GCSE Geography

GCSE Geography A - The Coastal Zone


Weathering Processes

Igneous rock - formed from magma, e.g. granite
Sedimentary rock - formed from compressed sediment, e.g. limestone
Metamorphic rock - formed under pressure, e.g. marble

  • Physical Weathering
    Freeze-thaw occurs when cracks in rocks are filled with water when it rains and as tempratures drop below freezing at night in places such as the desert, the water freezes and expands putting pressure on the surrounding rock. Over time this is repeated until the rock breaks apart.
  • Chemical Weathering
    Carbonation occurs when excess CO2 in the atmosphere is absorbed by the rain and when it precipitates this water runs over rocks such as limestone which reacts with the water and some of the chemicals in the rock are carried away in solution.
  • Biological Weathering
    This occurs when the roots of strong plants and trees penetrate the joints and bedding planes in rocks and expand them as they grow.
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Erosion Processes

1) Abrasion
'Sandpapering' effect of small pebbles against cliffs
Can cause exfoliation of a rock face to become smooth

2) Attrition
Fragments of rock being transported by waves crash against each other
This causes them to wear away or break

3) Hydraulic Power
The force of waves crashing into wave-cut notches and faults in cliffs
Air gets compressed, and then released again with explosive power

4) Solution
Chemicals in some rocks get dissolved by the water
E.g. limestone and chalk, which both contain calcium carbonate

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There are 2 types of waves:

1) Constructive

  • Has a larger swash than backwash
  • Are formed in calm weather conditions
  • Waves are long, and short in height
  • They deposit beach material, as they have enough energy in the swash to transport it up the beach but not enough energy in their backwash to remove it again

2) Destructing

  • Larger backwash than swash
  • Formed in storms or high winds out at sea
  • Waves are high, and break and foam
  • They remove beach material as the backwash has enough energy to do so, but the swash does not have enough energy to deposit
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1) Traction - Large rocks are rolled along the sea floor by waves
2) Saltation - Medium sized pebbles are bounced along the sea floor
3) Suspension - Small pebbles are suspended in the water
4) Solution - Minerals are dissolved in the water

Longshore Drift:

  • Waves travel up the beach at an oblique angle and carry sediment
  • This is pulled back by the back wash so created a zigzag pattern
  • This repeated motion causes sediment to be transported along the coast

Mass Movement:

  • Sliding - rocks, soil and other loose material slide rapidly down a slope
  • Slumping - a mass of soil or clay rotates downwards, virtually intact, down a slip-plane
  • BOTH are due to excessive rainfall
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Erosion Landforms

Headlands and Bays

  • Headland - land that juts out into the sea
  • Bay - a curved coastal inset

1) Less resistant rock (e.g. clay) is eroded away quickly by the sea

2) More resistant rock (e.g. chalk/limestone) is eroded away more slowly

3) The refraction of waves round the coastline causes waves to lose energy as they dissipate at the bays, which results is deposition to form a beach

4) Wave energy is concentrated at the headland due to refraction

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Erosion at Cliffs

1) Waves erode the base of the cliff between the low-tide mark and the high-tide mark to form a wave-cut notch

2) The cliff above the wave-cut notch is not supported and gravity becomes too much and it breaks and falls into the sea

3) The cliff is broken up and eroded by the sea by attrition and abrasion into smaller rocks and pebbles

4) These rocks contribute to the exfoliation of the rock on the bottom of the wave-cut notch by abrasion. This results in a smooth wave-cut platform.

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Erosion at Headlands

1) Faults in the joints of the cliffs are eroded to form small cracks

2) These cracks are eroded further by hydraulic power to form caves (or wave-cut notches)

3) This happens on either side of the headland due to the concentration of waves refracted round the coast

4) Caves on both side of the headland eventually meet to form a hollow arch

5) The top of the arch is eroded by precipitation, such as acid rain, and other forms of weathering

6) This eventually falls into the sea, leaving a stack of isolated cliff

7) This is also weathered down to leave a stump

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Deposition Landforms

1) Berms
Ridges of sand or shingle deposited at high tide
Deposited by the swash of constructive waves
The waves do not reach high tide again to remove it
The larger the beach material, the higher up the beach a berm is forms

2) Spits
Formed when there is a sudden change in direction of the coastline
Longshore drift continues and carries the beach out to sea
Spits often form in front of a river mouth
A salt marsh is created when the sea water and freshwater meet behind the spit
A hooked end develops when the wind changes direction

3) Bars
Formed when a spit travels across a bay for join two headlands
A lagoon forms behing the bar, an area with low wave energy
Sometimes the bar is pushed back to form a barrier beach

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Sea Level Rise

  • Sea levels have risen 40cm in the past 140 years
  • By 2100 it is estimated that it will have risen another 60cm
  • The main two reasons for this are:

1) As global warming causes tempratures of the sea to rise, the warmth spreads to the depths of the ocean and the sea expands and this causes sea levels to rise. This will continue as global warming continues.

2) Global is increasing tempratures in polar regions faster than anywhere else in the world. This is causing the ice sheets covering Antartica and Greenland to melt and this is causing sea levels to rise.

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Hard Engineering

  • Sea Wall - high concrete walls with a curved face that deflects wave energy 3-5m tall.
    This is effective, and provides a promenade for locals and tourists.
    However it is very expensive and needs constant maintenance, and can be seen as aesthetically obtrusive.
  • Groynes - wood or rock built perpendicular to the coast to trap sediment deposited by longshore drift.
    They are effective and result in a bigger beach, which benefits the tourism industry
    However they result in increased rates of erosion further down the coast.
  • Rock Armour -  Large boulders placed as the base of cliffs to absorb wave energy
    They are easy to maintain and can be used for fishing.
    However they have to be brought onshore by barge and this is very expensive. They do not fit in with the natural geology of the area so can look unnatural and unpleasant.
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Soft Engineering

  • Beach Nourishment - Addition of sand or shingle to a beach, brought onshore by barge.
    This blends in with the natural beach material, and will result in a bigger beach which will increase tourism to the area.
    However this needs constant maintenance.
  • Dune Regeneration - Marram grass planted to stabilise dunes.
    This is relatively cheap and increases the areas biodiversity.
    However the grass needs time to grow so the beach has to be sectioned off and this is very time consuming.
  • Managed Retreat - Allowing low lying areas to be flooded to create marshes.
    This is relatively cheap and increases the areas biodiversity.
    However land is lost during this, and any residents or industries forced to move will need compensation.
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