Erosion

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  • 1. Erosion Junhel C. Dalanon, DMD, MAT SNSCLC – Minglanilla Minglanilla, Cebu, Philippines 6046
  • 2. 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
  • 3. wave length wave height crest trough particles in waves follow a circular pattern COASTAL LANDFORMS
  • 4. At the shoreline
    • Water becomes shallow, wave height increases because wave length decreases
    • Waves become steeper, then collapse (breakers)
  • 5.
    • Surf - sequence of breaking waves
    • Swash - water sliding up beach
    • Backwash - water flowing back down beach to sea
  • 6. 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
  • 7. Wave refraction Bay Headland
  • 8.
    • Waves arriving at bays are slow (deposition)
    • At headlands, faster (erosion)
  • 9.
    • A sequence of features is produced as headlands are degraded
    • Sea cliffs
    • Waves erode base - undercutting
    the cliff retreats
  • 10.
    • Also produces sea caves
    • As cliffs retreat produces a wave-cut platform
  • 11.
    • Headlands may be eroded back leaving a remnant ( stack )
    stack
  • 12. 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
  • 13. Coastal deposition
    • Result of longshore drift and a lot of sediment
    • = produces extensions of deposit from the shoreline
  • 14.
    • May grow across a bay (baymouth bar)
    • May link an island to the main land (tombolo)
    spit = curved extension
  • 15.
    • TIDES
    • Daily changes in sea levels
    • Tides rise (FLOOD) to produce a HIGH TIDE
    • And fall (EBB) (LOW TIDE)
    • Produced by the gravitational pull that the Sun and Moon exert on the Earth’s surface (including the oceans)
    Moon/ Sun
  • 16. This side is pulled towards the Sun and/or Moon by gravitational attraction This side bulges out because of inertia Therefore, there are two high tides on Earth at any one time
  • 17. Every 24 hours 50 minutes any point on the Earth rotates through two bulges Each location experiences 2 high (FLOOD) tides and 2 low (EBB) tides
  • 18. Types of Coastline Submergence and emergence changes coastlines Pocket beaches
  • 19. Emergent coast
    • Uplifted land surface
    • Coastal landforms are found above present sea level
    a wave-cut platform when elevated - uplifted marine terrace
  • 20. Submergent coast
    • Rise in sea level
    • Submergent coast
    • Landforms under water
    • A ria coastline is an example of submergence
  • 21. 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
  • 22. 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
  • 23. 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
  • 24. Coral reefs
    • Corals build up calcium deposits to produce reefs
    • To grow, corals need:
      • Clear, warm, shallow water
      • Wave action
    Corbis Digital Stock
  • 25. 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)
  • 26. AEOLIAN (Eolian) LANDSCAPES Wind erosion, transport and deposition Occurs in dry regions, with little vegetation such as deserts and coastal landscapes
  • 27. 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
  • 28. DEFLATION HOLLOWS Removal of fine particles by wind leaves hollows behind (DEFLATION HOLLOWS) Also leaves a surface of closely packed stones (DESERT PAVEMENT)
  • 29. WIND TRANSPORTATION - Very fine material may be carried in suspension in the air - But larger particles may be moved by 2 methods: SURFACE CREEP & SALTATION
  • 30. 1.) SURFACE CREEP - material is rolled along the surface - accounts for 20% of wind transport
  • 31. 2.) SALTATION - The asymmetrical bouncing of sand grains - Accounts for 80% of wind transport - Cause of shifting sand dunes
  • 32. Aggradational land forms SAND SEAS (ERGS) = only 25% of the world's deserts surface may be covered in RIPPLES
  • 33. SAND DUNES are ridges of wind deposited sand - Usually 3 to 15 metres high, but can reach 180 metres - A continuously changing dune is ACTIVE Corbis Digital Stock
  • 34. The formation of dunes depends on: - amount of sand - speed and direction of wind - occurrence of vegetation Corbis Digital Stock
  • 35. wind direction BACKSLOPE SLIPFACE movement of sand angle of repose crest
  • 36. TYPES OF SAND DUNE 1.) BARCHAN - most common type - crescent-shaped Wind direction backslope slip face
  • 37. 2.) PARABOLIC DUNES - crescent-shaped but with the concave side on the windward side - usually elongated - may develop in associated with deflation hollows Wind direction
  • 38.
    • 3.) TRANSVERSE DUNES
    • low sand ridge at right angles to the wind direction
    • may form because of large amounts of sand
    wind
  • 39.
    • 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
  • 40. LOESS
    • Finely textured sediment wind-blown long distances
    • Wind-blown glacial debris formed large deposits