# WAVES Chapter 10 What causes waves Most waves

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WAVES Chapter 10

What causes waves? ©Most waves are caused by wind © Tides © Earthquakes STORMS (energy in) SWELL (waves move away from the sea that generated them; this energy can travel across an entire ocean basin like the Pacific Ocean) SURF (energy out)

How tall is a wave? ©Height is measured from crest to trough.

~~~Wavelengths~~~ ©Wavelengths are measured from the crest of one wave to the crest of the next wave.

Period ©Period is the amount of time across a wavelength. ©The time from wave to wave. ©To do this, measure the time from when the first crest hits until the next crest hits to same point.

Wave Velocity ©Velocity is the speed of the wave (velocity = distance) time ©To do this, measure the wavelength, then divide by the period.

Factors Affecting Wind Wave Development What factors affect wind wave development? Wind strength - wind must be moving faster than the wave crests for energy transfer to continue Wind duration - winds that blow for a short time will not generate large waves Fetch - the uninterrupted distance over which the wind blows without changing direction © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Why do waves break? ©Water particles move in circular patterns. When the depth of the water is less than 1/2 the wavelength, the wave hits bottom. The length rolls over to become the height and the wave breaks.

Wind Waves Approaching Shore What different ways can waves break against the shore? Plunging waves break violently against the shore, leaving an air-filled tube, or channel, between the crest and foot of the wave. Plunging waves are formed when waves approach a shore over a steeply sloped bottom. Spilling waves occur on gradually sloping ocean bottoms. The crest of a spilling wave slides down the face of the wave as it breaks on shore. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

CURL ©Curl is the circular pattern of waves caused by wind blowing over the crest of a wave.

Ocean Waves Note that the water molecules in the crest of the wave move in the same direction as the wave, but molecules in the trough move in the opposite direction. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

The water particle moves in a vertical circle as the wave passes. The particle moves forward with the wave crest, and backward with the wave trough © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Types of waves © Seiche waves are without a crest or trough. They cause the rocking motion in bays and marinas. © Rogue waves are caused by the collision of two water masses with different densities. They appear suddenly and may capsize boats. © Tsunamis are the result of earthquakes on the ocean floor. They are very long, low invisible waves in the open ocean. © Tidal waves are a combination of storms and high spring tides. They are very different from a tsunami.

Classifying Waves © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Rogue waves This illustration shows an oil tanker encountering a rogue wave. A deep trough, or “hole in the ocean” as it is called, drops 15 m below the still water line. The bow of the vessel is than over taken by the large crest, that might be 15 m above the still water line. The huge amount of water causes major damage to the ship and might even cause it to sink.

Tsunamis © By the time they reach the shore and break, the wave height may be 100 ft. high and may travel at 400 miles/hour.

Harnessing Wave Energy ©Water entering the top of the wave generator causes the turbine to spin which will produce electricity. ©Tidal Bores - Energy Harvest? Lockeed Corp’s Dam. Atoll