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What is a wave?
A flow of energy or motion
Not a flow of water
What is needed to create a wave?
Energy has to be added to water
What happens to the energy in a wave?
Dissipates at sea
Encounters a barrier
How does water move in wind-generated waves?
Water exhibits a circular motion
A wave moves much farther than the particles of water that contribute to it
How is particle motion affected by depth?
Circular motion decreases with increasing depth
What is wavelength?
Distance from one crest to another
How deep are the effects of a wave felt?
≈1/2 the wavelength
What is generating force?
The water that comes back up
What is restoring force?
Force that brings the water back down
What is the wavelength of capillary waves?
Less than 1.7 cm
What is the restoring force of capillary waves?
Surface tension
What is the wavelength of gravity waves?
Greater than 1.7 cm
What is the restoring force of gravity waves?
Gravity
What is a crest?
The peak of a wave
What is a trough?
The bottom of a wave
What is wave height?
Distance between the crest and the trough
What is a period?
The time taken for one wavelength to pass a fixed point
The time needed to go from one crest to another
What is the steepness of a wave?
H/WL
Above what steepness do waves break?
H/WL > 1/7
What are deep-water waves?
At depths greater than 1/2x wavelength
What increases the height of deep-water waves?
Wind speed
Duration
Fetch
What is fetch?
Distance over which wind can blow uninterrupted
Usually calculated as the closest distance to land
What are progressive waves?
Generated by wind
Restored by gravity
Progress in a single direction
What proportion of waves are higher than average?
1/3
What is significant wave height?
Average height of the largest 1/3 of waves
One way to record how rough the ocean is
What is the Beaufort scale?
Used to measure how wavy the surface is
Goes from 0-12
What are rogue waves?
At least 2x significant wave height
Where are rogue waves relatively common?
Southeast coast of South Africa
What is the maximum recorded rogue wave height?
34 mHo
What is swell?
A regular pattern of waves with a long wavelength
How are rogue waves formed?
Amplification of waves created by 2 or more disturbances
When does a deep-water wave become a shallow-water wave?
When it touches bottom
When does a wave touch bottom?
When the depth is ½ the wavelength
What are shallow-water waves?
Depth is ½ wavelength or less
What are 2 types of breakers?
Spilling breakers
Plunging breakers
What are spilling breakers?
Slope is continuous and quite shallow
Energy dissipates quite slowly
Lots of foam
What are plunging breakers?
Steeper slope
Sudden breaking
Formation of rollers/pipelines
What are tsunamis?
Formed by earthquakes
Only happens when an earthquake results in a vertical shift in depth
Long wavelengths
Long periods
Low height
Wave energy compressed into smaller volume near coast causes dramatic increase in height
What are tides?
Periodic changes in water level along coastlines everywhere in the world
What are the largest waves in terms of wavelength?
Tides
What is the wavelength of a tide?
The time between 2 high tides
12-24h
What are high tides?
The crests of tides
What are low tides?
The troughs of tides
Why doesn’t the sun produce tides?
It’s too far away
How are tides produced?
The Gravitational attraction of the moon and the centrifugal force of Earth’s spin creates bulges of water on opposite sides of the planet
What is a spring tide?
Really high tides
Full moon on one side and sun exactly opposite
What are neap tides?
Really low tides
Sun and moon at right angles
When are the biggest spring tides?
Equinox
When is the Equinox?
March 21st and September 21st
Most places in the world have what type of tidal cycle?
Semidiurnal
What are 3 types of tidal cycles?
Semidiurnal
Diurnal
Mixed semidiurnal
What is a semidiurnal tidal cycle?
2 low tides and 2 high tides per day
What is a diurnal tidal cycle?
1 high tide and 1 low tide per day
What type of tidal cycle do we have in British Columbia?
Mixed semidiurnal
What is a mixed semidiurnal tidal cycle?
2 high tides and 2 low tides
High tides might be different heights
Low tides might be different heights
What is a flood tide?
When the tide is coming in
What is a slack tide?
When the tide is fully up or down
No currents
What is an ebb tide?
When the tide is going out
What are amphidromic points?
Places in the world where there are no tides
No intertidal zone
Where is the largest tidal range in the world?
Bay of Fundy, New Brunswick
What is the tidal range of the Bay of Fundy?
16m
