Waves - 8 Flashcards
What are waves?
The undulatory motion of a water surface
What is a capillary wave?
A wave with a period less than 1/10th of a second
What is chop?
Waves with a period between 1 and 10 seconds
What are seiches?
Waves with a period between 10 minutes and 10 hours
What period do tsunamis have?
Between 10 and 60 minutes
What period do tides have?
12.4 hours to 24.8 hours
What period do internal waves have?
Anything from minutes to hours
What is celerity?
Velocity of the wave form, not the water
Why is speed an inappropriate measure?
It implies that there is a mass moving forward, however in a wave it is energy moving forward
For deep water waves, celerity =
wavelength/wave period
What is fetch?
The are of contact between the wind and the water
What does the term ‘seas’ refer to?
A term applied when the fetch has a chaotic jumble of new waves, which continue to grow until the sea is fully developed
What is wave interference?
The momentary interaction between waves as they pass through each other
What is constructive interference?
When two like portions of waves convince, creating an additive effect and larger waves
What is destructive interference?
When dislike portions of waves coincide, creating a subtractive process with smaller waves
What is a rogue wave?
An unusually large breaking wave composed of several large wave that momentarily merge
Why do longer waves travel faster than short waves?
Because speed increases as wave length increases
What is dispersion?
The sorting of waves by speed and wavelength as they leave the fetch area
What does dispersion generate?
Swell (long, low waves) that produce a regular up and down motion of the sea surface
The majority of waves on the surface are …
wind-generated
What controls size and type of wave?
- Wind velocity
- Wind duration
- Fetch
- Orignial state of the sea surface
What does the term ‘old seas’ mean?
Waves on the surface that are unrelated to current wave generation
When do fully developed seas occur?
When wave are as large as possible under current conditions
What is significant wave height?
The average wave height of the highest 1/3 of the waves present
What is significant wave height good indicator for?
Potential wave damage as taller waves have the most eroding power
How do water molecules in wave move?
In an orbital motion
- upward and forward with the crest
- downward and and back with the trough, slightly ahead of their original pattern
What is mass transport and where is it significant?
The slight forward motion of the water … significant in shallow water as it can create nearshore currents
What is wave base determined by in open water?
Internal friction and energy loss in the water
What is wave based determined by in shallow water?
Interaction between the water and the sea bottom
If water is deeper than the wave base, orbits are …
Circular
If water is shallower than the wave base, orbits are …
Elliptical
What are the three types of waves (based off water depth)?
- Deep water wave
- Intermediate water wave
- Shallow water wave
What is an intermediate wave?
When water depth is between 1/2 and 1/20 of the wavelength
What is a shallow water wave?
When water depth is less than 1/20th of the wavelength
What is wave steepness?
A ratio of wave height divided by wavelength (H/L)
When does a wave become unstable?
When wave steepness is larger than or equal to 1/7
When do waves break?
When the crest moves forward, whereas the base is half back by friction, causing the wave to increasingly lean forward and eventually collapse
What are the 3 types of breakers?
- Spilling breakers
- Plunging breakers
- Surging breakers
What is a spilling breaker?
Waves with crests that continuously spill down the front of the wave, gradually depleting the waves energy
What are plunging breakers?
Waves that collapse forward and release most of the waves energy at once as it moves across a steeper, narrow surf zone
What are surging breakers?
Low, flat waves that do no break but smoothly rise and fall against a steep beach face … energy is reflected sea ward
What is a storm surge?
A rise in sea level resulting from low atmospheric pressure associated with storms and the accumulation of water dragged shoreward by winds.
When do storm surges create the most damage?
When superimposed on a spring high tide
What are wave orthogonals or wave rays?
Imaginary lines drawn perpendicular to the wave crest, dividing the wave into a series of equal segments
Where do orthogonals converge? What does this result in?
At headlands … wave energy is concentrated - larger, more erosive waves
Where do orthogonals diverge?
In bays … smaller and weaker waves here
What is a node?
An imaginary line across the surface about which the surface oscillates
What is an antinode?
Where maximum displacement of the surface occurs as it oscillates
Where is the node located in closed basins?
In the centre
Where is the node located in open basins?
At the opening of the bay or estuary
What are internal waves?
Waves generated due to density differences above and below the pycnocline
How do internal waves compare to surface waves?
- speed is slower
- height can be greater
- stability is greater (can’t collapse easily)
- longer wavelength
- greater period (minutes rather than seconds)
What generates internal waves?
Disturbances to the pycnocline e.g. tides, flow of water masses past each other, storms, submarine landslides
How long are tsunami wavelengths?
Up to 100 metres
How fast can tsunamis travel?
Up to 760 km hr-1
What type of waves are tsunamis?
Shallow to intermediate water waves
How high are tsunamis?
Between 10-50 metres
Where do tsunamis originate from
- Earthquakes
- Volcanic eruptions
- Submarine landslides
