Waves
Apr 01, 2015
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.