Geography- The coastal Zone

AQA specification A, The coastal zone unit 1B

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Coastal Weathering

Mechanical weathering is the breakdown of rock without changing its chemical composition- freeze thaw weathering affects the coasts:

  • it happens when the temperature alternates above and below 0'C
  • water gets into a rock with cracks e.g. granite
  • when the water freezes it expands- putting pressure on the rock
  • when the water thaws it contracts- releases pressure
  • repeated freezing and thawing widens the crack and causes the rock to break up

Chemical weathering is the breaking down of rock by changing its chemical composition. Carbonation weathering happens in warm and wet conditions:

  • when the coastline comes in contact with acid from the rain and salt from seawater it causes the rock to react with it which makes them break down

Biological weathering occurs on the rock face, it eventually results in erosion of the rock when plants grow inside the cracks forcing them open

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Mass Movement

Mass movement is the shifting of rocks and loose material down a slope e.g. a cliff, it happens when the force of gravity acting on a slope is greater tan the force supporting it

More likely to happen when the material is full of water as it acts as a lubricant

rapid, dry movements= avalanches or cliff collapse

slow, wet movements= landslip or landslides

slumping occurs when:

  • rainwater seeps through sand which lies above the clay and saturates the base sand layer along the junction with the clay- cause shifts with rotation

slides- material shifts in a straight line

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Processes of Erosion

Hydraulic power:

  • waves crash against rock and compress air in the cracks, putting pressure on the rocks, it exploits cracks in cliff faces weakening the rock

Abrasion:

  • erodes the coastline by throwing pebbles, sand and small rocks at the cliff race which removes small pieces and makes it weaker

Attrition:

  • eroded particles in the water smash into each other and break into smaller fragments, they weaken and wear down forming sand

Solution/Corrosion:

  • weak carbonic acid in seawater dissolves rock like chalk and limestone
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Destructive Waves

Destructive waves carry out the erosional processes

  • have high frequency (11-14 waves per minute)
  • they are high and steep
  • their backwash (movement down the beach) is more powerful than their swash (the movement up the beach)- meaning that material is removed
  • the heigh and strength of waves depends on:
    • speed of wind
    • time the wind blows for
    • length of water wind blown over
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Wave-cut platforms

  • e.g. Beachy head in Sussex
  • Waves cause most erosion at the foot of a cliff
  • This forms a wave-cut notch, which is enlarged as erosion continues
  • the rock above the notch becomes unstable and eventually collapses
  • the collapsed material is washed away and a new wave-cut notch starts to form
  • repeated collapsing results in the cliff retreating
  • A wave-cut platform is the platform that's left behind as the cliff retreats
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Diagram of wave-cut platform

(http://www.geographylwc.org.uk/gcse/year5/5coast/cliffs.jpg)

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Headlands and Bays

  • some types of rock are more resistant to erosion than others
  • Headlands and bays form where there are alternating bands of resistant and less resistant rock along a coast
  • the less resistant rock (e.g clay) is eroded quickly and this forms a bay- bays have a gentle slope
  • The resistant rock (e.g. chalk) is eroded slower  and its left jutting out- forming a headland, they have steep sides
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Caves, Arches and stacks

  • Headlands are usually made of resistant rocks that have weaknesses like cracks
  • Waves crash into the headlands and enlarge the cracks- mainly by hydraulic power and abrasion
  • Repeated erosion and enlargement of the cracks causes a cave to form
  • continued erosion deepens the cave until it breaks through the headland forming and arch e.g. Durdle Door in Dorset 
  • Erosion continues to wear away the rock supporting the arch, until it eventually collapses
  • This forms a stack an isolated rocks that's separate from the headland e.g. old harry in Dorset
  • Weather and sea attack the stack and leave behind a stump that is covered by high tide
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Diagram of arch and stack formation

(http://onlinegeography.wikispaces.com/file/view/Arch_and_Stack_formation.jpg/157619991/Arch_and_Stack_formation.jpg)

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Longshore drift

Material is transported along coasts by longshore drift

  • waves follow the direction of the prevailing wind
  • they approach the coast at angle (cannot be a right angle)
  • the swash carries material up the the beach in the same direction as the waves
  • the backwash carries the material down the beach at right angles and back towards the sea
  • material zig zags along the coast

(http://www.revisionworld.co.uk/files/longshore.jpg)

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Processes of transportation

Traction-

  • large particles like boulders are pushed along the sea bed by the force of the water

saltation-

  • pebble-sized particles are bounced along the sea bed by the force of the water

suspension-

  • small particles like silt and clay are carried along in the water

solution-

  • soluble materials dissolve in the water and are carried along
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Deposition

Deposition is when material being carried by sea water is dropped on the coast

Coasts are built up when the amount of deposition is greater than the amount of erosion

the amount of material that's deposited on an area of coast is increased when:

  • there's lots of erosion elsewhere on the coast so there's lots of material available
  • there's lots of transportation of material into the area

low energy waves (i.e. slow waves) carry material to the coast but they're not strong enough to take a lot of material away- this means there's lots of deposition and very little erosion

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Constructive waves

Constructive waves deposit more material than they erode

  • have a lower frequency (6-8 waves per minute)
  • they are low and long
  • the swash is powerful and it carries material up the coast
  • the backwash is weaker and it doesn't take a lot of material back down the coast- means that material is deposited on the coast
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Formation of Beaches

Beaches are found on coasts between the high water mark (highest point on the land the sea gets to) and the low water mark (lowest point on the land the sea gets to)

They are formed by constructive waves depositing sand and shingle

Characteristics of sandy beach:

  • flat and wide
  • sand particles are small and the weak backwash can move them back down the beach creating long gentle slopes

Characteristics of a shingle beach:

  • steep and narrow
  • shingle particles are large and the weak backwash can't move them back down the beach, shingle particles build up and create a steep slope
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Spit formation

Spits are beaches that stick out into the sea, they are joined to the coast at one end, if a spit sticks out and connects with another bit of mainland, it'll form a bar.

Long and narrow ridge of sand or shingle e.g. Hurst castle spit, spurn point

Spits:

  • spits form at sharp bends in the coastline e.g. at the river mouth
  • longshore drift transports sand and shingle past the bend and deposits it in the sea
  • strong winds and waves can curve the end of the spit (recurved end)
  • the sheltered area behind the spit is protected from waves- lots of material accumulates in this area meaning plants can grow there
  • frequently found where coasts change direction and at mouths of rivers and estuaries
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Formation of Bars

A bar is formed when two headlands join together e.g. Slapton in Devon

  • bar cuts off the bay between the headlands from the sea
  • this means a lagoon can form behind the bar e.g. Loe in Cornwall
  • need water to have large load, bend in the coastline
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Tombolos

Tombolos are similar to spits but link mainland to an offshore island e.g. chesil beach in Dorset

requires:

  • south west prevailing winds
  • very long fetch
  • high energy waves
  • shingle beaches links coastline to the isles of Portland
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Identifying Landforms caused by erosion

Caves, Arches and Stacks:

  • caves and arches can't be seen as there is rock above them
  • stacks and stumps look like little blobs in the sea

Cliffs and wave cut platforms:

  • cliffs are shown on maps as little black lines
  • wave-cut platforms are shown as bumpy edges along the coast
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Identifying landforms caused by deposition

Beaches:

  • sand beaches are shown on maps as pale yellow
  • shingle beaches are yellow or white with speckles

Spits:

  • Spits are shown by a beach that carries out to sea, but is still attached to the land at one end
  • there might also be a sharp bend in the coast that caused it to form
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Causes of sea level rise

  • Global sea level is rising at a rate of about 2mm a year- increased by about 20cm over past century
  • the cause is global warming because of the rapid rise in global temperature
  • global warming has 2 effects that cause the sea level to rise
  • Melting ice:
    • the melting of ice on the land (e.g. the Antarctic ice sheet) causes water that's stored as ice to return to the oceans
    • this increases the volume of water in oceans and causes sea level to rise
  • Heating oceans:
    • increased global temperatures to get warmer and expand (thermal expansion) this increases volume of water causing levels to rise
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Rising Sea level increases coastal flooding

Coastal flooding will become more common and cause more damage especially in low lying parts of the world like the Maldives and Bangladesh, the impacts:

Economic:

  • loss of tourism- many coastal areas are popular tourist destinations. flooding can cause tourist attractions to close and it can put people off
  • damage repair- can be extremely expensive
  • loss of agricultural land- sea water has a high salt content. salt reduces soil fertility, so crop production can be affected for years after

Social:

  • deaths- coastal floods have killed thousands
  • water supplies affected: can pollute drinking water with salt or sewage
  • loss of housing- leave people homeless
  • loss of jobs- coastal industries may be shut down because of damage to equipment and buildings e.g. fishing boats
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Impacts of Coastal flooding

Environmental:

  • Ecosystems affected: seawater has a high salt content, increased levels of salt can damage or kill organisms in an ecosystem
  • Vegetation Killed by water: the force of floodwater uproots trees and plants. standing flood water also drowns trees and plants
  • Increased erosion: a large volume of fast-moving water can erode lots of material and erode the environment

Political:

  • the government has to rake policies to reduce the impacts of future flooding,
  • they do this by building more or better flood defences or they can manage the use of the area that might be flooded e.g. stopping people living there
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Case Study, Coastal Erosion- The Maldives

Population: about 300,000 people

number of islands: 1190, only 199 are inhabited

average island height: 1.5m above sea level- 80% of the land is below 1m. because of rising sea levels scientists think the islands will be submerged within 50 to 100 years

Impacts on the Maldives:

Economic:

  • Loss of tourism- tourism is the largest industry in the Maldives, if the main airport can't work properly because of  coastal flooding the country will be cut off from international tourists. this will massively reduce the country's income
  • Disrupted fishing industry- fish are the Maldives' largest export. Coastal flooding may damage fish processing plants, reducing fish exports and the country's income
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Case Study, Coastal Erosion- The Maldives

Social Impacts:

  • Houses damaged or destroyed- severe flood can leave entire communities homeless
  • less freshwater available- supplies of freshwater are already low on many of the islands. If supplies are polluted with salty seawater during floods, then some islands will have to rely on rainwater or build expensive desalination plants to meet their water demands

Environmental:

  • loss of beaches- coastal flooding wears away beaches on the islands at a rapid rate. this destroys habitats and exposes the land behind the beach to effects the flooding
  • loss of soil- the soil on most of the islands is shallow (about 20cm deep or less)  coastal floods could easily wash away the soil layer, which would mean most plants won't be able to grow
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Case Study, Coastal Erosion- The Maldives

Political:

  • The Maldivian Government had to ask the Japanese Government to give them $60 million to build the 3m high sea wall that protects the city, Male
  • Changes to environment policies- increased flooding is caused by rising sea level, which is caused by global warming
  • the Maldives has pledged to become carbon neutral so it doesn't contribute to global warming, they are encouraging other governments to do the same
  • Changes to long-term plans- the government is thinking about buying land in countries like India and Australia and moving most Maldivians there, before the islands become uninhabitable
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Case Study, Coastal Erosion- Holderness

The holderness coastline is 61km long- it stretches from flamborough head (a headland) to Spurn Head (a spit)

Erosion is causing the cliffs to collapse along the coastline, the material then gets washed away, so the coastline is retreating

About 1.8m of land is lost to the sea every year, in some places e.g. Great Cowden the rate of erosion is over 10m per year

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Case Study, Holderness- main reasons

  • easily eroded rock type-
    • the cliffs are mainly made of boulder clay which is easily eroded. Its likely to slump when its wet, causing the cliffs to collapse
  • naturally narrow beaches-
    • beaches slow waves down, reducing their erosive power so narrow beaches give less protection
  • people worsening the situations-
    • coastal defences called groynes have been built at Mappleton. Groynes stop material from being moved further down the coast. This means the beaches are narrower and more easily eroded in some places
  • Powerful waves-
    • holderness faces prevailing wind direction, which brings waves from the north east (from the Arctic Ocean) waves increase in power over this long distance, so the coast is battered by highly erosive waves
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Case Study, Holderness- Impacts

On people:

  • Homes near the cliffs (e.g. in Skipsea) are at risk collapsing into the sea
  • Property prices along the coast have fallen sharply for those houses at risk from erosion
  • Accessibility to some settlements have been affected because roads near the cliff tops are at risk of collapsing into the sea e.g. Southfield Lane which runs between Skipsea and Ulrome has been closed
  • Businesses are at risk from erosion so people will lose their jobs e.g. Seaside caravan park at Ulrome is losing an average of 10 pitches a year
  • The gas terminal in Easington is at risk as its only 25m from the cliff edge, it counts for 25% of Britain's gas supply 

Environmental:

  • some SSSI's (sites of special scientific interest) are threatened e.g. the Lagoons near Easingston are part of and SSSI, the lagoons are separated from the sea by a narrow bar, if this is eroded the lagoons would be destroyed
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Coastal Management Schemes

Hard engineering- man made structures built to control the flow of the sea and reduce flooding and erosion

Soft engineering- schemes set up using knowledge of the sea and its processes to reduce the effects of flooding and erosion

Sea Wall (h)

  • A wall made out of hard material like concrete that reflects waves back into sea
  • It prevents erosion of the coast and acts as a barrier to prevent flooding
  • it creates strong backwash which erodes under the wall
  • expensive to build and maintain

Rock armour (h)

  • Boulders that are piled up along the coast
  • absorb wave energy so reduce erosion and flooding, fairly cheap
  • can be moved around be strong waves so need to be replaced
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Coastal Management Schemes

Groynes (h)

  • wooden or stone fences that are built at right angles to the coast, they trap material transported by longshore drift
  • create wider beaches which slow the waves, this gives greater protection from flooding and erosion, fairly cheap
  • starve beaches further down the coast of sand making them narrower
  • narrower beaches don't protect the coast as well leading to greater erosion

Beach Nourishment (s)

  • sand and shingle from elsewhere added to the beach
  • creates wider beaches which slow waves giving better protection
  • taking material from seabed can kill organisms like sponges and coral
  • its very expensive and has to be repeated
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Coastal Management Schemes

Dune regeneration (s):

  • creating or restoring sand dunes by nourishment or planting vegetation to stabilise the sand
  • provide a better barrier between land and sea as wave energy is absorbed preventing flooding and erosion, stabilisation is cheap
  • the protection is limited to a small area, nourishment can be expensive

Marsh creation (s):

  • planting vegetation in mudflats- stabilises the mudflats helping reduce speed of waves, also creates new habitats
  • isn't useful where erosion rates are high because can't become established
  • its expensive
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Coastal Management Schemes

Managed retreat (s) :

  • Removing an existing defence and allowing land behind to flood
  • over time the land will become marshland creating new habitats
  • flooding and erosion are reduced behind the marshland
  • its fairly cheap
  • people may disagree over what land is allowed to flood e.g. flooding farmland would affect livelihoods of farmers
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Case Study, Coastal Management- Holderness

11.4km of the Holderness coastline has been protected by hard engineering

  • Birlington is protected from erosion and flooding by a 4.7km long sea wall as well as wooden groynes
  • Hornsea- there is a sea wall, wooden groynes and rock armour to protect the village from erosion and flooding
  • Withernsea- groynes to create wider beaches, and a sea wall, some rock armour was placed in front of the wall after it was damaged in severe storms in 1992
  • Mappleton- two rock groynes were built in 1991 and cost £2million and were to protect the village and coastal erosion
  • eastern side of Spurn Head- protected by groynes and rock armour also protects the Humber estuary behind Spurn Head
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Case Study, Coastal Management- Holderness, proble

  • groynes protect local area but cause narrow beaches to form further down the Holderness coast which increases erosion down the coast e.g. Cowden Farm is now at risk of falling into the sea
  • The material produced from the erosion of Holderness is normally transported south into the Humber Estuary and down the Lincolnshire coast, reducing the amount of material that's eroded and transported south increases the risk of flooding in the Humber estuary because there is less material to slow floodwater down
  • the rate of coastal retreat along the Lincolnshire coast has increase because less new material is being added
  • Spurn head is at risk of being eroded away because less material is being added to it
  • Bays are forming between the protected areas, and the protected areas and becoming headlands which are being eroded more heavily, means maintaining the defences in the protected areas is becoming more expensive
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Case Study, Coastal Habitat- Studland Bay

Studland bay us a coastal area with beaches, dunes and heathland

Studland bay is in Dorset in the South West of England

It is mostly sheltered from highly erosive waves but the southern end is being eroded

there are sandy beaches around the bay with sand dunes and heathland behind them

The heathland is a Site of Special Scientific Interest (SSSI) and a nature reserve

its also a popular tourist destination

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Case Study, Studland Bay, Wildlife

wildlife found in Studland bay:

  • Reptiles like adders, grass snakes, sand lizards and slow worms
  • Birds like Dartford warblers, shelducks and grebes
  • fish like seahorses- only place in Britain where the spiny seahorse breeds
  • Plants like marram grass and lyme gress on the sand dunes and heather in the heathland

some organisms are specially adapted to the habitats found in Studland Bay

  • marram grass has folded leaves to reduce water loss- sand dunes are dry and windy which increases transpiration, have long roots to take up water and stabilise itself in the sand
  • Lyme grass has waxy leaves to reduce water loss by transpiration
  • grebes are birds which dive underwater for food, their feet are far back on their bodies
  • snakes and lizards have thick, scaly skin to reduce water loss from their bodies, also protects them from rough undergrowth on the heathland
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Case Study, Coastal Habitat- Studland Bay, conflic

some human activities e.g. recreation don't use the environment in a sustainable way, the environment is managed to make sure its conserved but can be used for:

lots of people walk across sand dunes has caused lots of erosion, the National Trust manages the area so people can use the sand dunes without being too damaging:

  • boardwalks are used to guide people over the dunes and protect sand beneath
  • some have been fenced off and marram grass planted to recover and stabilise
  • information signs put up to let visitors know about the importance of sand dunes

Hundreds of boats use Studland bay and their anchors are destroying sea-grass where seahorses live, they are protected by law so boat owners are told not to damage grass

The heathland behind the sand dunes is an important habitat but it can be damaged by fires caused by things like cigarettes e.g. in 2008 a fire destroyed 6 acres of heathland, the national trust is educating visitors on the dangers of causing fires and has provided fire beaters

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Comments

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I used to be smart

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