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 Tsunami or seismic sea wave Gravitational attraction Earth, Moon, Sun Tides Human activities Wakes of ships Explosions

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

Types of waves Fig. 9-3a

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

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

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 Gentle beach slope Plunging 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 headland 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