- Created by: nataly
- Created on: 20-05-11 17:45
Processes of Erosion
Waves crash against rock and compresses air into the cracks, putting pressure on the rock and the rock eventually cracks.
Eroded particles in the water scrape and rub against rock, removing small pieces.
Eroded particles in the water smash into each other and break into smaller fragments and are smooth and rounded.
Weak carbonic acid in the sea water dissolves rock such as chalk and limestone.
Processes of Transportation
Large boulders are pushed along the sea bed by the force of the water.
Pebble sized particles are bounced along the sea bed by the force of the water.
Small particles like silt and clay are carried along in the water.
Soluble materials dissolve in the water and are carried along by the sea.
Occurs when temperatures alternate above and below 0°C , and water gets into a rock with cracks e.g. Granite. When the water freezes the rock expands by 9% which puts pressure on the rock. When the water thaws it contracts and the pressure on the rock is released. Repeated freezing and thawing widens the crack and causes the rock to break up.
When the coastline comes in contact with acid from the rain and salt from the seawater it creates carbonic acid which then causes the rock to react with it results in rocks breaking down.
Headlands & Bays
vSome types of rocks are more resistant to erosion than others.
vHeadlands and bays form where there are alternating bands of resistant and less resistant rock along the coast.
vThe less resistant rock (e.g. Clay) is eroded quickly and this forms a bay.
vThe resistant rock (e.g. Chalk) is eroded slower and is left jutting out forming a headland.
Caves, Arches, Stacks and Stumps
- a soft part of a rock cracks and gets eroded by Hydraulic power. This carried on until the cave gets bigger, but doesn't go all the wat through.
- an arch is where a cave has been eroded all the way through on a headland.
- the top of an arch has fallen down after years of erosion as it can't be supported any more.
- a stack has been eroded so much that in shrinks in size becoming a Stump.
- The process of moving sediment down the beach
- Prevailing winds mean the Swash carries sediment up the beach.
- The Backwash carries the sediment back down the beach.
- The waves are at an angle when they approach the beach.
- It doesn't happen at all beaches because most waves come straight on.
A Spit and A Bar
- Longshore Drift carries material along the coastline due to prevailing winds.
- When there is a change in direction, sediments continue to be deposited by Longshore Drift.
- Prevailing winds cause the end of the spit to curve.
- Large storms can destroy or reduce the length of the spit.
- The spit shelters the sea behind it. Overtime, the sheltered area can become a mudflat or a salt marsh.
- A bar is formed when two headlands join together. A Bar cuts off the bay between the headlands from the sea.
Mass movement is the shifting of rocks and loose material down slope. It happens when the force of gravity acting on a slope is greater than the force supporting it.
•Material shifts in a straight line
•Material shifts with a rotation
Case Study information – Coastal Erosion at Holder
The Holderness coastline is 61km long.
It stretches from flamborough head to spurn head.
Erosion is causing the cliffs to collapse along the coastline, and as the material is washing away, the cliff is constantly retreating.
About 1.8m of land is lost every year and in some places (e.g. Great Cowden), the rate of erosion is over 10m per year.
Case Study: Holderness coast erosion
vThere are 4 main reasons why the Holderness coast is eroding so quickly;
vEasily eroded rock type- The cliffs on the Holderness coast are mainly made of boulder clay which is easily eroded. It’s likely to slump when wet, causing the cliffs to collapse.
vNaturally narrow beaches- Beaches slow down waves, reducing their erosive power and acting as a barrier. Narrow beaches give less protection towards the coast.
vPeople- Coastal defences called Groynes have been built at Mappleton. Groynes stop Longshore drift occurring which prevents any beach being built up further down the coast which means the beaches are even narrower.
vPowerful waves- Holderness faces prevailing wind direction which brings waves from the north east. These waves are powerful as they have a large fetch which means the coast is faced with highly erosive waves.
Case Study: Holderness coast erosion impacts
Impacts on people:
vHomes near cliffs are at risk of collapsing into the sea which means insurance is literally impossible to get. vProperty prices have fallen
vThe gas terminal in Easington is at risk as it’s only 25m from the cliff and it counts for 25% of Britain gas supply.
vAccessibily to settlements have been affected along the coast as roads have collapsed into the sea.
Impacts on environment:
vSome sites of special scientific interest (SSSI’S) have been threatened e.g. Lagoons near Easington. The lagoons are seperated from the sea by a narrow bar however if the bar is eroded the lagoons will be destroyed.
Hard and Soft Engineering
- Artifical structures are used to control natural processes.
- E.g. Sea Walls, Rock Armour or Groynes
- A sustainable approach, which uses natural techniques, is used to control natural processes.
- E.g. Beach nourishment, Dune regeneration, Mananged Retreat
Advantages & Dis-advantages:
Sea wall: A wall made out of hard material that reflects waves back out to sea. It prevents erosion on the coast and acts like a barrier. On the other hand it creates a strong backwash which erodes under the wall and is very expensive to build and maintain.
Rock Armour: Rock armour are large boulders that are built up along the coast. The boulders absorb the wave energy they reduce the risk of erosion against the coast. They are fairly cheap however they can be moved around by strong waves so they need to be replaced frequently.
Groynes: Groynes are wooden or stone fences that are built at right angles to the coast. They trap material transported by longshore drift. They create wider beaches which slow the waves down and give bigger protection along the coast. On the other hand beaches further down the coast suffer as there is no beach being deposited. This means the beaches are narrower and more prone to erosion.
Advantages & Dis-advantages:
Beach Nourishment. Beach nourishment is sand and shingles that are added to the beach from out to sea. It creates wider beaches which slow waves down and protect the coast from further erosion. On the other hand taking material from the seabed can kill habitats and is very expensive and has to be managed frequently.
Managed Retread: Managaed retreat is removing an existing defence and allowing the land behind to flood. Over time the land will become marshland and new habitats will occur. Also erosion is reduced behind the marshland and it’s cheap. However, people disagree over what land is allowed to flood as flooding farmland would affect farmers.
Sand Dunes: Creating dunes by nourishment or plating vegetation provides a better barrier between land and sea as wave energy is absorbed preventing erosion. Also stabalisation is cheap. On the other hand the protection area is limited and nourishment can be expensive.
Marsh Creation: Planting vegetation in mudflats reduce speed of waves and creates new habitats. However it’s expensive and it isn’t useful where erosion rates are high.
Causes of sea level rise
The melting ice on the land (e.g. The Antarctic ice sheet) causes water that’s stored as ice to return to the ocean when the ice is melted.
This means the volume of the water increases and sea levels rise.
Global warming causes the sea levels to rise as greenhouse gases are released into the atmosphere, warming the earth which causes the sea leavel to rise.
Increased global temperatures cause the oceans to get warmer and when water is heated it expands. This increases the volume of the water and causes sea levels to rise.
Economic Impacts on the Maldives
vLoss of tourism: Tourism is the largest industry in the Maldives and if the main airport can’t work properly because of flooding the country will be cut off from international tourists. This will massively reduce the country’s income.
vDisrupted fishing industry: Fish are the Maldives largest export. Flooding may damage fish processing plants, which will reduce fishing exports and eventually the country’s income.
Social impacts on the Maldives
vHouses are damaged or destroyed: Severe floods can leave entire communities homeless.
vLess freshwater available: Supplies of freshwater are already low on many of the island. 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 impacts on the Maldives
vLoss of beaches: Coastal flooding wears away beaches on the islands at a rapid rate. This destroys habitats and exposes lands behind the beach to effects of flooding.
vLoss of soil: The soil on most of the islands is shallow (about 20cm deep or less). Coastal floods couldn't easily wash away the soil layer which would mean most plant’s wont be able to grow.
Political Impacts on the Maldives
vThe Maldivian Government had to ask the Japanese Government to give them $60 million to build a 3m high sea wall that protects the city, Malé.
vChanges to environmental polices: Increased flooding is caused by rising sea levels which is caused by global warming. The Maldives have pledged to become carbon neutral so it doesn’t contribute to global warming. They are encouraging other governments to do the same.
vChanges 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.
Impacts of Coastal Erosion
- A wave-cut notch occurs because of erosion then the cliff becomes unstable and collapses.
Impacts Of Coastal Erosion
- Loss of houses
- Loss of habitat for wildlife
- Job losses
- No house insurance
- Loss of tourism and money
Salt Marsh Case Study - Keyhaven Marshes
- The beach is retreating up to 6m per year.
- The marsh is eroding which exposes the beach.
- More tourism is causing pollution and damage to the Marshes.
- Sea levels are rising and the low sea wall is under threat.
- The Ringed Plover feeds and nests on the salt marsh.
- The Wold Spider clings to Cordgrass waiting for food.
- The Sea Lavender attracts Wildlife and is pretty.
- Rock Armour and beach Nourishment was introduced in 1996, and the spit has not been breached.
- The marsh is now a SSSI so access is limited and the area is being watched.
What are salt marshes?
- They are places where the sea has flooded the land between high and low tide and example of one would be key haven marshes which is located behind Hurst castle spit