Rock is broken down by mechanical+chemical weather
Mechanical weathering- the breakdown of rock without changing its chemical composition.
- It happens when the temperature alternates above and below 0 degrees (the freezing point of water).
- Water gets into rock that has cracks, e.g. Granite.
- When the water freezes it expands, which puts pressure on the rock.
- When the water thaws it contracts, which releases the pressure on the rock.
- Repeated freezing and thawing widens the cracks and causes the rock to break up.
Chemical weathering- the breakdown of rock by changing its chemical composition.
- Rainwater has carbon dioxide dissolved into it, which makes it a weak carbonic acid.
- Carbonic acid reacts with rock that contains calcium carbonate, so the rocks are dissolved by the rainwater.
Mass movement is the shifting of rocks and loose material down a slope, e.g. a clif.
Mass movements cause coasts to retreat rapidly.
They're more likely to happen when the material is full of water; the water acts as a lubricant.
You need to know about 2 types of mass movement:
Slides- when material shifts in a straight line
Slumps- when material shifts with a rotation.
Waves Wear Away Coasts Using 4 Processes Of Erosio
1) hydraulic power- waves crash agaist rock and compress the air in the cracks. This puts pressure on the rock. Repeated compression widens the cracks and makes bits of rock break off.
2) Abrasion- eroded particles in the water scrape and rub against rock, removing small pieces.
3) Attrition- Eroded particles in the water smash into ech other and break into smaller fragments. Their edges also get rounded off as the rub together.
4) Soultion- weak carbonic acid in seawater dissolves rock like chalk and limestone.
The waves that carry out erosional processes are called destructive waves;
- Destructive waves have a high frequency (10-14 waves per minute)
- They're high and steep
- Their backwash (the movement of water back down the beach) is more powerful than thier swash (the movement of water up the beach). This means material is removed from the coast.
Waves erode cliffs to form wave-cut platforms
1) Waves cause most erosion at the foot of the cliff
2) This forms a wave-cut notch
3) The rock above the notch becomes unstable and eventually collapses.
4) The collapsed material is washed away and a new wave-cut notch starts to form.
5) Repeated collapsing results in the cliff retreating.
6) A wave-cut platform is the platfrom that's left behind as the cliff retreats.
Headlands And Bays- Erosion Resistance
- Some types of rock are more resistant to erosion than others.
- Headlands and Bays form where there are alternating bands of resistance 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 more slowly and it's left jutting out, forming a headland- headlands have steep sides.
Headlands Are Eroded To Form Caves, Arches and Sta
Headlands are usually made of resistant rocks that usually have weaknesses like cracks.
Waves crash into the headlands and enlarge the cracks- mainly by hydroaulic power and abrasion.
Repeated erosion and enlargement of cracks causes a cave to form.
Continued erosion deepens the cave until it breakes through the headland- foriming an arch, e.g. Durdle Door in Dorset.
Erosion continues to ware away the rock supproting the arch, until it eventually collapses.
This forms a stack- an isolated rock that's seperate from the headland, e.g. Old Harry in Dorset.
Waves follow the direction of the pravailing wind.
- They usually hit the coast at an oblique angle (and angle that isnt a right angle.
- The swash carries material up the beach, in the same direction as the waves.
- The backwash then carries material down the beach at right angles, back towards the sea.
- Over time, material zigzags along the coast.
There are 4 other processes of transportation;
Traction- large particles like boulders are pushed along the sea bed by the force of water.
Suspenion- small particles like silt and clay are carried aling in the water.
Saltration- pebble-sized particles are bounced along the sea bed by the force of water.
Solution- soluble materials dissolve in the water and are carried along.
Longshore Drift Diagram
Deposition is the dropping of material.
Deposition is when material being carried by the sea wter 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 everywhere on the coast, so there's lots of material available.
- There's lots of transportation of material into the sea.
Low energy waves (slow waves) carry material to the coast but aren't strong enough to take a lot of material away- this means there's lots of deposition and very little erosion.
Waves that deposit more material than they erode are called constructive waves:
- Constructive waves have a low frequency (6-8 waves per minute)
- They're 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. This means material is deposited on the coast.
Beaches are formed by deposition.
1) beaches are found on coasts between the high water mark (the highest point on the land that the sea level gets to)
2)They're formed by constuctive waves depositing materials like sand and shingle.
3) Sand and shingle beaches have different characteristics:
Sand beaches are flat and wide- sand particles are small and the weak backwash can move them back down the beach, creating a long gentle slope.
Shingle beaches are steep and narrow- shingle particles are large and the weak backwash can't move them back down the beach. The shingle particles build up and create a steep slope.
Spits are basically just beaches that stick out into the sea- they're joined to the coast at one end. If a spit sticks out so far that it connects with another bit of the mainland, it'll form a bar. Spits and bars are formed by longshore drift.
- Spits form at sharp bends in the coastine, e.g. a 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 (forming a recurved end)
- The sheltered area behind the spit is protected from waves- lots of material accumalates in this area, which means plants can grow there.
- Over time, the sheltered area can become a mud flat or a salt marsh.
A bar is formed when a spit joins two headlands together, e.g. there's a bar at Slapton in Devon.
The bar cuts off the bay between the headlands from the sea.
This means a lagoon can form behind the bar.
Coastal Flooding- Case Study, Social, environmenta
The Maldives is a group of islands in the Indian ocean.
- Population: about 300,000 people
- Number of islands: 1190, of whcih 199 are inhabited
- Average island height: 1.5m above sea level- 80% of the land is below 1m. Within 50-100 years scientists believe the islands will be completley submerged due to rising sea levels.
Coastal flooding has a variety of impacts on the Maldives;
- Social- Houses damaged or destroyed- a severe flood could make entire communities homeless.
- Less freshwater available- supplies of fresh water 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- costal flooding wears away beaches on the islands at a rapid rate. This destroys habitats and exposes the land behind the beach to the effects of flooding.
- Loss of soil- the soil on most of the islands is shallow (about 20cm deep or less). Costal floods could easily wash away the soil layer, which would mean most plants won't be able to grow.
Coastal Flooding- Case Study, Economic, political
Loss of tourism-
- toruism is the largest industry in the Maldives. If the main airport can't work properly because of coastal flooding the country will be cut from international tourists. The will massively reduce the country's income.
- Disrupted fishing industry- fish are the Maldives largest export. Coastal flooding may damage fish processing plants, reducing the fish exports and the country's income.
- The Maldivian government had to ask the Japanese government to give them $60 million to rebuild the 3m high sea wall that protects the capital city, Male.
- Changes to environmental policies- increased flooding is caused by rising sea level, whci is caused by global warming. The Maldives have pledged to become carbon neutral so it doesn't contribute to global waarming. The Maldivian government is 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 andmoving Maldivians there, before the islands become inhabitable.
Coastal erosion- Case Study
The average rate of erosion at Holderness is about 1.8 metres per year.
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 has been over 10m per year in recent years.
Coastal Erosion- Case Study- Reasons for RE
Main reasons for rapid erosion:
Easily eroded rock type- the cliffs are mostly made of boulder clay which is easily eroded. It's likely to slump when it's 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 situation- 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 other places.
Powerful waves- Holderness faces the prevailing wind direction, whcih brings waves from the north east (all the way from the Artic ocean). Waves increase in power over this long distance, so the coast is battered by hihgly erosive waves.
Coastal erosion- Case study- Impact on lives
Impacts on people's lives:
- 1)Homes near the cliffs are at risk of collapsing into the sea.
- 2)Property prices along the coast have fallen sharply for those hpuses at risk from erosion.
- 3) Accesibility to some settlements has 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.
- 4) 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.
- 5) The gas terminal at Easington is at risk (it's only 25m from the cliff edge). This terminal accounts for 25% of Britain's gas supply .
- 6) 80,000m squared of farmland is lost each year. This has a huge effect on farmer's livelihoods.
Some sites of special scientific interest are threatened- e.g. the lagoons near Easington are part of the SSSI. The lagoons are seperated from the sea by a narrow strip of sand and shingle ( a bar). If this is eroded it will connect the lagoons to the sea and they would be destroyed.
Coastal management strategies- Hard engineering
Hard engineering- man made structures built to control the flow of the sea and reduce flooding and erosion.
- What is it? A wall made out of a hard material like concrete that reflects waves back to the sea.
- Benefits- prevents erosion of the coast -Also acts as a barrier to prevent flooding.
- Disadvantages- it creates a strong backwash, which erodes under the wall -Sea walls are very expensive to build and maintain.
- What is it? boulders that are piled up along the coast.
- Benefits- the boulders absorb wave energy and so reduce erosion and flooding - fairly cheap
- Disadvantages- boulders can be moved around by strong waves so they need to be replaced.
Hard engineering continued
What are they? wooden or stone fences that are built at right angles to the coast. They trap material transported by longshore drift.
- Groynes create wider beaches which slow the waves. This gives greater protection from flooding and erosion.
- They're a fairly cheap defence.
They starve beaches further down the coast of sand, making them narrower. Narrower beaches don't protect the coast as well, leading to greater erosion and floods.
Soft engineering ( Beach nourishment+Dune regenera
Beach nourishment,, What is it? - sand and shingle from elsewhere (e.g. the offshore seabed) is added to beaches.
Benefits- beach nourishment creates wider beaches which slow the waves. This gives greater protection from flooding and erosion.
- taking material from the seabed can kill organisms likes sponges and corals.
- It's a ver expensive defence.
- It has to be repeated
- Dune regeneration,, What is it? - creating or restoring sand dunes by either noruishment, or by planting vegetation to stabilise the sand.
- Benefts- sand dunes provide a barrier between the land and the sea. Wave energy is absorbed which prevents flodding and erosion.
- Stabilisation is cheap.
Disadvantages?- the protection is limited to a small area, Nourishment is very expensive.
Soft engineering (Marsh creation+ Managed retreat)
Marsh creation,, What is it? - Planting vegetation in mudflats along the coast.
- Benefits- The vegetation stabilises the mudflats and helps to reduce the speed of the waves. This prevents flooding and erosion.
- It also creates new habitats for organisms.
- Disadvantages? - Marsh creation isn't useful where erosion rates are high because the marsh can't establish itself.
- Its a fairly expensive defennce.
Managed retreat,, What is it? - removing an existing defence and allowing the land behind it to flood.
- Benefits?- Overtime the land will become marshland- creating new habitats. Flooding and erosion are reduced behind the marshland.
- It's a fairly cheap defence.
Disadvantages- People may disagree with what land is allowed to flood, e.g. flooding farmland would affect the livlihood of farmers.
Hard engineering pictures
Coastal management- Case study- Holderness
Hard engineering stratagies that have been used along Holdnerness
Bridlington is protected from erosion and flooding by a 4.7km long sea wall as well as wooden groynes.
There's a sea wall, ooden groynes and rock armour at Hornsea that protect the village from erosion and flooding.
There are groynes to create wider beaches and a sea wall at Whithernsea. Some rock armour was placed in front of the wall after it was damaged in severe storms in 1992.
Defences including 2 rock groynes, were built at Mappleton in 1991. They cost £2 million and were built to protect the village and a coastal road from erosion and flooding.
The Eastern side of Spurn Head is protected by groynes and rock armour. This also protects the Humbler Estuary behind Spurn Head.
Holderness- Problems elsewhere..
The strategies are locally successful butcause problems elsewhere;
1) Groynes protect local areas but cause narrow beaches to form further down the Holdnerness coast. This increases erosion down the coast, e.g. Cowden farm (south of Mappleton) is now at risk of falling into the sea.
2) The material produced from the erosion of Holderness is normallytransported south into the Humber estuary and down the Lincolnshire coast. Reducing the amount of material that's eroded and transported south incraeses the risk of flooding in the Humber estuary, because there's less material to slow the floodwater down.
3) the rate of coastal retreat along the Lincolnshire coast is also inccreased, because less new material is being added.
4) Spurn Head is at risk of being eroded away because less material is being added to it.
5) Bays are forming between the protected areas, and the protected areas are becoming headlands which are being eroded more heavily. This means maintaining the defences in the protected areas is becoming more expensive.
Coastal habitat- Case study- Stutland bay
Stutland bay is a coastal area with Beaches, Dunes and Heathland.
1) Stutland bay is a bay in Dorset, in the South West of England.
2) It's mostly sheltered from highly erosive waves, but the southern end of the bay is being eroded.
3) There are sandy beaches around the bay, with sand dunes and heathland behind them.
4)The heathland is a site of special scientific interest (SSSI) and a nature reserve.
5) Stutland bay is also a popular tourist destination.
Hard engineering pictures
Examples of wildlife found in Stutland Bay:
- Reptiles like adders, grass snakes, sand lizards and slow worms.
- Birds like Dartfrod warblers (a rare bird in England), shelducks and grebes
- Fish like seahorses- Stutland Bay is the only place in Britain where the spiny seahorse breeds.
- Plants like marram grass and lyme grass on the sand dunes and heather on the heathland.
Some of these organisms are specifically adapted to live in the habitats found in Stutland Bay;
- 1) Marram grass has folded leaves to reduce water loss- Sand dunes are windy and dry which increases transpiration. It also has long roots to take up water and to stabilise itself in the loose sand.
- 2) Lyme grass has waxy leaves to reduce water loss by transpiartion.
- 3) Grebes- these birds dive underwater to find food in the sea. Their feet are far back on their bodies to help them dive (it makes them streamlined).
- 4) Snakes and lizards have thick, scaly skin to reduce water loss from their bodies. It also protects from the rough undergrowth on the heathlands.
Studland Bay continues.......
There are conflicts between land use and the need for conservation; some human activities (e.g. recreation) don't use the environment in a sustainable way (they use up resources or damage the environment). The environment is managed to make sure it's conserved, but can also be used for other activities:
1) Lots of people walk across the sand dunes which has caused aa lot of erosion. The national trust manages the area so people can use the sand dunes without damaging them too much:
- Boardwalks are used to guide people over the dunes so the sand beneath them is protected.
- Some sand dunes have been fenced off and marram grass has been planted in them. This gives the dunes a chance to recover and the marram grass stabilises the land.
- Information signs have been put up to let visitors know why the sand dune habittat is important, and how they can enjoy the environment without damaging it.
2) Hundreds of boats use Stutland Bay and their anchors are destroying the seagrass where seahorses live. Seahorses are protected by law, so boat owners are being told not to damage the seagrass.
3) The heathland behind the sand dunes is an important habitat, but it can be damaged by fires by things like cigarettes- the national turst is educating visitors about these dangers.