1. WAVES

2. Wave – propagation of energy through a medium. Speed is determined by the properties of the medium. Gravity waves – sufficiently large waves where gravity acts as the restoring force (force that causes the water to return to its undisturbed level) Ripple (or Capillary) waves – surface tension acts as the restoring force

3. Wind is the most common generating force Capillary waves are formed and grow to form gravity waves.

4. Fetch – continuous area of water over which the wind blows in essentially the same direction.

5. Anatomy of a Wave

6. Measures of a Wave Period – the time required for two successive crests or troughs to pass a point. (depends on the generating force) Wave Speed: speed = length of wave C= L/T wave period C = celerity (wave speed) L = wavelength T = Period

7. Dispersion – faster waves move through slower waves (Sorting) Long period, Long wavelength = Greater Speed Short period, short wavelength =Lesser Speed Wave trains = faster waves; packets of similar waves with the same period & speed Swell = faster, longer period waves; uniform, free waves

8. Wave Interaction When waves meet, they pass through each other and move on. Constructive Interference – waves meet crest to crest, reinforcing one another (LARGE AMPLITUDE) Destructive Interference – waves meet crest to trough, cancelling one another (SMALLER AMPLITUDE)

10. Wave Height- The height of a wave is controlled by the interaction of several factors: 1.Wind speed 2.Wind duration 3.Fetch 40-50° latitude – roaring forties/furious fifties Ideal for the production of high waves… No landmasses to interfere High intensity storms Strong winds of long duration (westerlies)

11. Episodic (Rogue) Waves Large waves that suddenly appear, unrelated to local sea conditions Abnormally high wave that occurs because of a combination of intersecting wave trains, changing depths and currents Occur most frequently near the edge of continental shelves (200m deep) and in certain areas with prevailing wind, wave & current patterns Heights: 7 to 8 stories high (1/2 mile λ)

12. Episodic (Rogue) Waves Algulhas current area ~ 57.9 meters (190 feet) North Sea ~ 33.8 meters (111 feet) http://www.youtube.com/watch?v=urP3kT6dCtk http://www.youtube.com/watch?v=urP3kT6dCtk

13. More Rogue Waves… http://www.youtube.com/watch?v=WtGi42nxu8s Rogue wave http://www.youtube.com/watch?v=yLzgzvVxUV4 http://www.youtube.com/watch?v=yLzgzvVxUV4

14. Wave Steepness Steepness = HeightS = H Length L There is a maximum possible height for any given wavelength. If the ratio exceeds 1:7, the wave breaks Whitecaps – short wavelengths (1m), wind increases their height rapidly.

15. Shallow Water Waves As waves enter shallow water, they “feel” the bottom and friction reduces the forward speed of the wave Speed reduction = wavelength reduction = increased height The wavelength and speed are controlled by water depth.

16. Refraction As waves move from deep water to shallow, they bend or refract. Result: change wavelength and speed

17. Refraction

19. Reflection Waves bounce off of cliffs, steep beaches, breakwaters, bulkhead or other structures that are straight. Waves passes through incoming waves to produce an interference pattern.

21. Diffraction The spreading of wave energy sideways to the direction of wave travel. After they pass the barrier, crests decrease in height and energy is transported sideways.

22. DDiffraction http://www.youtube.com/watch?v=IZgYswtwlT8

23. The Surf Zone Shallow area along the coast in which the waves slow rapidly, steepen, break and disappear in turbulence If shallow water depths extend offshore for some distances, the surf zone is wider than over a sharply sloping shore. Longer, higher waves become unstable and break farther offshore Breakers – breaking waves

24. The Surf Zone Plungers – break with a sudden loss of energy and a splash. Form on narrow, steep beach slopes Spillers – less dramatic wave form consisting of turbulent water and bubbles flowing down the collapsing wave face. Form over wider, flatter beaches where energy is extracted more slowly over shallow bottom Spillers give surfers a longer ride, but plungers give a more exciting one

25. Tsunamis Tsunami ~ seismic sea wave; Japanese word meaning “harbor wave.” When the earth’s crust suddenly is moved up or down, it causes the sea surface to move as well. Long wavelength (100-200km; 60-120 miles) Tsunamis are shallow water waves because the depth of the ocean (4000m; 1300ft) is less than 1/20 th the wavelength Velocity = 200m/s (400mph)

27. Tsunamis When a tsunami first forms, height = 1-2 m but this height is over many kilometers. Energy is distributed from the surface to the floor over the length of the wave As it reaches the coast, it slows (50mph), its wavelength decreases, and energy is compressed into a smaller water volume. Result: wave height builds rapidly Loss of energy is rapid when wave breaks.

28. Tsunamis