THE WORK OF WAVES: Coastal Landforms

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Chapter Outline

  • 19.1

    Coastal Processes: Tides, Waves, and Longshore Currents

  • 19.2

    Coastal Landforms: Beaches and Rocky Coasts

  • 19.3

    Geographic Perspectives: The Sisyphus Stone of Beach Nourishment
These spherical boulders, called the Moeraki Boulders, lie on the beach near Hampden, South Island, New Zealand. The boulders are about 60 million years old and as large as 2 m (6.5 ft) across. They were embedded in sedimentary rocks on a coastal cliff until erosion freed them and they tumbled to the beach.
(Ben Pipe/Getty Images)

LIVING PHYSICAL GEOGRAPHY

  • What causes the tides?

  • What are rip currents and why are they deadly?

  • Why are some beaches black?

  • Why is the sand on many beaches artificial?

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THE BIG PICTURE

Coastal beaches and rocky shores are shaped by wave energy. Human activities have contributed to the loss of sand from beaches through erosion.

LEARNING GOALS

After reading this chapter, you will be able to:

  • 19.1

    Discuss the role of tides and wave energy in coastal landform development.

  • 19.2

    Describe landforms on beaches and rocky coasts and explain how they form.

  • 19.3

    Assess and evaluate the practice of restoring eroded beaches by artificial replenishment of sand.

THE HUMAN SPHERE:

Mavericks

FOR MOST OF THE YEAR, the world’s professional-class surfers are scattered around the globe, working to hone their surfing skills. Once a year, between January and March, 24 preselected surfers may get the phone call telling them that the Mavericks Invitational surf competition is about to begin. They will have 24 hours to travel to Half Moon Bay, in Northern California, where they will surf some of Earth’s largest and most powerful waves. The waves at Mavericks routinely reach heights of 10 m (33 ft), and waves as high as a six-story building, 24 m (80 ft), have been witnessed there (Figure 19.1). These high coastal waves are the result of swells, waves that are generated in the open ocean. As the swells approach the coast, they encounter a gradually sloping seafloor at Mavericks that channels their energy into a focused area.

Figure 19.1

Riding wave energy. A surfer rides a large wave at the Mavericks Invitational in Northern California in 2012.
(© Ezra Shaw/Getty Images)

The waves of the ocean possess a considerable amount of energy, and they never rest. This chapter explores the ways in which wave energy shapes the coast and the landforms that result from it. Because waves are generated by wind, and wind is generated by solar heating, the erosional energy of coastal waves is ultimately derived from the Sun.

We begin this chapter by exploring tides, waves, and coastal currents. We next examine sandy and rocky shores and the landforms associated with each. Finally, we examine the problem of maintaining sand at popular coastal beaches.

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