Chapter 12: Effects of Wind, Waves and Currents Section II: Waves in the Sea

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# Chapter 12: Effects of Wind, Waves and Currents Section II: Waves in the Sea - PowerPoint PPT Presentation

Chapter 12: Effects of Wind, Waves and Currents Section II: Waves in the Sea. On average the wavelength is 20-30 times its height . Features of Water Waves. The period of a wave is the time it takes one wavelength to pass a given point.

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The period of a wave is the time it takes one wavelength to pass a given point.

• Most ocean waves have a period that ranges from 2s to 10s.
• Speed=wavelength/period
• Find the speed of a wave 30m long with a period of 5 sec.
• 6 m/s
Refraction:
• Waves approach shoreline at an angle, when they reach shallow water they swing around and approach relatively head on = refraction

Water is not carried along with the motion of a wave.

• Each water particle moves in place in a circular motion.
• Water particles bump into the next one and passes the energy along, passing the energy through the water.
• Wave motion also takes place below the surface, moving water molecules in smaller and smaller circles.
Origin of Breakers

Video

• Waves approach the shoreline smoothly until they reach water so shallow that they touch the bottom.
• Water depth is usually about half the wavelength
• The lower part of the wave slows down
• The upper part of the wave moves ahead, until there is not enough water to support the wave
• The crest falls over and breaks into surf.
• The line of breakers is where the crests break
• Surf is a powerful agent of erosion.
Shoreline Currents
• Waves may come from any direction, most strike the shore at an angle.
• The motion of water up the beach is swash, it moves sand up the beach at an angle.
• Most water runs back down the beach in a backwash current, which drags sand straight back to the sea.
• A very strong backwash is an undertow.
Shoreline Currents

A longshore current forms beyond the breakers and runs almost parallel to shore.

Rip currents are strong surface currents that flows away from the beach.