Geography- Coasts

About the topic Coast for AQA Geography A

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  • Created by: Sam
  • Created on: 06-06-12 17:25

Waves

  • Waves are usually formed because friction of the wind blowing over the sea causes ripples in the surface tension.
  • The further the fetch the stronger the wave.
  • As waves approach the shore the rising seabed disrupts the circular motion of the wave so that the top of the wave moves faster until the wave breaks.
  • Water up the beach= swash, Water back down the beach= backwash

There are two types of waves:

Constructive- Swash more powerful than backwash. Well spaced apart and powerful, they carry a lot of sediment to build up a beach

Destructive- Baskwash more powerful than swash. Larger in height than constructive waves and more often. They remove sediment instead of building it up.

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Land processes that shape the coastline

Weathering- effects rocks exposed at the coast e.g. freeze-thaw weathering effects cliffs (which can cause rock falls)

Mass movement

Downhill movement of material due to gravity

Rock fall- fragments of rock break away from cliff face

Landslide- blocks of rock slide down hill (on a slope)

Mudflow- saturated soil and weak rock flows down slope

Rotational slip- slump of saturated soil and weak rock along a curved surface. The result looks kind of like steps.

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Marine processes that shape our coastline

Erosion
Hydraulic power- trapped air blasted into holes in rock due to force of waves
Corrasion- fragments of rock hurled at cliff by sea
Abrasion- 'sandpaper' effect of pebble grinding over a rocky platform
Solution- some rocks can be dissolved by sea water e.g. Chalk
Attrition- Rock fragments knock against each other causing them to become rounded

Trasportation
Solution- dissolved chemicals
Suspension- Particles carried within the water
Traction- large pebbles rolled along the seabed
Saltation- pebbles just to large to be suspended 'bounce'
Longshore drift- Sediment moved along a strech of coastline due to waves approaching the beach at an angle

(Deposition also effects the coastline)

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Erosional Landforms

Headlands and Bays- when bands of soft and hard rock are perpendicular to the coast the hard rock erodes slower so it stick out to form the headlands.

Cliffs- when waves break against a cliff they slowly erode it forming a wave-cut notch. Over a long period of time the notch gets deeper until the cliff collapses. The process repeats and the cliff line gradually retreats leaving a wave-cut platform behind.

Cave- weaknesses in a headland are more vunerable to erosion and eventually the sea will gouge them out to form a cave.

Arches- over time erosion may lead to two back to back cliffs breaking through to form an arch.

Stack- gradually the arch weakens until the top caves in leaving a stack standing out to sea. The stack is then undercut until only a stump remains which will to erode.

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Depostional Landforms

Beaches- accumulations of materials found where deposition occurs. Bays usually have sandy beaches and pebble beaches are most commonly found where cliffs are being eroded. Ridges in pebbles beach are common and show high tide levels.

Spits- a spit is a long narrow strip of sand or shingle jutting out into the sea. Formed by LSD they extend out into the sea at sharp changes in the direction of coastline. Furthur away from the coast the spit gets effected by different wave directions and get get a curved end. Saltmarshes can form in the area trapped behind a spit providing an important habitat for plants and birds.

Bars- occasionally LSD might cause a spit to grow right across a bay trapping a freshwater lake behind it. This type of feature can be called a barrier beach as it protects the Lagoon behind.

Tombolo- where an spit extends to join an Island to the mainland.

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Rising Sea Levels

The biggest effect of sea level rise will be flooding. Low land areas such as in East Anglia will be at risk. Salt marsh habitats could be destroyed, agricultural land and settlements could be lost.

Rates of erosion could also increase putting even more risk to areas of land.

This being said rates of erosion will vary from place to place.

The main cause of sea level rise is thought to be is thermal expansion of sea wateras it absorbs more heat from the atmosphere. Melting of ice on land will also contribute.

Already two Pacific Islands have been submerged.

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How coastlines can be managed

Hard engineering- using artifical structures to control the forces of nature

Sea wall- Concrete or Rock barrier to the sea the reflects waves back into the sea. Can cost up to £6 million per kilometre
Groynes- Timber or Rock built perpendicular to the coastline that trap beach sediment £10,000 each but interupts longshore drift with negavtive effects further down the coastline.
Rock Armour- Piles of large boulders dumped at foot of cliff to absorb the impact of the waves. Approx. £1,000 to £4,000 per metre but cheap to maintain

Soft engineering- fit in with natural processes

Beach nourishment- Addition of sand to an existing beach but will need repeating
Dune regeneration- Planting marram grass to stablise dunes but can be damaged.
Managed retreat- allowing areas to flood. Conpensation has to be paid to those who lose land but it doesn't cost much in the long run

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Comments

:) PurpleJaguar (: - Team GR

Really good notes thanks! :P

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