1. Waves

2. Waves Waves are energy moving through a substance
a. Sometimes this movement is visible (waves on ocean surface)

3. Wave Motion Progressive Waves
Waves are a transmission of energy by cyclic movement
through a substance
The medium itself (water) does NOT travel
Wave motion is NOT water FLOW, but is a flow of energy
Progressive Waves
Are waves in which the waveform can be observed to travel
Can be longitudinal (push-pull), transverse (side to side), or
orbital (interface waves)
Orbital waves are the most common type at the sea surface
Transmit energy along the interface of two fluids of different
density (water and air)

5. Wave Characteristics
Height (H) - distance between the crest and trough
Wavelength (L) - distance between 2 successive crests or troughs
Steepness - the ratio of wave height to wavelength (H/L)(slope)
Period (T) - time for one full wave to pass a fixed point
Speed (S) - the wavelength divided by the period (L/T)
Frequency (f) - the number of wavelengths that pass a fixed point per
unit time (1/T) and S = L*f

6. Waves Waves are energy moving through a substance
a. Sometimes this movement is visible (waves on ocean surface)
Waves are formed by some “disturbing force” – and weakened by a “restoring force”

8. Waves Waves are energy moving through a substance
a. Sometimes this movement is visible (waves on ocean surface)
Waves are formed by some “disturbing force” – and weakened by a “restoring force”
3. The depth of the water changes the behavior of the wave

9. (transitional)
Wind waves in deep water:
Period – up to 20seconds
Wavelength – as much as 2000 feet (though ususally less)
Speed – up to 70mph (though usually less)
Seismic waves
Period – up to 20 minutes
Wavelength – 125 miles
Speed – around 470mph
---- longer wavelengths usually move faster.
---- In deep water, speed is directly proportional to wavelength

10. Waves Waves are energy moving through a substance
a. Sometimes this movement is visible (waves on ocean surface)
Waves are formed by some “disturbing force” – and weakened by a “restoring force”
The depth of the water changes the behavior of the wave
Wind is a common disturbing force that generates waves
transfer of wind energy into water
small amounts of energy produce small waves known as ‘capillary waves’ – rippling of water
larger energy produces “wind waves” – this happens when the wavelength is > .68” (the point at which gravity – and not capillary action – is the dominant restoring force)

11. Wind waves start small but as the crest is pushed up, it interacts even more with the wind – transferring more and more energy to the wave.
Changes in pressure around the crest create a vacuum in front of it, and push it from behind.

12. Swells are long wavelength wind waves.
The wavelengths are so long that they are sometimes imperceptible.
Long wavelengths mean they move very fast.

13. Groups of swells travel in wave trains. Individual waves do
not persist. Speed is ½ that of any individual wave. (V)

14. Waves can be HUGE:
Largest wave ever recorded = 112 feet!

15. Major Factors that Increase Wave Energy
Wind Speed
Duration - amount of time that wind blows in one direction
Fetch - the distance over which wind blows in a single direction
Fully-Developed Sea - when the maximum fetch and duration are achieved for a given wind speed

16. Interference alters waves
When waves meet they interact to either add to or subtract
from one another This is “interference”.
Constructive vs Destructive interference

17. Fig 9.13 in book

18. Rogue Waves
Very rare large waves, probably due to unusual constructive interference
Most frequent downwind from islands or shoals where storm waves
encounter strong ocean currents
Very dangerous to shipping or people on the shoreline
Can be up to m tall (8 story building!)

19. Deep water waves transition to shallow water waves
and ‘break’.
As the wave approaches the shore the cyclical motion of
molecules is slowed by availability of less water space and by
friction with the bottom
Molecules on top are still cycling more rapidly and the wave
breaks as the top wave is outrunning the bottom of the wave.
Motion of molecules changes from cyclical to longitudinal

20. Surf Breaks happen approximately when wavelength:depth is 3:4
Influenced by slope, contour, composition of beach.

21. Closed orbits occur in the nearly frictionless open ocean
Open orbits occur near shore.

22. Surf Wave Refraction - bending of a wave front
Waves seldom approach a shoreline at 90° angle
Part of the wave that contacts bottom is bent or refracted
Orthogonal lines of equal energy are always bent toward
shallower water
Energy often focused on headlands
Bays receive lower, dispersed energy that may enhance sediment
deposition

23. Wave Diffraction - bending of waves around objects
Bending occurs on a smaller scale than refraction
Any point on a wave front can be a source which can propagate
in any direction

24. Storm Surge
“bulge” of water suddenly driven ashore
Usually produced by a low-pressure system (hurricane) that
creates a hill of water that moves along with the storm
As the storm approaches shore, the hill moves onshore and
causes the sea-level to rise
Can be very destructive in low-lying areas

25. Storm Surge
“bulge” of water suddenly driven ashore
Usually produced by a low-pressure system (hurricane) that
creates a hill of water that moves along with the storm
As the storm approaches shore, the hill moves onshore and
causes the sea-level to rise
Can be very destructive in low-lying areas
NOT technically a wave.

27. Tsunamis Waves caused by seismic activity such as an
earthquake, volcanic explosion, disturbance of the seafloor, etc.
Wavelengths can exceed 200 km (125 miles)
Speed is determined by water depth and can be as fast as
700 km/h (435 miles/h)
Very small surface waves at sea, but large when they reach land
The leading edge can be a trough or a crest
Usually, the water level falls before a tsunami comes ashore
Tsunami warning system in the Pacific Ocean

28. Animation of Tsunami Generation
Tsunamis
Animation of Tsunami Generation

29. Tsunami

30. Tsunamis Tsunami Warning System Waves
MSCI 210 – Chapter 8 – Waves and Tides

31. Global Ocean Wave Model
Ocean Weather Buoy

32. The Beaufort Scale and Sea State
Waves
The Beaufort Scale
and
Sea State
MSCI 210 – Chapter 8 – Waves and Tides

33. Internal Waves
Waves that travel along the density interface in the ocean
Heights may exceed 100 m (330 ft)
The greater the density gradient, the faster the wave will move
Internal waves often move along the pycnocline
May be caused by tidal forces, turbidity currents, storms, etc.
Require little energy input
Move slower than surface waves - behave like shallow-water waves

34. Power
from the
Sea