1. CHAPTER 8 Waves and Water Dynamics

2. Waves are visual proof of the transmission of energy across the ocean

3. Origin of waves Most waves are wind-driven
Moving energy along ocean/air interface
Wind main disturbing force
Boundary between and within fluids with different densities
Air/ocean interface (ocean waves)
Air/air interface (atmospheric waves)
Water/water interface (internal waves) – movement of water of different densities
Atmospheric Kelvin-Helmholtz waves are caused when a certain type of cloud moving horizontally one way interacts with a stream of air moving horizontally at a different speed. Eddies develop, making beautiful, unusual, curling waves of cloud.

4. Internal waves Associated with pycnocline
Larger than surface waves – up to 100 m
Caused by tides, turbidity currents, winds, ships
Possible hazard for submarines
Fig. 8.1a
Internal waves (wavelength about 2 km) which seem to move from the Atlantic ocean to the Mediterranean Sea, at the east of Gibraltar and Ceuta

5. Other types of waves Splash wave Seismic sea wave or tsunami Tides
Coastal landslides, calving icebergs
Seismic sea wave or tsunami
Sea floor movement
Tides
Gravitational attraction among Moon, Sun, and Earth
Wake
Ships

6. Wave motion Waves transmit energy by oscillating particles
Cyclic motion of particles in ocean
Particles may move
Up and down
Back and forth
Around and around
Particles in ocean waves move in orbital paths

7. Progressive waves Waves that travel without breaking Types
Longitudinal – push/pull waves in direction of energy transmission
sound
Transverse – back and forth motion
Only in solids
Orbital
Combination of longitudinal and transverse
around and around motion at interface of two fluids

8. Orbital or interface waves
Waves on ocean surface at water/air interface
Crest, trough, wave height (H)
Wavelength (L)

9. Orbital waves Wave characteristics
Wave steepness = ratio of wave height to wave length H/L
If wave steepness > 1/7, wave breaks
Wave period (T) = time for one wavelength to pass fixed point
Wave frequency = # of wave crests passing fixed location per unit of time, inverse of period or 1/T

10. Circular orbital motion
Water particles move in circle
Movement up and down and
Back and forth

11. Orbital motion
Diameter of orbital motion decreases with depth of water
Wave base = ½ L
Hardly any motion below wave base due to wave activity

12. Types of Waves dependent on interaction with bottom

13. Deep-water waves No interference with ocean bottom
Water depth is greater than wave base ( > 1/2L)
Wave speed (celerity) proportional to wavelength
Longer the wave, the faster it travels

14. Shallow-water wave Water depth is < 1/20L
Wave “feels” bottom, because water is shallower than wave base
Orbits are compressed  elliptical
Celerity proportional to depth of water
The deeper the water, the faster the wave travels

15. Transitional waves
Characteristics of both deep and shallow-water waves
Celerity depends on both water depth and wavelength

16. Wave development Most ocean waves wind-generated
Capillary waves (ripples) formed first
Rounded crests, very small wavelengths
Provide “grip” for the wind
Increasing energy results in gravity waves
Symmetrical waves with longer wavelengths

17. Wave energy Factors that control wave energy Wind speed Wind duration
Fetch – distance of uninterrupted winds

18. Maximum wave height caused by wind that is known:
Reliable measurement
Measured on US Navy tanker caught in typhoon
Wave height 34 m or 112 ft
Fig. 8.10

19. Wave energy Fully developed sea Swell
Maximum wave height, wavelength for particular fetch, speed, and duration of winds at equilibrium conditions
Swell
Uniform, symmetrical waves that travel outward from storm area
Long, rounded crests
Transport energy long distances

20. Swell
Longer wavelength waves travel faster and outdistance other waves
Wave train = group of waves with similar characteristics
Sorting of waves by their wavelengths is wave dispersion
Wave train speed is ½ speed of individual wave

21. Wave interference patterns
Different swells coming together
Constructive interference
In-phase wave trains with about the same wavelengths
Add to wave height
Rogue waves – unusually large waves
Rare but can happen and be unusually large

22. Wave interference patterns
Wave interference patterns
Destructive interference
Out-of-phase wave trains with about the same wavelengths
At least partially cancel out waves
Mixed interference
Two swells with different wavelengths and different wave heights

23. Wave height is extremely variable
~50% of all waves are less than 2 m (6-7 ft)
10-15% are greater than 6 m
Up to 15 m in Atlantic and Indian oceans
Up to 34 m in Pacific - long fetch (speed at 102 km/hr)

25. Largest rogue wave can sink largest vessels
Largest = 34 m (120 ft) high (above theoretical max)
1:1200 over 3x average height;
1: over 4x height
Waves hitting current may double height suddenly and break
Most common near strong currents, long fetches, storms
Rogue waves that rise as high as 10-story buildings and can sink large ships are far more common than previously thought, imagery from European Space Agency satellites has shown. A rogue wave is seen in this rare 1980 photo taken aboard a supertanker during a storm near Durban, South Africa. (Reuters)

26. Storm surges Large wave moving with a storm (not just hurricanes)
Low pressure above water  water level rises at center
Up to 3-4 m higher than normal
Preceded by low sea-level in front of storm
Added to increased wind waves + high tide  most damage

27. Hurricane Katrina – 2005 Record storm surge in Pass Christian, MS - ~27.8 ft

28. Waves approach shore Deep-water swell waves shoal 
Transitional waves 
Become shallow-water waves (< L/2)
Wave base “touches” sea bottom

29. Waves approach shore During transition to shallow-water waves
Wave speed and wavelength decreases
Wave height and steepness increases
Waves break
Period remains constant

30. Breakers in surf zone
Different types of breakers associated with different slope of sea floor
Spilling
Plunging
Surging

31. Spilling breaker Water slides down front slope of wave
Gently sloping sea floor
Wind “onshore”
Wave energy expended over longer distance
Wind
Onshore

32. Plunging breaker Curling crest Moderately steep sea floor
Wind “offshore”
Wave energy expended over shorter distance
Best for surfers
Wind
Offshore

33. Surging breaker Breakers on shore Steepest sea floor
Energy spread over shortest distance
Challenging for surfers

34. Wave refraction
As waves approach shore, they bend so wave crests are nearly parallel to shore
Wave speed proportional to depth of water (shallow-water wave)
Different segments of wave crest travel at different speeds

35. Sets – series from relative calm to largest waves
Interference in wave train cancel some, adds to others
Destructive interference  lull “between sets”

36. Rip currents are wave energy escaping shoreline
Stream of water returning out to sea through surf zone
Flows up to a few hundred meters offshore then dissipates

37. Wave energy distribution at shoreline
Energy focused on headland
Headland eroded
Energy dissipated in bay
Bay filled up with sediment
Fig. 8.17b

38. Tsunami or seismic sea wave
Sudden changes in sea floor caused by
Earthquakes, submarine landslides, volcanic eruptions
Long wavelengths ( > 200 km or 125 m)
Shallow-water wave characteristics (<L/2)

39. Speed proportional to water depth so very fast in open ocean
Not steep when generated (low H/L ratio)
Crest of only 1-2 ft over 16 min period
Move very fast -- up to 212 m/sec (470 mile/hr)

40. As crest arrives on shore, slows but grows in height quickly
Sea level can rise up to 40 m (131 ft) when tsunami reaches shore
Fast, onrushing flood of water rather than a huge breaker
Series of waves
Warning  initial rushing out of water from shore

41. Tsunami or seismic sea wave
Most occur in Pacific Ocean (more earthquakes and volcanic eruptions)
Damaging to coastal areas
Loss of human lives
Krakatau eruption (1883) in Indonesia created tsunami that killed more than 36,000 people
Aura, Japan (1703) tsunami killed 100,000 people
Indonesia (Dec. 26, 2004) tsunami killed over 229,000 around Indian Ocean

42. Speed of tsunami
Undersea earth-quake at 6:59 AM

43. Scale of tsunami damage on Sumatran coast in Aceh province
Landsat image before tsunami: 13-Dec. 2004
** Note sediment covered area impacted by tsunami 1-5 km inshore
Landsat image after tsunami: 29-Dec. 2004

44. Tsunami watches and warnings
Pacific Tsunami Warning Center
Seismic waves forecast possible tsunami
Issues tsunami watches and warnings
Increasing damage to property as more infrastructure constructed near shore
Evacuate people from coastal areas and send ships from harbors
Water “sucked” out before first

45. Waves as a source of producing electricity
Lots of energy associated with waves
Mostly with large storm waves
How to protect power plants
How to produce power consistently
Environmental issues
Building power plants close to shore
Interfering with life and sediment movement
Offshore power plants?

46. Wave power plant at Islay, Scotland
Fig. 8.25b

47. Ocean Literacy Principles
1.c – Throughout the ocean there is one interconnected circulation system powered by winds, tides, force of the Earth’s rotation, the Sun, and water density differences. The shape of ocean basins and adjacent land masses influence the path of circulation.
5.h - Tides, waves, and predation cause vertical zonation patterns along the shore, influencing the distribution and diversity of organisms.