The sea erodes the coast in four ways:
* Hydraulic Action
Lots of sea and water crashes against the land, and air and water are trapped and compressed in rock surface cracks. When the sea moves again the air expands explosivel weakening the rocks, enlarging the cracks and breaking pieces off.
* Corrasion (abrasion)
This is very effective and is caused by brocken rock fragments hitting the land, cliffs etc.. and breaking off other pieces of rocks.
This occurs when rock fragments grind against each other down into smaller and smoother pebbles and shingle and finally sand which is later deposited as beaches etc…
This involves chemical action of sea on rock. If the rock is limestone, it dissolves in the sea water – some salts can also react with certain rocks and cause them to rot.
Swanage Bay is made up of a less dense rock called clay. For this feature it is wealden clay. Swanage Bay can be found between 043,787 and 047,812 on the map. This type of rock is non-permeable therefore it is easily eroded. Wave refraction, deposition and corrosion forms bays. Deposition is when sediments such and sand and shingle are washes onto the shore.
If there are alternate bands of hard and softer rocks in the coastline, the harder rocks will take longer to erode than the softer rocks because the sea has less effect on the harder rocks. The hard rock will be left sticking out forming headlands usually with cliffs. The softer rocks will be eroded to form bays. The erosion causes the bays usually to slope move gently inland, creating room for a beach to form. Beaches then do not stay in one position. The crashing of the waves causes the sand and shingle to move along the coast and gather at a single point, this process is known as longshore drift.
A longshore drift is the movement of beach sediments along the shore. A longshore drift occurs where waves transport material along the beach if dominant waves approach the beach at an angle. The swash carries the material along the beach. However, the back wash will carry the material back down. This orocess will be repeated throughout the whole of the beach. In order to slow this process, groynes are built. The purpose of groynes are to keep the beach material in one place, as the material slows down further erosion of the bay.
Longshore drift also causes spits to form, which are long, narror paths with one end attached to land and the other projecting at a norrow angle in the sea often with a hooked or curved end.
Spits are formed when sand and shingle are carried by longshore drift. In the shelter of the bay or at the bend in the coastline, depostion of sand and shingle occurs. The sand and shingle are deposited over time by longshore drift which then build up with time to form a long ridge.
I think in the future the erosion will not change from the present day. I would say that the two headlands, Ballard Point and Peveril Point are likely to remain as they are. Wave cut platforms may differ the headland forming the caves at their bases. The main Swanage Bay are may constantly be retreating and the coast may deepen. This process may not be stopped but new groynes built might help slow down the process.
There are three main features found in The Foreland:
* Natural Arch
The Natural Arch can be found at 056,824. They are formed from caves and develop at opposite sides of the headland to join up. It is also caused by destructive waves. Arches are made from resistant permeable rock and are tall and vertical. As waves continue to erode the base of the arch, its roof becomes too heavy to be supported and collapses leaving part of the cliff isolated.
Old Harry (found at 058,827), and Old Harry’s Wife (found at 058,826), were both stacks but now Old Harry’s Wife is a stump. They are both near the Natural Arch. A stack is a steep sided rocky heap located offshore from coastal cliffs and natural arches. They are formed from resistant permeable rock and formed when the rock above the arch became too heavy to be supported and so collapsed. Old Harry can be said to be like a ‘tall pillar’. The geometric processes which have formed this feature are corrasion, destructive waves and hydraulic action. These processes will carry on colliding against the stack (Old Harry), until eventually the stack collapses leaving a stump (Old Harry’s Wife)
* Wave-Cut Platforms
There could be a wave-cut platform forming at The Foreland at 056,826. Waves erode rocks along the shore line by hydraulic action, corrosion and corrasion. A notch is slowly formed at the high water mark which may develop into a cave. Rock above the notch becomes unstable with nothing to support it and so collapses. The coastline retreats over many years as this process continues to form a wave-cut platform. The actual size and angle of the cliff will depend on the local rock and its hardness.
In the United Kingdom, coastal erosion is becoming more common. Coastal erosion is carried on naturally in remote areas, but there are social and economic reasons to stop or slow down the coastal processes in inhabited areas.
North Norfolk coast is located between Overstrand and Mundesley which is on the north eastern coast of Norfolk bordered by the North Sea (eastern England).
There have been three major incidents which have occurred due to the action of the waves colliding against the cliffs:
1. The first major cliff collapse occurred in 1989 in Sidestrand on grid reference 261,402 close to the local resident’s small holding. It occurred because there was no planning permission in that area which meant the cliff could not be protected and stopped from collapsing. It has been noticed that cliff collapse it common in this area. The problems seem to be worse at the eastern part of this area, but the affect on the area is increasing.
2. Another major cliff collapse then took place in 1990 in Trimingham on grid reference 283,388. There was also no planning permission in that area. The cliff collapsed as a result to slumping of the cliff and so revetment was involved. The problem with revetment is the level of the shingle changes during the year causing the exposed base of the cliff to be under cut by winnter high tides and gales. This then causes the cliff to collapse.
3. The last major cliff collapse took place over a three year period between 1992-94 in Overstrand on grid reference 254,406. This incident destroyed roads and houses. This event was one which the local authorities were not prepared for such an event. The cliff was retreating at a fast rate up until this time at approximately three meters every year. But all of a sudden 45 meters collapsed in one go. This is shows how fast the process takes place and so the process must be monitored on a constant basis so nothing unexpected will take place again. Therefore if the loss of land of planning to be stopped then sea defences are an important factor to consider. It is likely that the same problem with the cliff is going to take place again in that area of the Norfolk coastline in the future.
The Main Reasons for Coastal Erosion
The four main reasons for coastal erosion are geology, weathering, the sea and human activity.
The geology of coast erosion has something to do with the type of rock the cliffs are made of. In North Norfolk the cliffs are made of soft rock, boulder clay. This clay is very easily eroded.
During an ice age the weight of the ice sheet pushes that continent into the Earth’s mantle; once the ice has melted, the continent rises again. This accounts for shoreline features being found some way inland in regions that were heavily glaciated during the Pleistocene period.
Weathering is also involved with the erosion of the coast. With the help of rainfall slumping occurs.
Slumping is when soft rock which lies above hard rock gets water logged and falls down the cliff into the sea.
Freeze-thaw also helps with the process of coastal erosion. Freeze-thaw is the splitting of rocks by the alternate freezing and thawing of water trapped in cracks. Exfoliation, or onion-skin weathering, the flaking caused by the alternate expansion and contraction of rocks in response to extreme changes in temperature may also affect coastal erosion.
The sea is also a major part of the erosion and corrosion of the coast. A constructive wave causes a net deposition of material on the shore because its swash is stronger than its backwash. Such waves tend be low and have crests that spill over gradually as they break. A destructive wave is stronger than its swash, and therefore causes a net removal of material from the shore. Destructive waves are usually tall and have peaked crests that plunge downwards as they break, trapping air as they do so. The swash is when the water pushes materials up the beach as incoming waves break, and the backwash is the return of water back down the beach (always at a right-angle).
The fetch for North Norfolk comes from Norway which is 550 miles away. This means that the fetch is not all that strong. The fetch is the distance of open water over which wind can blow to create waves. The greater the fetch the more potential power waves have when they hit the coast.
The gravitational pull of the Moon is the main cause of the tides. Water on the side of the Earth nearest the Moon feels the Moon’s pull and accumulates directly under the Moon. When the Sun and the Moon are in line, at new and full moon, the gravitational pull of Sun and Moon are in line and produce a high spring tide. When the Sun and Moon are at right angles, lower neap tides occur.
When there are high tides there is a much more likely chance of coastal erosion. While the tide is moving up and down the erosion of the coast is higher.
Long shore Drift also affects erosion and corrosion of the coast. Long shore Drift is the movement of material along the beach. When a wave breaks obliquely, pebbles are carried up the beach in the direction of the wave. The wave draws back at right angles to the beach, caring some pebbles with it. In this way, material moves in a zigzag fashion along a beach. Long shore Drift is responsible for the erosion of beaches and the formation of spits (ridges of sand or shingle projecting into the water). Attempts are often made to halt Long shore Drift by placing barriers, or groynes, at right angles to the shore.
Human activity is another major point to coastal erosion and corrosion. When roads and buildings are built onto the cliffs, they put weight on them causing them to collapse.
Global warming causes the glaciers in Antarctica to melt. This makes sea levels rise, which means the sea may flood villages and/or make erosion much easier.
If some towns build coastal defences there town is protected from Long shore Drift, but this means that further down the shore the Long shore Drift is made much stronger and smaller towns may end up being destroyed.
The Norfolk coast is made of clay, which is impermeable rock, so during heavy rains water will not soak into the ground, but instead will collect in channels in the ground to from underground streams. With this taking place the ground will become unstable and slippery. The face of the cliff is exposed to strong wave action which then removes the lower section of the cliff face. This process is known as corrasion. This leave the upper section of the cliff unsupported and so the unstable structure slides down into the sea, where it is then washed away by waves.
The upper section of the cliff is unstable and then by removing the weight of the upper section by forming a gentle slope will reduce the risk of cliff collapse as the upper part of the cliff above the base is more unstable.
The Effects of Costal Erosion on People
Local residents such as Miss Younger and Mr Singh want to build extensions but cannot get loans from the bank in order to do the work. This because they think the land would not be there for long. Some land nearby has already been sold and bought by a local builder who wanted to build new houses on the land but know cannot get planning permission. He has also been affected by Miss Younger and Mr Singh not building their extensions.
People such as Mr and Mrs Kinsley are also going to be affected even though their cottage is in the right side of the planning line. They have been living in the same cottage for the whole of their lives. Their main worry is that they may have to move away from their home, either because of cliff collapse or because the council want to evacuate the area for safety reasons.
The Hotel Belle Vue located in Mundesley is not at much risk as other properties in that area. In is further away from the coast where the cliffs are not too steep and are actually quite stable because of the grass and vegetation growing. The grass and vegetation play an important role in the effects. The roots allow the ground to keep stable and prevent water from soaking into the surface allowing it to run off without causing any problems. The main problem is that any work done to the cliff near Sidestrand will have an affect on their part of the land.
What might be done to slow down Coastal Erosion?
To slowly slow down coastal erosion and corrosion in North Norfolk many coastal defences are being built. These defences will stop Long shore Drift and receive all the energy from the harmful waves which are one of the main causes of this coastal erosion.
There are 4 main decisions which the government has to agree to do to certain parts of the North Norfolk coast. They could either:
* Manage the retreat – To plan to lose some of the land which is being eroded by the sea
* Hold the line – When coastal defences are built to try and stop some of the coastal erosion
* Advance the line – When the land is reclaimed. This option is not used in England but is used in Holland and other countries
* Do nothing – The coastal erosion is left to do what it does best
176 Colney Hatch Lane
13th June 2002
Norfolk County Council
Having completed my investigation on coastal erosion and cliff collapse in Norfolk along the Overstrand and Mundesley coastline, I have come up with possible options that can be used to improve the coastal areas of North Norfolk. I have taken into an account the local residents and businesses in my recommendations.
My points are:
* To increase drainage along cliffs with the use of drainage pipes and gravel drains.
* To use the armour blocks to protect the cliff bases to keep the local residents and businesses safe.
* To use groynes to reduce long shore drift to increase the amount of tourists.
* To slope cliff tops so that surface draining and vegetation can be encouraged.
These options will also help to slow down erosion therefore cause less problems to the local residents and businesses in the area.
Thanking you very much for taking time to read my suggestions and I hope you consider a few of my suggestions which I genuinely believe will be of enormous use.