Chapter 11
Oceans and Coasts

Coastal Zone:

  • Broad zone where continents meet oceans
  •  Different oceanic processes occur in this zone, mainly waves and tides.
  •  At any particular time, coastal processes occur in restricted narrow zone relative to other geologic processes -> rivers, wind, etc.

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    However, coastal zones appear to migrate landward or seaward due to changes in sea level, uplift or subsidence, etc.

    Although coastal zones change constantly, 2/3 of world’s population is found in coastal cities - because of their strong appeal

  • Many world’s largest cities are found here e.g., New York, Los Angeles, New Orleans, Tokyo, London, Rio de Lenerio, Shanghai, Sidney, Cicily, Lagos, etc.

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    Types of Coasts

  •  2 main types

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    A.Cliff Coasts:

    B. Barrier Coasts: Ocean -> barrier island -> lagoon -> main land Figure here.

    Coastal Zone Processes Tides: ONCE or TWICE daily, ocean water level falls and rises


    ---Rise found to be few cm to 15 cm.

     Waves: Oscillations of water surface Occur on all bodies of H2O but are very significant in oceans.

  •  Are agents of erosion, transportation & deposition

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    Figure here.

  • The wind transfers some energy to the water to produce waves.
  •  Causing the water surface to oscillate.
  •  As more wind blows, more waves are formed.
  •  Waves differ in size, e.g., during storms, waves are bigger

    • Figure here.
  • Big waves have greater velocities
  •  Big waves can outrun small waves.

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    Wave Xteristics

  •  As a wave enters shallow water, it becomes oversteepened
  •  The wave crest advances faster than wave form.
  •  Crest then plunges forward as a BREAKER.

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    Figure here.

    Currents: (2 types)

    1.  Longshore currents:
  • Rip Currents:
    • Deposition in Coastal Zones
  •  Deposits include BEACHES, SPITS, BAYMOUTH, BARS and BARRIER BARS.

    • Beaches:
  •  Unconsolidated sediments extending landward from sea. - Different parts.

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     Seasonal Changes in Beaches

    Summer Beaches are

    1.  covered with sand generally
    2.  have wide berms (a gentle sloping beach face)
    3.  a smooth offshore profile
    Winter Beaches are
    1.  coarser grained & steeper
    2.  have small berms or none
    3.  have sand bars parallel to shoreline.
    Figure here.
  • Change in shape is related wave intensity
  •  In winter, storm waves have more energy. Therefore, sand is eroded & transported from beach offshore & retained as a sand bar.

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    - In summer, waves are gentler.

  •  The same sand that was carried offshore during winter is returned onshore.
  •  Volume sand remains almost constant

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    Spits & Baymouth Bars

    Figure here.

    Coastline Erosion

    Corrosioin: the wearing away of rock by chemical processes
    Hydraulic action: erosion due to the forces of water.
    Abrasion: erosion from the grinding of rock & sand carried by waves
    The rate of retreat of seacliff may be high
    e.g., at Cape Cod, Massachusetts, retreat was observed to be as much as 30 m per century.

    Protection of Coastline

    1.  Construction of JETTIES
      2. Figure here.
    2. Sea Wall (Concrete)
    3. Rock revetments (????)
    4.  - Reinforcements with large blocks of rocks.

      5.  

       
       
       

      Figure here.

    5. Break Water
      6. Figure here.
    6. Groins
    Figure here.
     

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