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Summary Full A Level Coasts Revision Notes - AQA, OCR
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Full content of the A level Geography Course (Coast Element), is extremely helpful for individuals studying AQA or OCR Geography.
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Coast Mock Revision NotesThe coast is an open system – this means energy and matter can be transferred
from neighbouring systems as an input as well as an output.
A coastal landscape has:
1. Input- Energy or Material; moving into the system from the outside,
which drives the systems. E.g. energy (kinetic, thermal, potential) and
sediment)
2. Output- Including marine and wind erosion from beaches and rock
surfaces; evaporation. E.g. evaporation, erosional landforms, depositional
landforms
3. Throughputs- Processes such as erosion, weathering and deposition. E.g.
erosion, weathering, deposition, transportation, evaporation and longshore
drift
4. Stores- Including beach and near shore sediment accumulation.
Equilibrium – when the systems input and outputs are equal. The sediment
added to the beach is equal to the rate being removed.
Dynamic equilibrium – when the equilibrium is disturbed so the system
undergoes self-regulation and changes its form in order to restore the
equilibrium.
Negative feedback – when a change in the system causes other changes that the
opposite effect. E.g. As a beach erodes; the cliff is exposed to the waves. Sediment
eroded from the cliff is then deposited on the beach, causing it to grow in size
again. This is good.
Positive feedback- This is when a change in the system causes other changes
that have similar effects. E.g. If a beach starts to form it slows down waves, which
cause more sediment to be deposited, increasing the size of the beach. This is
bad.
Sediment Cells
A sediment cell is a stretch of coastline and its associated nearshore area within
which the movement of coarse sediment, sand and shingle is largely self-
contained. They are regarded as closed systems and there are 11 large sediment
cells in England and Wales.
Sources of Sediment
, 1. Terrestrial- Major sources of sediment come from river (80%) and also
from cliff erosion of weathering.
2. Offshore- Sediment can be transferred by waves, tides and currents from
sandbars and the seabed.
3. Wind- Windblown sand can be deposited in coastal environments
especially from deserts.
4. Human action- Sediment can be added to a coastal environment via
beach nourishment
5. Biogenic input- E.g. Shells.
Influences on the Coastal Landscape
Winds
The source of energy for coastal erosion and sediment transport is wave action.
The wave energy is generated by the frictional drag of wind moving across the
ocean surface.
Waves
A wave possesses potential energy as a result of its position above the wave
trough, and kinetic energy caused by the motion of the water within the wave.
The waves energy depends on:
1. Wind velocity
2. Duration (period of time which the wind blows)
3. Fetch (distance over which the wind blew)
Breaking waves
When waves move into shallow water their behaviour changes. The deepest
circling water molecules come into contact with the seafloor. Friction between
the seafloor and the water change the speed, direction and shape of the wave.
Then the wave slows down, the wavelength decreases, then the waves topples
over and breaks against the shore. There are three different types of breaking
waves:
1. Spilling waves- Steep waves breaking onto gently sloping beaches, water
spills gently forward as the wave breaks
2. Plunging waves- Moderately steep waves breaking onto steep beaches,
water plunges vertically downwards as the crest curls over.
3. Surging waves- Low-angle waves breaking onto steep beaches, the wave
slides forward and may not actually break.
, Swash – water moving up the beach which decreases in speed the further it
travels.
Backwash – the return of water back down the beach as a result of gravitational
pull
Constructive vs. Destructive Waves
Constructive:
o Low waves and long lengths
o Low frequency
o Strong swash (spilling waves)
o Constructs the beach
Destructive:
o High waves and short lengths
o High frequency
o Weak swash and strong backwash (plunging wave)
o Destroys beaches.
Wave Refraction
When wave approach an irregular coastline they are refracted.
For example when a wave approaches a headland, parts of the wave will be
slowed down by frictional contact, the waves therefore get higher and steeper
and the velocity decreases leading to a shorter wavelengths.
This therefore leads to wave energy being concentrated on the headland.
Tides
Tides are caused by the gravitational pull of the sun and moon on the oceans,
through the moon has the greatest influence because it is nearer the earth. Two
important aspects of tides are:
o Tidal frequency
o Tidal range (distance between low and high tide)
The moon pulls water towards it creating a high tide
When the moon and sun are in line it is when gravitational pull peaks, causing a
spring tide, which is a higher high tide and a lower low tide.
When the moon and sun are at right angles this creates a neap tide, which are a
low high tide and a high low tide (low tidal range)
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