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

1. Chapter 12: Effects of Wind, Waves and CurrentsSection II: Waves in the Sea

2. On average the wavelength is 20-30 times its height. Features of Water Waves

3. 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

4. Refraction: • Waves approach shoreline at an angle, when they reach shallow water they swing around and approach relatively head on = refraction

5. Direction of Wave Advance: Video Animation

6. 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.

7. 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.

8. 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.

9. 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.