Waves

1
Waves
2
Waves

• Transport energy over a body of water

3
Waves Origin and Type

• Wind waves wind-generated

• Seiche pressure-generated

• Tsunami seismic-generated

• Tide gravity-generated

4
Wave Terminology

• Still water line level of ocean if it were flat
  w/o waves

• Crest highest part of wave
• Trough lowest part of wave

• Wave height (H) vertical distance between crest
  and trough

• Amplitude distance between crest and still
  water line

• ½ the wave height

• Wavelength (L) horizontal distance from each
  crest or each trough

• Or any point with the same successive point

• Steepness Height (H)/length (L)

5
Wave Parameters

• Period (T) the time it takes for two successive
  waves to pass a particular point

• Frequency (f) the of waves that pass a
  particular point in any given time period

6
Deep Water WaveMotion

• Waves transmit energy, not water mass

• Water particles move in orbits

• Diameter of orbits decrease with depth

• Particle motion ceases at ½ wavelength

7
Waves Types

• Deep Water

• H2O depth is gt1/2 wavelength

• Shallow Water

• Depth is lt1/20 wavelength

8
Orbital Motion

• When under a wave crest

• Water moves up and forward

• When under a trough

• Water moves down and back

• Thus, water particles do not move forward

• They move in circles

9
WavesVelocity

• Velocity (V) wavelength (L)/Period (T)

• For example

• If T 10 sec L 100 m

• Then 100 m/10 sec. 10 m/sec

• The longer the wavelength, the faster the wave
  travels

10
WavesGeneration

• Generated by Force

• wind or air

• Generated at storm centers

• Separation of waves by differing rates of travel
  - dispersion

• Sea Wrinkles ? ripples ? wind waves ? swells

11
WavesSize

• Factors determining size

• Fetch

• Distance wind blows over open ocean

• Speed of wind

• Wind velocity

• Duration

• Length of time wind blows

12
WavesDispersion

• Wave train a set of waves with the same
  wavelength

• Individual waves move faster than wave train

• wave dies out at front of train while new waves
  form at rear

• Wave train travels half the speed of individual
  wave

13
Wave Interference

• Combination of waves

• Build from one another Constructive

• Cancel each other Destructive

14
Shallow Water Waves
1. Swell feels bottom at depth lt ½ wavelength
2. Wave crest peaks and wave slows

• 3. Orbits progressively flatten at depth

4. Wave height (H) increases and wavelength (L)
decreases
5. Wave breaks when H/L ratio gt 1/7
6. Just above seafloor particles move in
back-and-forth motion
15
Breaking Waves
16
Breaking wavesTypes

• Depends on steepness

• Type of Breakers

(a) Spilling

• Gentle slopes

• Surf gently rolls over the front

(b) Plunging

• Moderately steep slope

• Wave curls forming a tunnel

(c) Surging

• Steep slope

• Rolls onto beach

17
WavesCharacteristics

• Refraction

• Bending of waves

• Waves approach shore at angle and drags

• Feels bottom first and slows

• Diffraction

• As waves pass through small opening, waves spread

18
Seiches

• Rise and fall of water level

• Occurs in enclosed basins and/or lakes

• Stationary point (node)

• Standing wave oscillates

19
Tsunamis

• Giant sea waves generated by earthquakes

20
TsunamiCauses

• Earthquake

• Volcanoes

• Landslides

• Meteor impact

21
TsunamiCharacteristics

• Energy passes through entire water column

• Long periods (T)

• T 10-20 min.

• Small Height (H)

• H 1-2 m

• long wavelengths (L)

• L 100-200 km

• Shallow water wave

• Deep wave base

• Travel at great speeds

• c 200 m/s

22
TsunamiCrest and Trough
23
Historical Tsunamis1883 Krakatau

• Explosive volcano
• Large landmasses fell into the ocean
• 36,000 people killed by tsunami

24
Historical Tsunamis1946 Pacific Tsunami

• Aleutian Island Earthquake
• Killed 165 people in Hawaii
• Resulted in the creation of the 1st tsunami
  warning system

25
Historical Tsunamis2004 Indonesian Tsunami

• 9.0 M earthquake
• Deadliest tsunami ever recorded
• gt260,000 people killed