Waves and Shorelines

I. Waves

II. Effect of the shoreline

III. Wave Refraction

IV. Longshore Currents

V. Wave Erosion

VI. Wave Deposition

VII. Development of irregular coastlines

VIII. Implications for man

IX. Possible Essay Questions

X. Practice Questions


I. Waves

Source for Diagram: http://www.geology.uiowa.edu/~12_003/eh&r98/webversion/shorelines/sld006.htm

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II. Effect of approaching shoreline on waves

Source for Diagram: http://www.geology.uiowa.edu/~12_003/eh&r98/webversion/shorelines/sld008.htm

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III. Wave refraction around headlands

Source for Diagram: http://www.geology.uiowa.edu/~12_003/eh&r98/webversion/shorelines/sld013.htm

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IV. Longshore currents and beach drift

Source for Diagram: http://www.lifeguard-csla.org/surfbear/rips.htm

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V. Wave erosion

SEE SEA STACK AND SEA ARCH DEVELOPMENT

SEE HISTORY OF A SEA STACK

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VI. Wave deposition

  • When the velocity of the wave currents or the longshore currents decreases, the transported material will be deposited.

  • Wave deposition is most active in bays where the wave energy is dissipated.

  • Features produced by wave or longshore current deposition -

    • Beach - A sand deposit along the shoreline.

    • Baymouth bar - A linear sand deposit that is continuous across the mouth of a bay.

    • Spit - A linear sand deposit that is connected only at one end to the shore.

      Source for Diagram: http://www.geology.uiowa.edu/~12_003/eh&r98/webversion/shorelines/sld017.htm

    • Tombolo - A sand deposit that connects a stack or island to the shore.

    • Barrier island - A sand deposit that is offshore and parallel to the shore.

Source for Diagram: http://www.cnmoc.navy.mil/educate/neptune/quest/ports/beaches.htm

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VII. Development of irregular coastlines

  • Wave energy is concentrated on headlands due to wave refraction; erosion is maximum.

  • Longshore currents and beach drift diverge from the headlands due to wave refraction.

  • Wave energy is dispersed in the bays; deposition is maximum.

  • Headland cliffs are cut back by wave erosion and the bays are filled with sand deposits until the coastline becomes straight.

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VIII. Implications for man

  • Beaches will erode away when their sand supply is cut off by a dam on a river and sand no longer enters the beach drift.

  • Construction of a breakwater protects the beach from erosion and allows sand to deposit in the protected harbor.

  • Construction of jetties will allow sand to deposit on the updrift side and cause beach erosion on the downdrift side.

  • Trying to stop wave erosion of sea cliffs and shoreline features is economically unfeasible.

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IX. Possible essay questions

  • Define and illustrate the following terms: wave crest, wave trough, wave height, wavelength, and wave base.

  • Describe and illustrate what happens to a wave as it approaches a shoreline.

  • Illustrate and explain why it is that waves refract (bend) around headlands.

  • Describe and illustrate the origin of longshore currents and beach drift.

  • Describe and illustrate the origin of a wavecut cliff.

  • Describe and illustrate the origin of a wavecut platform.

  • Describe and illustrate the origin of a baymouth bar.

  • Describe and illustrate the origin of a spit.

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X. Practice Questions

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