Waves

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Ocean Waves Move Energy across the Sea Surface

Ocean waves are visual proof of the transmission of energy across the surface of the ocean.

A floating sea gull demonstrates that wave forms travel but the water itself does not.

Fig. 10-1, p. 266

Wave directionWave

Stepped Art

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1604/es1604page01.cfm?chapter_no=visualization

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Wavelength Is the Most Useful Measure of Wave Size

Waves transmit energy across the ocean’s surface.

Wave energy in the ocean is a function of the wave period.

Most wave energy is typically concentrated in wind waves.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Progressive waves.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Wave Speed (m/sec)

equal to wavelength divided by period.

Example: What is the speed of a wave whose wavelength is 40 m and the period is 20 sec?

speed = 40 m/20 sec = 2 m/sec

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Wind Blowing over the Ocean Generates Waves

Wind waves are gravity waves formed by the transfer of wind energy into water waves.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Larger Swells Move Faster

Swell: The smooth curve of water caused by a wave

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Wave Development

• Wind strength – Faster wind= stronger waves

• Wind duration – Winds blowing longer=bigger waves

• Fetch - the uninterrupted distance over which the wind blows without changing direction. More fetch= stronger waves

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

When does a wave break?

• (1) The swell “feels” bottom when the water is shallower than half the wavelength.

• (2) The wave crests become peaked because the wave’s energy is packed into less water depth.

• (3) Circular wave motion is halted by hitting the ocean floor and slows the wave, while waves behind it maintain their original rate.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

• (4) The wave approaches the critical 1:7 ratio of a wave height to wavelength.

• (5) The wave breaks when the ratio of wave height to water depth is about 3:4.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

http://ca.pbslearningmedia.org/content/kqed07.sci.ess.bigwave/

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Tsunami

Tsunami are long-wavelength, shallow-water, progressive waves caused by the rapid displacement of ocean water.

Tsunami generated by the vertical movement of earth along faults are seismic waves.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

What else can generate tsunami?

• Landslides• Icebergs falling from glaciers

• Volcanic eruptions• Asteroid impacts• Other direct displacements of the water surface

© 2006 Brooks/Cole, a division of Thomson Learning, Inc.

Tsunami Have a Long and Destructive History

Eleven destructive tsunami have claimed more than 180,000 lives since 1990.