Coastal processes 8.1 Flashcards
What is a coast and what is another name for it?
A narrow zone where the land and sea interact
Also called the littoral zone.
What are the four coastal inputs?
- Atmospheric
- Marine
- Land
- Human activity
What are the two coastal processes?
- Marine action: processes that happen because of the action of the waves & tides, at the base of cliffs or beaches.
- Subaerial action: processes that happen to break down and remove rock above the reach of the waves & tides.
What are the four coastal outputs?
- Landforms of erosion: headlands
- Depositional deposition: spits
- Landforms of emergence: fjords
- Landforms of submergence: raised beaches
What are berms, runnels & cusps?
Berms - shingle ridges often found towards the back of a beach
Runnels - depressions between intertidal bars
Cusps - shoreline formations made up of various grades of sediment in an arc pattern
What is a wave and how is wave direction determined?
- A wave is the movement of energy through water and is caused by the frictional drag of the wind as it blows across open water.
- As waves form, the surface becomes rougher and it is easier for the wind to grip the roughened water surface which intensifies the size of the waves.
- Wave direction is a reflection of wind direction.
The size and energy of a wave depends on which 3 factors?
- Wind speed.
- Length of time that the wind blows.
- Length of fetch - a distance of the sea.
Define:
- Wave crest.
- Wave trough.
- Wave height.
- Wavelength.
- Wave period.
- Wave velocity.
- Wave frequency.
- Wave crest - top of the wave.
- Wave trough - lowest point between two wave crests.
- Wave height - difference between height of crest and trough.
- Wave length - distance between two crests.
- Wave period - time taken for one wavelength.
- Wave velocity - speed of movement of the crest.
- Wave frequency - number of waves that break in a given time.
What happens when a wave reaches shallower water?
- As the base of the wave slows down, circular oscillation becomes more elliptical (rugby ball-shaped).
- As the wave moves into shallower water the wave steepness increases and the wavelength decreases until the upper part spills or plunges over.
What is the plunge line, swash, and backwash?
- plunge line: point at which wave breaks
- swash: body of foaming water which rushes up the beach
- backwash: any water returning to sea
- the area where swash and backwash occurs is called the swash zone
Describe destructive waves.
- Often described as plunging or surging
- They are tall in height and have a short wavelength (20m) (high in proportion to their length)
- They break frequently at a rate of 10-15 per min
- Backwash is more powerful than swash
- Therefore it erodes sediment from the beach and there is little deposition onto the beach
- This scours away the beach, creating a steep beach angle and an offshore bar
Describe constructive waves.
- Often described as spilling or collapsing
- They are small in height and have a long wavelength (up to 100m)
- They break infrequently at a rate of 10 or less per min
Swash is more powerful than backwash - Therefore it deposits sediment onto the beach and there is little erosion/scouring of the beach
- This builds up the beach, creating a gently sloping beach angle leading to the formation of berms on sandy beaches
What are the three types of breaking waves?
Spilling breakers
Plunging breakers
Surging breakers
Breaking waves: spilling
- Spilling breakers occur on gently sloping beaches where waves break slowly over a long distance
- The waves are steep (high height compared to length)
- Gradual peaking of the wave occurs until it is unstable
- The crest spills gently down the front of the wave
Breaking waves: plunging
- Plunging breakers are found where the coast is a little steeper.
- The waves slow down more quickly than for spilling
- The crest curls way over the front of the wave and plunges down towards the base as an in tact mass of water
- It is a good surfing wave- Hawaii.
