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# Waves and Water Dynamics

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### Waves and Water Dynamics

1. 1. Chapter 9: Waves and WaterDynamicsFig. 9-10
2. 2. Waves are moving energy Forces cause waves to move along air/wateror within water Wind (most surface ocean waves) Movement of fluids with different densitiesInternal waves often larger than surfacewaves Mass movement into oceanSplash waves
3. 3.  Seafloor movement Tsunami or seismic sea wave Gravitational attraction Earth, Moon,Sun Tides Human activities Wakes of ships Explosions
4. 4. Progressive waves Longitudinal “Push-pull” Transverse Side-to-side or up-and-down Orbital Circular orbit Ocean surface waves
5. 5. Types of wavesFig. 9-3a
6. 6. Wave characteristics Crest, trough Wave height is proportional to energy Wave length Wave height/wave length = wavesteepness Waves break when H/L is 1/7 Wave period, frequency
7. 7. Wave characteristics Wave base is 1/2 wave length Negligible water movement due to wavesbelow this depth Fig.9-6a
8. 8. Deep-water wave Depth of water is greater than1/2 wavelength Speed of wave form (celerity) isproportional to wavelength
9. 9. Shallow-water wave Water depth is less than 1/20 wavelength Friction with seafloor retards speed Wave speed (celerity) is proportional to depthof water Orbital motion is flattened
10. 10. Transitional waves Water depth is 1/2 to 1/20 ofwavelength Characteristics of deep andshallow-water waves Wave speed (celerity) isproportional to both wavelengthand depth of water
11. 11. Three types of waves
12. 12. Wave equations Wave speed = wavelength/period S = L/T Frequency = 1/period F = 1/T Wave speed (m/s) = 1.56 x period S = 1.56 x T
13. 13. Surface ocean waves Most wind-driven Small wind-driven waves Capillary waves Larger wind-driven waves Gravity waves
14. 14. Sea Storm at sea creates waves Wave energy depends on Wind speed Fetch Duration Chaotic mixture of differentwavelengths and wave heights
15. 15. Wave dispersion Longer wavelength wavesoutdistance shorter wavelengthwaves Waves travel in groups or trainswith similar characteristics Swell made up of waves ofsimilar wavelength and period
16. 16. Wave interference Constructive Wave heights increase Destructive Wave heights decrease Mixed Wave heights vary in wave train(surf beat)
17. 17. Interference illustratedFig. 9-14
18. 18. Rogue waves Unusually large waves Constructive interference Waves meet strong ocean currentFig. 9-16
19. 19. Rare photo of Rogue wave off Durban, SouthAfrica in 1980. The tower at the front right is 25 mabove sea level during flat seas!
20. 20. Click on Picture
21. 21. Shoaling waves Waves reach surf zone Wave speed decreases Wave length decreases Wave height increasesWave steepness 1/7, wave breaksSurface tension no longer able to holdwave together
22. 22. Wave speed and length decreasesand wave height increases. WhenWave steepness reaches 1/7 thewave will break.
23. 23. Breakers Spilling Gentle beach slope Plunging Moderately steep slope Surging Abrupt slope
24. 24. Spilling Breakers occur on beaches with gentle slopes. These waves break far from the shore, and thesurf gently rolls over the front of the wave.
25. 25. Plunging Breakers happen on beaches where the slope is moderately steep. This kind of wave normally curls over forming a tunnel untilthe wave breaks. Expert surfers love this type of wave!
26. 26. Surging Breakers happen on beaches where the slope is very steep. The wave does not actually break. Instead, it rolls onto thesteep beach. These kinds of breakers are known for their destructivenature.
27. 27. Wave refraction Shoaling waves bend so wave frontsapproach a shore nearly parallelFig. 9-19a
28. 28.  Wave energyfocused onheadland Wave energydispersed overbayFig. 9-19b
29. 29. Wave diffraction Wave energytransferredaround orbehind barriersFig. 9-20
30. 30. Wave reflection Waves bounce back from steepslopes or seawalls Reflected wave mayconstructively interfere withother waves
31. 31. Standing waves Two waves with same wavelengthmoving in opposite directions Node – no vertical movement Greatest horizontal movement Antinode – greatest vertical movement
32. 32. Fig. 9-22Click on Picture to SeeSurfers Riding StandingWaves
33. 33. Tsunami or seismic sea wave Caused by sudden changes involume of ocean basin Mainly submarine faults Volcanic eruptions Submarine landslides
34. 34. Fig. 9-23a
35. 35. Tsunami Very long wavelength Travels fast Raises sea level as crest shoals Trough causes sea level to fall Disastrous for infrastructure atcoasts Possibly much loss of life
36. 36. Tsunami warning system Monitor seismic activity Monitor changes in unusualwave activity Warning People evacuate
37. 37. End of Chapter 9: Waves andWater DynamicsFig. 9D