Sec 3 - Lesson 1 Coasts


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Sec 3 - Lesson 1 Coasts

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