Erosion

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Erosion

  1. 1. The Work of Waves and Wind• Objectives:• Explain the characteristics of ocean waves and tides• Present coastline features of erosion, transport and deposition• Examine the processes of wind erosion and deposition• Differentiate different types of dune• Describe the wind deposit LOESS
  2. 2. COASTAL LANDFORMS wave length crestwave troughheight particles in waves follow a circular pattern
  3. 3. At the shoreline• Water becomes shallow, wave height increases because wave length decreases• Waves become steeper, then collapse (breakers)
  4. 4. • Surf - sequence of breaking waves• Swash - water sliding up beach• Backwash - water flowing back down beach to sea
  5. 5. Wave refraction• Close to coast, water gets more shallow• Waves are slowed down• If waves arrive at an angle, one part is slower than the rest• Causes waves to bend = wave refraction
  6. 6. Wave refraction Bay Headland
  7. 7. • Waves arriving at bays are slow (deposition)• At headlands, faster (erosion)
  8. 8. • A sequence of features is produced as headlands are degraded• Sea cliffs• Waves erode base the cliff -undercutting retreats
  9. 9. • Also producessea caves• As cliffs retreatproduces a wave-cut platform
  10. 10. • Headlandsmay be erodedback leaving aremnant (stack) stack
  11. 11. Longshore drift• Waves arrive at a coast at an angle (swash)• Backwash returns at 90 degrees Sand is moved along the beach = longshore drift or longshore current
  12. 12. Coastal deposition• Result of longshore drift and a lot of sediment• = produces extensions of deposit from the shoreline
  13. 13. spit = curved extension• May grow across a bay (baymouth bar)• May link an island to the main land (tombolo)
  14. 14. TIDES Moon/• Daily changes in sea levels Sun• Tides rise (FLOOD) to producea HIGH TIDE• And fall (EBB) (LOW TIDE)• Produced by the gravitationalpull that the Sun and Moon exerton the Earth’s surface (includingthe oceans)
  15. 15. This side is pulled towards the Sun and/or Moon by gravitational attraction This side bulges out because of inertiaTherefore, there are two high tides on Earth at any one time
  16. 16. Every 24 hours 50 minutes any point on theEarth rotates through two bulgesEach location experiences 2 high (FLOOD)tides and 2 low (EBB) tides
  17. 17. Types of CoastlineSubmergence and emergence changescoastlines Pocket beaches
  18. 18. Emergent coast• Uplifted land surface• Coastal landforms are found above present sea level a wave-cut platform when elevated - uplifted marine terrace
  19. 19. Submergent coast• Rise in sea level• Submergent coast• Landforms under water• A ria coastline is an example of submergence
  20. 20. Submergence Shorlines• Ria coast - shorline valleys eroded by rivers are submerged – has many offshore islands – exposure to waves erodes islands and headlands• Fiord coast - shoreline valleys created by glaciers are submerged – valleys are deep and straight – because of the depth, there are few beaches
  21. 21. Barrier Island Coasts• Occur on low lying coasts with gentle gradients• BARRIER ISLANDS - low ridges of sand built by waves – behind the islands are lagoons – shallow water with tidal deposits• TIDAL INLETS - gaps between the islands
  22. 22. Delta and Volcano Coasts• DELTA - deposit by rivers entering the sea• Water slows down and spreads out as it enters• Channel divides and subdivides to create DISTRIBUTARIES• Volcano coasts develop in volcanic deposits• Low cliffs form in fresh lava
  23. 23. Coral reefs• Corals build up calcium deposits to produce reefs• To grow, corals need: – Clear, warm, shallow water – Wave action Corbis Digital Stock
  24. 24. Coral reefs• Fringing reef - directly attached to an island or coast• Barrier reef - lagoon between coast and reef• Atoll reef - circular reef surrounding a lagoon (no land in centre)
  25. 25. AEOLIAN (Eolian) LANDSCAPES Wind erosion, transport and depositionOccurs in dry regions, with little vegetation such as deserts and coastal landscapes
  26. 26. Wind Erosion• Faster the air flows, more erosion• Erodes more rapidly if wind blows constantly from one direction• 2 TYPES OF WIND EROSION – ABRASION and DEFLATION
  27. 27. DEFLATION HOLLOWSRemoval of fine particles by wind leaveshollows behind (DEFLATIONHOLLOWS)Also leaves a surface of closely packedstones (DESERT PAVEMENT)
  28. 28. WIND TRANSPORTATION- Very fine material may be carried insuspension in the air- But larger particles may be moved by 2methods: SURFACE CREEP & SALTATION
  29. 29. 1.) SURFACE CREEP- material is rolled along the surface- accounts for 20% of wind transport
  30. 30. 2.) SALTATION- The asymmetrical bouncing of sandgrains- Accounts for 80% of wind transport- Cause of shifting sand dunes
  31. 31. Aggradational land formsSAND SEAS (ERGS)= only 25% of the worlds desertssurface may be covered in RIPPLES
  32. 32. SAND DUNESare ridges of winddeposited sand- Usually 3 to 15metres high, but canreach 180 metres- A continuouslychanging dune isACTIVE Corbis Digital Stock
  33. 33. The formation ofdunes depends on: - amount of sand - speed and direction of wind - occurrence of vegetation Corbis Digital Stock
  34. 34. wind directionBACKSLOPE SLIPFACE crest angle of of sand repose ent m ov em
  35. 35. TYPES OF SAND DUNE1.) BARCHAN- most common type- crescent-shaped backslope slip face Wind direction
  36. 36. 2.) PARABOLIC DUNES- crescent-shaped but with the concave sideon the windward side- usually elongated- may develop in associated with deflationhollows Wind direction
  37. 37. 3.) TRANSVERSE DUNES• low sand ridge at right angles to the winddirection• may form because of large amounts of sandwind
  38. 38. 4.) LONGITUDINAL DUNES• low sand ridges parallel to the wind direction• may form because of a limited amount of sand• also known as seif dunes wind
  39. 39. LOESS• Finely textured sediment wind-blown long distances• Wind-blown glacial debris formed large deposits
  40. 40. This powerpoint was kindly donated towww.worldofteaching.comhttp://www.worldofteaching.com is home to over athousand powerpoints submitted by teachers. This is acompletely free site and requires no registration. Pleasevisit and I hope it will help in your teaching.

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