravel.
      • When these rock fragments are thrown against the coast, they are like chiselling tools, cutting up and breaking the rocks forming the coast.
  • 19. Erosion
    • Attrition
      • When rock fragments carried by the waves are thrown against one another, they gradually break up into smaller, smoother and more rounded pieces.
  • 20. Erosion
    • Solution (corrosion)
      • Soluble minerals in coastal are dissolved in and removed by the seawater.
      • E.g. calcium carbonate in limestone reacts chemically with the carbonic acid in the seawater and changes into soluble calcium hydrogen carbonate.
      • When solution occurs the rocks are weakened and will ultimately disintegrate.
  • 21. Erosion
    • Hydraulic action
      • The weight of the waves smashing against the coast repeatedly can weaken and loosen rocks so that ultimately they break off.
  • 22. Transportation
    • Agents
      • Wave & current
    • Longshore drift
  • 23.  
  • 24.  
  • 25. This movement of sediment along the coastline is called longshore drift . Direction of movement swash Backwash Backwash is always at right angles to the beach Longshore drift
  • 26. Longshore drift
    • Waves approach the coast at an angle, depending on the wind direction.
    • When waves reach the coast at angle, the swash carries sediments up onto the coast at that angle.
    • The backwash then carries the sediments back to the sea at a right angle to the coast due to the influence of gravity.
  • 27. Longshore drift
    • This motion is repeated and gives rise to a zig-zag movement of sediments along the coast.
    • This zig-zag movement is one way in which sediments are moved along the coast.
    • The movement of sediment is sometimes helped by longshore currents.
    • This result in longshore drift which is the movement of sediments parallel to the coast.
  • 28. Deposition
    • Deposition of sediments takes place along the coast when the waves lose their energy.
    • The deposited sediments will remain in the same spot until the next wave picks it up and transport it further along the beach.
    • In many instances the deposited sediments start to form depositional features along the coast.
    • However, these features can be easily destroyed by large storms such as hurricanes.
  • 29. Deposition (continue)
    • One effect of the longshore drift is the sorting and depositing of sediment on the shore.
    • In the course of moving the sediments up and down the shore by swash and backwash, the sediments are sorted and deposited according to size.
    • Coarser and larger sediments are usually deposited further up the shore as they are transported and deposited at the highest point on the beach y strong swashes.
    • The finer and smaller sediments are usually deposited nearer the shoreline.
    • However, their size enable them to be easily transported up on the beach by swash and to be just easily eroded by backwash.
  • 30. Homework
    • Sec 3 NA
    • Workbook pg 21 to 22