Chapter 8: Waves & Wave Dynamics

1. Chapter 8: Waves & Wave Dynamics

2. Where is the world’s premier big wave surf spot? Mavericks What are three things that make this site so challenging to surf?  Located off a point of land  Land extends into the ocean known for large waves and storms.  Deep water close to shore, narrow continental shelf. Who is famous for wiping out at the Mavericks …and surviving? Jay Moriarty

5. Slideshow of bathymetry of Half Moon Bay

7. 8.1: What Causes Waves? Define “wave”:  Moving energy traveling along the interface between ocean and atmosphere. (pg 244)  Waves are energy in motion (pg 247)  A disturbance that moves over the surface or through a medium with a speed determined by the properties of the medium. (pg 517)

8. All waves begin as a disturbance. List several examples of a disturbing force. A rock thrown into water.  Wind blowing  fluids of different densities  Landslides, underwater earthquakes

9. What are the 3 types of interface waves? a. ocean waves (air-water interface) b. atmospheric waves (air-air interface_ c. Internal waves (water-water interface)

11. What causes air-water interface waves? The movement of air/wind across the ocean What cause water-water interface waves? Difference in density Water-water interface waves are called Internal waves 10. How large can internal waves get? Over 100 m

12. 11. Internal waves can be created by a. Tidal movement b.Turbidity currents c. Wind stress d. Passing ships

13. 12. Describe what causes each type of wave: a. splash wave: landslides, calving icebergs Calving glacier (click HERE) b. tsunami: Underwater earthquakes Japan Tsunami 2011 (click HERE) Japan Tsunami raw footage (click HERE) c. tides: Gravitational pull of Earth & Moon d. wake: Human activity (boating, ships)

14. 8.2 How do Waves Move? What is a progressive wave? Waves that oscillate uniformly and travel without breaking. For each type of progressive wave, describe the movement. a. longitudinal wave: “push-pull” Motion in direction energy travels. b. transverse wave: “side to side” Motion is at right angle to direction of travel c. orbital (interface) waves: Combination of longitudinal & transverse Wave animation

15. 8.2 How do Waves Move? 15. What is meant by waveform? Shape of wave Wave animation

16. 8.3 What Characteristics do Waves Possess? 16. Still water level = E Wave animation

18. How is wave steepness calculated? S = Wave Height (H) Wavelength (L) If S ≥ 1/7 (0.14) the wave will break.

19. 19. Wave Period Time it takes for one wave (measured crest to crest) to pass a given point. Wave Frequency # of waves that pass a certain point in a given amount of time Relationship between Wave Period and Frequency As the period increases, frequency will decrease The longer it takes for each crest to pass a point means that the number of waves passing that point will decrease. They are INVERSELY proportional. Wave Simulator Wave Frequency Simulator

20. Deep-water Waves vs. Shallow-water Waves • Waves are classified as “deep” or “shallow” based • on the wave base. • Wave base is the depth at which no wave motion • is detected or is negligible. • Wave base = ½ of the wavelength (L/2) • (measured from still water line) • Wave Base animation NOAA Wave video

22. Deep-Water Waves • Depth (d)is greater than the wave base. • d > ½ L • Deep waves have no interference with the ocean bottom • They don’t “feel bottom”. • Particle movement is circular. • The circular orbits decrease in diameter with depth.

24. Shallow-Water Waves • Also known as “long waves” • Depth is less than 1/20 of the wavelength. • d < 1/20 L • They touch bottom or “feel bottom” • Speed affected by gravitational acceleration (g) and • water depth (d). • Particle movement is elliptical.

26. Transitional Waves • Wavelengths are between 2 and 20 times the depth. • They have characteristics of both deep and shallow waves.

28. Wave Speed • The speed (S) of a wave is referred to as celerity (C) • Speed (S) = wavelength (L) • period (T) • For deep-water waves, speed is proportional to wavelength. • S = 1.25 √ L • For shallow-water waves, speed is proportional to depth • S = 3.13 √ d • For transitional waves, speed depends on both wavelength • and depth.

30. 8.4: How Do Wind-Generated Waves Develop? • 1. Wind-driven waves begin as ripples called capillary waves and have a wavelength less than 1.74 cm. • 2. Define “restoring force”: Any force that destroys waves and restores the sea to a flat ocean

31. 3. As wind increases, the wave height and wavelength will increases, which will cause the waves “catch” more wind. • 4. Eventually, larger, symmetrical waves develop called gravitywaves.

32. 5. As the wave height increases, gravityreplaces capillarity as the restoring force. • 6. As more energy is transferred from the wind to the water (increases), what happens to the wave height, wavelength and wave form? Wave height increases faster than wavelength and the waveform becomes trochoidal.

34. 7. At what point does the properties of a wave no longer change? Wave speed = Wind speed • 8. List and DEFINE the 3 factors that determine the amount of energy in waves. a. Wind Speed: How fast the wind blows b. Duration:How long the wind blows c. Fetch: Distance the wind blows

35. 9. Wind speed is measured on a the BeaufortWindScale. • 10. What is the largest “authentic” wave recorded? 34 m (112 feet) wave observed by USS Rampano

36. 11. Describe the conditions that exist in a “fully developed sea”. Waves are at an equilibrium. Waves can no longer grow. Disturbing Force (wind energy) is equal to the restoring force (gravity.)

38. 12. Look at Table 8.2 on page 256. Compare each characteristic and describe the relationship between them. a. wind speed/ fetch: b. wind speed/ duration: c. wind speed/ wave height: d. wind speed/ wavelength: e. wavelength/ period: They are ALL directly proportional, as the first increases, so does the second.

40. 13. Define “swell”: Long-crested, uniform • symmetrical waves. • 14. As waves leave their area of origin (sea) and transition into a swell, they form groups of waves called wave trains. • 15. Which waves leave a “sea” area first? Waves with longer wavelengths, travel faster.

41. 16. Describe what happens to waves of a wave train as they disperse? Long fast waves change to short slow waves. • 17. The distance it takes for choppy seas to change to a uniform swell is called decay distance • 18. When two wave trains run together, they create interference.

42. Constructive Interference • Results in waves with the same wavelength, but the wave height doubles. • Waves with the same wavelength but come together crest to crest, “in phase”

43. Destructive Interference • Waves with the same wavelength but come together crest to trough • Results in waves canceling each other out, flat seas

44. Mixed Interference • Swells with varying wavelengths and wave heights come together. • Creates surf beat • Results varied sequence of high and low waves.

45. 8.5 How Do Waves Change in the Surf Zone? • Recall from the previous section - Waves are generated in the seaand move across the ocean as swell. • 1. Where do waves eventually release their energy? continental margins • 2. The area where waves break and release their energy is called the surf zone.

46. 3. As a deep-wave approaches the continental margin, the water increasingly becomes more shallow, which is called shoaling. • 4. At what point does the deep-water wave become a transitional wave? Depth < ½ wavelength • 5. What is a sign that water may be too shallow to navigate? Breaking waves/ white caps

47. 3. As a deep-wave approaches the continental margin, the water increasingly becomes more shallow, which is called shoaling. • 4. At what point does the deep-water wave become a transitional wave? Depth < ½ wavelength • 5. What is a sign that water may be too shallow to navigate? Breaking waves/ white caps

48. 6. Describe the 4 changes in the physical properties of a wave as it transitions from a deep-water wave to a breaker. a. Wave speed decreases b. Wavelength decreases c. Wave height increases d. Wave steepness increases

50. 7. Differentiate between how each type of wave breaks. a. Waves of a swell: - develop near shore - Surf is parallel, uniform breakers b. Wind-driven waves: - Unsorted waves - Waves begin to break offshore - High-energy, rough, choppy surf • 8. At what point does a wave become a shallow-water wave? Depth < 1/20 wavelength