Marine processes and waves Flashcards
How do waves happen?
Waves are caused by friction between wind and water transferring energy from the wind into the water. The force of wind blowing on the surface of water generates ripples, which grow into waves when the wind is sustained.
In terms of waves, what happens in open sea?
Waves are simply energy moving through water.
The water itself only moves up an down, not horizontally.
There is some orbital water particle motion within the wave, but not net forward water particle motion.
On what factors does wave size depend on?
The strength of the wind
The duration the wind blows for
Water depth
Wave fetch
What is fetch?
Fetch is the uninterrupted distance across water over which a wind blows, and therefore the distance waves have to grow in size.
Process of a wave as it nears the coast
At a water depth of approximately half the wavelength, the internal orbital motion of water within the wave touches the sea bed.
This creates friction between the wave and the sea bed, and this slows down the wave.
As waves approach the shore, wavelength decreases and wave height increases, so waves ‘bunch’ together.
The wave crest begins to move forward much faster than the wave trough.
Eventually the wave crest outruns the trough and wave topples forward (brakes).
Features of a constructive wave
Have a low wave height (less than 1m) and long wavelength (up to 100m)
‘Flat’ waves with a strong swash but weak backwash.
Have strong swash that pushes sediment up the beach, depositing it as a ridge of sediment (berm) at the top of the beach.
Have a backwash that drains into the beach sediment.
What is swash?
Swash is the flow of water up the beach with a breaking wave.
What is backwash?
Backwash is the water draining down the beach back into the sea. Both can transport sediment.
Features of a destructive wave
Have a wave height of over 1m and wavelength of around 20m.
Have a strong backwash that erodes beach material and carries it offshore, creating an offshore ridge or berm.
What does beach morphology mean?
Beach morphology means the shape of a beach, including its width and slope (the beach profile) and features such as berms, ridges and runnels.
It also includes the type of sediment (shingle, sand, mud) found at different locations on the beach.
How can beach morphology change in the course of a year?
Over a day, as a storm passes and destructive waves change to constructive ones as the wind drops.
Between summer and winter
When there are changes to climate e.g, if global warming resulted in the UK climate becoming on average stormier, then destructive waves and ‘winter’ beach profiles would become more common.
Which landforms on beaches change constantly?
Storm beaches, high at the back of the beach, result from the high energy deposition of very coarse sediment during the most severe storms.
Berm ridges, typically of shingle/gravel result from summer swell wave deposition.
Low channels and runners between berms.
Offshore ridges/bars formed by destructive wave erosion and subsequent deposition of sand and shingle offshore.
