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    Erosion Erosion Presentation Transcript

    • Erosion Junhel C. Dalanon, DMD, MAT SNSCLC – Minglanilla Minglanilla, Cebu, Philippines 6046
    • 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
    • wave length wave height crest trough particles in waves follow a circular pattern COASTAL LANDFORMS
    • At the shoreline
      • Water becomes shallow, wave height increases because wave length decreases
      • Waves become steeper, then collapse (breakers)
      • Surf - sequence of breaking waves
      • Swash - water sliding up beach
      • Backwash - water flowing back down beach to sea
    • 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
    • Wave refraction Bay Headland
      • Waves arriving at bays are slow (deposition)
      • At headlands, faster (erosion)
      • A sequence of features is produced as headlands are degraded
      • Sea cliffs
      • Waves erode base - undercutting
      the cliff retreats
      • Also produces sea caves
      • As cliffs retreat produces a wave-cut platform
      • Headlands may be eroded back leaving a remnant ( stack )
    • 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
    • Coastal deposition
      • Result of longshore drift and a lot of sediment
      • = produces extensions of deposit from the shoreline
      • May grow across a bay (baymouth bar)
      • May link an island to the main land (tombolo)
      spit = curved extension
      • 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
    • 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
    • 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
    • Types of Coastline Submergence and emergence changes coastlines Pocket beaches
    • Emergent coast
      • Uplifted land surface
      • Coastal landforms are found above present sea level
      a wave-cut platform when elevated - uplifted marine terrace
    • Submergent coast
      • Rise in sea level
      • Submergent coast
      • Landforms under water
      • A ria coastline is an example of submergence
    • 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
    • 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
    • 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
    • Coral reefs
      • Corals build up calcium deposits to produce reefs
      • To grow, corals need:
        • Clear, warm, shallow water
        • Wave action
      Corbis Digital Stock
    • 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)
    • AEOLIAN (Eolian) LANDSCAPES Wind erosion, transport and deposition Occurs in dry regions, with little vegetation such as deserts and coastal landscapes
    • Wind Erosion
      • Faster the air flows, more erosion
      • Erodes more rapidly if wind blows constantly from one direction
    • DEFLATION HOLLOWS Removal of fine particles by wind leaves hollows behind (DEFLATION HOLLOWS) Also leaves a surface of closely packed stones (DESERT PAVEMENT)
    • 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
    • 1.) SURFACE CREEP - material is rolled along the surface - accounts for 20% of wind transport
    • 2.) SALTATION - The asymmetrical bouncing of sand grains - Accounts for 80% of wind transport - Cause of shifting sand dunes
    • Aggradational land forms SAND SEAS (ERGS) = only 25% of the world's deserts surface may be covered in RIPPLES
    • 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
    • The formation of dunes depends on: - amount of sand - speed and direction of wind - occurrence of vegetation Corbis Digital Stock
    • wind direction BACKSLOPE SLIPFACE movement of sand angle of repose crest
    • TYPES OF SAND DUNE 1.) BARCHAN - most common type - crescent-shaped Wind direction backslope slip face
    • 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
      • low sand ridge at right angles to the wind direction
      • may form because of large amounts of sand
      • low sand ridges parallel to the wind direction
      • may form because of a limited amount of sand
      • also known as seif dunes
    • LOESS
      • Finely textured sediment wind-blown long distances
      • Wind-blown glacial debris formed large deposits