AQA AS Geography Coasts: Waves and Tides

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  • Created on: 22-08-13 20:19
Preview of AQA AS Geography Coasts: Waves and Tides

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Waves are created by the action of wind on the surface of the sea.
They are created by the frictional drag of wind and the transfer of energy from
the wind blowing over the sea surface.
The energy waves possess is determined by:
- Wind velocity wind speed
- Duration period of time during which the wind blew
- Fetch distance over which the wind blew
The stronger the wind, the longer it blows for and the longer the fetch, the
larger the waves will be and the more energy they will have.
Wave definitions
Wave fetch: The distance of open water over which a wave has passed. Maximum
fetch is the distance from one coastline to the next landmass, it often coincides with
prevailing wind direction (South West in the UK).
Wave crest: Highest point of a wave.
Wave trough: Lowest point of a wave.
Wave height: Distance between trough and crest.
Wave length: Distance between one crest/trough and the next.

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Why Waves Break
Wave motion is confined to a depth of one wavelength in the open sea.
Particles within the wave follow a circular orbit but do not actually change their
position greatly; it is the energy in the shape of the waveform that moves.
This orbital movement is affected by the shallowing of water and the relative rising
of the sea floor as a wave approaches the coast.…read more

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Constructive Waves
Constructive waves build beaches.
They are characterised by longer wavelengths and lower height and wave
The swash on these waves is greater than the backwash, as the spilling water
has time to percolate into the beach.
This results in sediment being added to the beach which the backwash cannot
entirely remove, producing a gentle build-up of beach material.
Destructive Waves
Destructive waves destroy beaches.
They have a steeper, shorter wavelength with more frequent waves.…read more

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Constructive Waves Destructive Waves
Lower wave height Taller wave height
Less frequent waves More frequent waves
Produces build-up of beach material Moves sediment away from the beach
Strong swash and less powerful Strong backwash and less powerful
backwash swash
Longer wavelength Shorter wavelength
Spilling breaker Plunging breaker
Destructive…read more

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Wave refraction
It is very rare for waves to approach a regular uniform coastline, as most have a
variety of bays, beaches and headlands.
Because of these features, the depth of water around a coast varies and as a wave
approaches a coast its progress is modified due to friction from the seabed,
halting the motion of waves.
As waves approach a coast they are refracted so that their energy
is concentrated around headlands but reduced around bays.…read more

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Sediment Sources and
The coastal sediment or littoral cell system is a simplified model that examines
coastal processes and patterns in a given area.
Sources of sediment at the coast include coastal erosion, the sediment transported
by rivers and the wind, the biogenic input and marine deposits transported either
along the coast by longshore drift or onshore by tide and currents from offshore
Sediments may be lost to the coastal system if they are blown inland, transported
offshore or removed by human action.…read more

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The gravitational pull of the moon and the sun creates tides on the earth.
Tides are regular rising and falling movements of the surface of the sea.
This is caused by the gravitational pull of the moon as it moves around the earth.
The moon has the greatest influence; although its gravitational pull is less than that
of the sun, it is much closer.…read more


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