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Chapter 9: Waves and Water Dynamics - PowerPoint PPT Presentation

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

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Fig. 9-10

• 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

• Longitudinal

• “Push-pull”

• Transverse

• Side-to-side or up-and-down

• Orbital

• Circular orbit

• Ocean surface waves

Fig. 9-3a

• 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 base is 1/2 wave length

• Negligible water movement due to waves below this depth

Fig.9-6a

• Depth of water is greater than 1/2 wavelength

• Speed of wave form (celerity) is proportional to wavelength

• 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

• 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

• 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

• Most wind-driven

• Small wind-driven waves

• Capillary waves

• Larger wind-driven waves

• Gravity waves

• Storm at sea creates waves

• Wave energy depends on

• Wind speed

• Fetch

• Duration

• Chaotic mixture of different wavelengths and wave heights

• 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

• Constructive

• Wave heights increase

• Destructive

• Wave heights decrease

• Mixed

• Wave heights vary in wave train (surf beat)

Fig. 9-14

Fig. 9-16

• Unusually large waves

• Constructive interference

• Waves meet strong ocean current

• 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

• Spilling

• Gentle beach slope

• Plunging

• Moderately steep slope

• Surging

• Abrupt slope

• Shoaling waves bend so wave fronts approach a shore nearly parallel

Fig. 9-19a

Fig. 9-19b

• Wave energy transferred around or behind barriers

Fig. 9-20

• Waves bounce back from steep slopes or seawalls

• Reflected wave may constructively interfere with other waves

• Two waves with same wavelength moving in opposite directions

• Node – no vertical movement

• Greatest horizontal movement

• Antinode – greatest vertical movement

• Caused by sudden changes in volume of ocean basin

• Mainly submarine faults

• Volcanic eruptions

• Submarine landslides

• 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

• Monitor seismic activity

• Monitor changes in unusual wave activity

• Warning

• People evacuate