1. Chapter 9: Waves and Water
Dynamics
Fig. 9-10

2. Waves are moving energy
 Forces cause waves to move along air/water
or within water
 Wind (most surface ocean waves)
 Movement of fluids with different densities

Internal waves often larger than surface
waves
 Mass movement into ocean

Splash waves

4.  Seafloor movement
 Tsunami or seismic sea wave
 Gravitational attraction Earth, Moon,
Sun
 Tides
 Human activities
 Wakes of ships
 Explosions

5. Progressive waves
 Longitudinal
 “Push-pull”
 Transverse
 Side-to-side or up-and-down
 Orbital
 Circular orbit
 Ocean surface waves

6. Types of waves
Fig. 9-3a

7. Wave characteristics
 Crest, trough
 Wave height is proportional to energy
 Wave length
 Wave height/wave length = wave
steepness
 Waves break when H/L is 1/7
 Wave period, frequency

9. Wave characteristics
 Wave base is 1/2 wave length
 Negligible water movement due to waves
below this depth Fig.9-6a

10. Deep-water wave
 Depth of water is greater than
1/2 wavelength
 Speed of wave form (celerity) is
proportional to wavelength

11. Shallow-water wave
 Water depth is less than 1/20 wavelength
 Friction with seafloor retards speed
 Wave speed (celerity) is proportional to depth
of water
 Orbital motion is flattened

13. Transitional waves
 Water depth is 1/2 to 1/20 of
wavelength
 Characteristics of deep and
shallow-water waves
 Wave speed (celerity) is
proportional to both wavelength
and depth of water

14. Three types of waves

15. 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

16. Surface ocean waves
 Most wind-driven
 Small wind-driven waves
 Capillary waves
 Larger wind-driven waves
 Gravity waves

17. Sea
 Storm at sea creates waves
 Wave energy depends on
 Wind speed
 Fetch
 Duration
 Chaotic mixture of different
wavelengths and wave heights

18. Wave dispersion
 Longer wavelength waves
outdistance shorter wavelength
waves
 Waves travel in groups or trains
with similar characteristics
 Swell made up of waves of
similar wavelength and period

19. Wave interference
 Constructive
 Wave heights increase
 Destructive
 Wave heights decrease
 Mixed
 Wave heights vary in wave train
(surf beat)

20. Interference illustrated
Fig. 9-14

21. Rogue waves
 Unusually large waves
 Constructive interference
 Waves meet strong ocean current
Fig. 9-16

22. Rare photo of Rogue wave off Durban, South
Africa in 1980. The tower at the front right is 25 m
above sea level during flat seas!

23. Click on Picture

24. 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 hold
wave together

25. Wave speed and length decreases
and wave height increases. When
Wave steepness reaches 1/7 the
wave will break.

26. Breakers
 Spilling
 Gentle beach slope
 Plunging
 Moderately steep slope
 Surging
 Abrupt slope

27. Spilling Breakers
 occur on beaches with gentle slopes.
 These waves break far from the shore, and the
surf gently rolls over the front of the wave.

28. Plunging Breakers
 happen on beaches where the slope is moderately steep.
 This kind of wave normally curls over forming a tunnel until
the wave breaks.
 Expert surfers love this type of wave!

29. Surging Breakers
 happen on beaches where the slope is very steep.
 The wave does not actually break. Instead, it rolls onto the
steep beach.
 These kinds of breakers are known for their destructive
nature.

30. Wave refraction
 Shoaling waves bend so wave fronts
approach a shore nearly parallel
Fig. 9-19a

31.  Wave energy
focused on
headland
 Wave energy
dispersed over
bay
Fig. 9-19b

32. Wave diffraction
 Wave energy
transferred
around or
behind barriers
Fig. 9-20

33. Wave reflection
 Waves bounce back from steep
slopes or seawalls
 Reflected wave may
constructively interfere with
other waves

34. Standing waves
 Two waves with same wavelength
moving in opposite directions
 Node – no vertical movement
 Greatest horizontal movement
 Antinode – greatest vertical movement

35. Fig. 9-22
Click on Picture to See
Surfers Riding Standing
Waves

36. Tsunami or seismic sea wave
 Caused by sudden changes in
volume of ocean basin
 Mainly submarine faults
 Volcanic eruptions
 Submarine landslides

37. Fig. 9-23a

39. Tsunami
 Very long wavelength
 Travels fast
 Raises sea level as crest shoals
 Trough causes sea level to fall
 Disastrous for infrastructure at
coasts
 Possibly much loss of life

40. Tsunami warning system
 Monitor seismic activity
 Monitor changes in unusual
wave activity
 Warning
 People evacuate

41. End of Chapter 9: Waves and
Water Dynamics
Fig. 9D