### Chapter 9: Waves and Wave Dynamics

```Chapter 9: Waves and Water
Dynamics
Fig. 9-10
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

Seafloor movement


Gravitational attraction Earth, Moon,
Sun


Tsunami or seismic sea wave
Tides
Human activities
Wakes of ships
 Explosions

Progressive waves

Longitudinal


Transverse


“Push-pull”
Side-to-side or up-and-down
Orbital
Circular orbit
 Ocean surface waves

Types of waves
Fig. 9-3a
Wave characteristics

Crest, trough



Wave length
Wave height/wave length = wave
steepness


Wave height is proportional to energy
Waves break when H/L is 1/7
Wave period, frequency
Wave characteristics

Wave base is 1/2 wave length

Negligible water movement due to waves
below this depth
Fig.9-6a
Deep-water wave
Depth of water is greater than
1/2 wavelength
 Speed of wave form (celerity) is
proportional to wavelength

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
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
Three types of waves
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
Surface ocean waves



Most wind-driven
Small wind-driven waves
 Capillary waves
Larger wind-driven waves
 Gravity waves
Sea


Storm at sea creates waves
Wave energy depends on
Wind speed
 Fetch
 Duration


Chaotic mixture of different
wavelengths and wave heights
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

Wave interference



Constructive
 Wave heights increase
Destructive
 Wave heights decrease
Mixed
 Wave heights vary in wave train
(surf beat)
Interference illustrated
Fig. 9-14
Rogue waves
Fig. 9-16

Unusually large waves
Constructive interference
 Waves meet strong ocean current

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

Breakers

Spilling


Plunging


Gentle beach slope
Moderately steep slope
Surging

Abrupt slope
Wave refraction

Shoaling waves bend so wave fronts
approach a shore nearly parallel
Fig. 9-19a


Wave energy
focused on
Wave energy
dispersed over
bay
Fig. 9-19b
Wave diffraction

Wave energy
transferred
around or
behind barriers
Fig. 9-20
Wave reflection
Waves bounce back from steep
slopes or seawalls
 Reflected wave may
constructively interfere with
other waves

Standing waves



Two waves with same wavelength
moving in opposite directions
Node – no vertical movement
 Greatest horizontal movement
Antinode – greatest vertical
movement
Fig. 9-22
Tsunami or seismic sea wave

Caused by sudden changes in
volume of ocean basin
 Mainly submarine faults
 Volcanic eruptions
 Submarine landslides
Fig. 9-23a
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
Tsunami warning system
Monitor seismic activity
 Monitor changes in unusual
wave activity
 Warning


People evacuate
End of Chapter 9: Waves and
Water Dynamics
Fig. 9D
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