Presentation on theme: "Coasts – The Essentials. How do land processes shape the coast? WEATHERING This is the disintegration and decay of rocks in their original place or close."— Presentation transcript:
Coasts – The Essentials
How do land processes shape the coast? WEATHERING This is the disintegration and decay of rocks in their original place or close to the ground surface, largely caused by the weather e.g. rainfall/temperature change. There are 3 main types: MECHANICAL/PHYSICAL – This is the disintegration of rock without any chemical changes taking place in the rock. This would result in piles of rock fragments (scree) accumulating at the base of a cliff. CHEMICAL – This involves a chemical change e.g. rainwater, which is slightly acidic, can slowly dissolve certain rocks. BIOLOGICAL – This involves the actions of animals (fauna) and plants (flora). Plant roots are very effective at growing and expanding in rock cracks. Animals such as rabbits and sea birds will burrow in weak raocks such as sandstone.
TYPES OF MECHANICAL/PHYSICAL WEATHERING FREEZE-THAW (frost shattering) EXFOLIATION (onion skin weathering) Exfoliation happens in areas which experience large changes in temperature. During the day when the rock heats up, it expands but at night when it cools, it contracts. When this is constantly repeated, the outer layer will often peel away from the rest of the rock.
TYPES OF CHEMICAL WEATHERING SOLUTION In the same way in which sugar dissolves in tea, some minerals and rocks dissolve in rainwater. This process is called solution. CARBONATION Carbonation is very similar to solution. It affects rocks that are made up of calcium carbonate e.g. chalk and limestone. Rainwater picks up carbon dioxide (CO2) in the air, so becomes a weak carbonic acid. This then reacts with calcium carbonate (found in rocks such as chalk/limestone) to form calcium bicarbonate which dissolves weak points in the rock, forming cracks (see photo on left)
MASS MOVEMENT Mass movement is the downhill movement of material under the influence of gravity. This will once again have an effect on the shape of a coastline. Common types of movement are: 1. Rockfall 2. Landslide 3. Mudflow 4. Rotational slip
Rockfall – fragments of rock break away from the cliff face, often due to freeze-thaw weathering, leaving screes at the base of the cliff Mudflow – where a layer of soil on top of a layer of rock becomes saturated (cannot soak up anymore water), it will flow down a slope.
Where layers of rock sit on one another at an angle, there is always the possibility that they will create a landslide, and slide downhill. A rotational slip is a slump of saturated soil and weak rock along a curved surface.
Destructive waves destroy beaches. The waves are usually very high and very frequent. The back wash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. These waves are most common in winter. Types of waves which shape the coastline
Constructive waves build beaches. Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer.
Attrition Material carried by the waves bump into each other and so are smoothed and broken down into smaller particles. Abrasion/Corrasion This is the process by which the coast is worn down by material carried by the waves. Waves throw these particles against the rock, sometimes at high velocity. Hydraulic action This process involves the force of water against the coast. The waves enter cracks (faults) in the coastline and compress the air within the crack. When the wave retreats, the air in the crack expands quickly causing a minor explosion. This process is repeated continuously. Corrosion This is the chemical action of sea water. The acids in the salt water slowly dissolve rocks on the coast. Limestone and chalk are particularly prone to this process. Processes of erosion – which shape the coastline
Types of coastal transportation Material eroded by the sea is carried within the water in a number of ways: 1.Minerals dissolved from rocks are carried in solution 2.Small rock fragments, light enough to be held within the water, float in suspension. 3.The largest rock fragments which are too heavy to be picked up by the waves, are transported by the process of traction. This is where they roll along the bed when the waves pick up enough energy. 4.Finally, medium sized rock particles, which cannot be carried by the waves all the time, are moved by saltation. This is where during times of higher wave energy the particles are picked up and then dropped again as the wave loses its energy.
This movement of sediment along the coastline is called longshore drift. Processes of transportation – LONGSHORE DRIFT
Landforms formed by erosion You need to know the formation of: 1.Cliffs 2.Wave cut platforms 3.Caves 4.Arches 5.Stacks 6.Headlands and bays
Cliff formation The erosion of a cliff is greatest at its base where large waves break - here hydraulic action, scouring and wave pounding actively undercut the foot of the cliff forming an indent called a wave-cut notch whilst the cliff face is also affected by abrasion as rock fragments are hurled against the cliff by the breaking waves. This undercutting continues and eventually the overhanging cliff collapses downwards as it becomes unstable- this process continues and the cliff gradually retreats and becomes steeper.
Formation of wave cut platform The base of the cliff is attacked by destructive waves, especially at high tide when they have more power. These erode the cliffs by hydraulic power and corrasion forming a wave-cut notch. This gets larger until the cliff collapses. As the process is repeated many times the cliff retreats leaving a wave-cut platform below (a sloping platform of sand, pebbles and rocks) exposed at low tide.
Caves, arches and stack formation
Headlands and Bays Sections of coastline which are particularly resistant to erosion (hard rock) stick out to form headlands. Weaker sections of coastline which are more easily eroded form bays. The waves are less powerful in bays as they are more sheltered, so deposition tends to dominate and explains why sandy beaches are common features.
Formation of depositional features Beaches are the main feature of deposition found at the coast, these consist of all the material (sand, shingle etc.) that has built up between the high and low tide mark. There are number of different sources of beach material - the main source being rivers, where fine muds and gravels are deposited at the river mouth. Other sources of beach material include longshore drift (bringing material from elsewhere along the coast); constructive waves (bringing material up the beach from the sea) and from cliff erosion.
Landforms formed by deposition - Spits A spit is an area of sand or shingle which either extends at a gentle angle out to sea or which grows across a river estuary e.g. Dawlish Warren, Devon. Many spits are characterised by a hooked or curved end. Spits develop where longshore drift moves large amounts of material along the beach and where there is a sudden change in the direction of the coastline. Where the coastline changes direction, sand and shingle are deposited, which builds upwards and outwards to form a spit. Occasionally when winds blow from a different direction, material will be pushed inland causing the spit to curve. Spits cannot grow across estuaries because of the speed of rivers flowing out to sea. Behind the sheltered water of the spits, salt marsh and mud creeks develops. coastline changes direction Winds from NW
Leisure facilities along spits Golf course Fishing Walking Nature reserves e.g. SSSI (Sites of Special Scientific Interest) Bird/animal watching e.g. grey seals Beaches Holiday parks Dawlish Warren
Bars Occasionally, longshore drift may cause a spit to grow across a bay, trapping a freshwater lake or lagoon behind it. This feature is called a bar e.g. Slapton, South Devon. In the UK, following ice melt at the end of the last ice age and sea level rise, some offshore bars have been driven onshore. This type of bar is called a barrier beach e.g. Chesil Beach, Dorset. Chesil Beach
Sea level rise Background Over the last 15 years, global sea levels have risen on average by 3mm a year. Latest estimates suggest that by the end of the century (2000), global sea levels will rise by between 28 and 42 cm. Since more than 70% of the world’s population live near the coast, the effects could be devastating. What are the causes? The main cause of sea-level rise is thermal expansion of seawater, as it absorbs more heat from the atmosphere (as a result of global warming). Incredibly, scientists believe that the melting of ice on land (e.g. Greenland) and at sea (e.g. Arctic) will have no direct effect on sea levels but it is the thermal expansion of sea water which will lead to sea level rises. What would be the impact of sea level rises? The impacts of sea level rising can affect countries/communities in 4 main areas: A.ECONOMIC (money)B.SOCIAL (people) C.ENVIRONMENTAL (natural world)D.POLITICAL (decision making)
Case study of sea level rise - Maldives 80% of the islands are only 1m above seal level. It is thought that sea levels are rising there about 9mm/year and that the entire population may have to abandon their homes by the end of the century. So, what would the impacts be? 1.ECONOMICALLY – fishing is the biggest industry but tourism comes a close second, thanks to its crystal clear water, beautiful beaches and tropical climate. Many people rely on these industries for jobs and income for their families. 2.SOCIALLY – the people fear that they are literally being washed away, which will force them to lose their home, jobs, culture and separate families. 3.ENVIRONMENTALLY – with the majority of the islands protected by only a barrier of coral, there is little to stop the advancing sea level rise and the flooding and loss of the islands forever.. 4.POLITICALLY – most decisions are taken locally by local government, police and fire services. An evacuation may be needed of many islands within 50 years. The Maldives government is appealing to countries to cut their carbon emissions and therefore reduce global warming and the consequential sea level rises associated with this.
Case study of recent cliff collapse – Holderness, E.Yorkshire Where is it? The Holderness Coast is on the east coast of the UK, facing the North Sea. What is the problem there? The coastline is mainly made up of cliffs (20-30m high), consisting of soft, easily eroded boulder clay. The cliff line is retreating at an alarming rate - greater than 1m / yr (fastest rate in Europe) - 4km of land have been lost since Roman Times, including many villages and farm buildings.
Why is cliff erosion such a problem here? 1.The cliffs are made up of soft glacial material (Boulder Clay - made up of sands and gravels). This is easily eroded by the waves and the cliffs are easily undermined. 2. The waves are mainly destructive - eroding the base of the cliffs (hydraulic action etc.) 3. Most of the material eroded from the cliffs is washed out to sea, the rest is moved by longshore drift - the beaches are therefore narrow and do little to protect the coastline. (If the beaches were wider, the waves would break on the beaches reducing their erosive power). What have the effects been on people and the environment? By 1998, the main road running through the village of Mappleton was only 500m from the cliff top and in places it is now only 50m 29 villages have been claimed by the sea in 1000 years Farmers are losing valuable farmland Holiday caravans have collapsed into the sea In June 1993 the Holbeck Hall Hotel slumped into the sea Easington Gas Station (a North Sea Gas Terminal) on top of the cliffs is under threat
How can coastlines be managed? Hard Engineering Hard engineering involves using man made structures to control the actions of the sea and protect property from flooding and erosion. However, they are less commonly used today, as they are expensive to build and maintain, as well as being visually obtrusive and unnatural. They tend to interfere with natural coastal processes and can cause problems further down a coastline e.g. erosion and cliff collapse. Soft Engineering Soft engineering approaches try to fit in and work with the natural coastal processes. They are often involve low maintenance costs and are environmentally more friendly and sustainable. They are usually the preferred option of coastal management. Managed retreat Managed retreat or coastal realignment is when some of the coastline is allowed to retreat. It is a viable option when there is a high risk of flooding or cliff collapse and when the land is of relatively low value e.g. poor quality grazing land.
A rip rap is rocks laid out as a ramp, with the largest and heaviest ones on the outside These large rocks reduce the energy of the waves and are relatively cheap Can be very expensive if you can’t use local rocks A sea wall is made of concrete and sometimes has a curved lip This structure reflects wave energy (they bounce off) and helps prevent flooding It is very expensive to replace a section of this after storms A groyne is a wooden barrier of planks at right angles to the shore This helps to stop material moving down the coast and helps build up a small beach This will rot after about 20 years and will need replacing Beach replenishment is when sand is brought from elsewhere to build up a beach This is a cheap way of building up the level of a beach The sea will eventually erode and transport the sand somewhere else A concrete breakwater is a platform made of concrete or rocks extending out to sea This helps to stop material moving down the coast and helps build up a large beach Places down the coast suffer from reduced material being transported and deposited Revetments are wooden slats laid out like a ramp underneath a cliff These help break up wave energy, so helping to protect a cliff These are not as strong as sea walls. Wood can be damaged in strong waves Gabions are cube shaped wire cages filled with rocks and large pebbles These are relatively cheap and can be easily fixed, as they are individually caged These are unattractive and have a relatively short life span (about 4 years) Methods of coastal protection (management)
Advantages and disadvantages of coastal protection schemes Advantages Wave energy is broken/absorbed/reflected Flooding is stopped e.g. sea wall – less chance of loss of money to businesses along beach e.g. cafes, restaurants, shops, amusements etc. Longshore drift is stopped e.g. by groynes, breakwaters resulting in the building up beaches, making more sand available to visitors/tourists/locals Residential housing and farmland is protected from cliff collapse Disadvantages Schemes are often ugly Noise pollution from construction High cost of construction e.g. sea wall Stopping longshore drift results in erosion somewhere else More tourists means more litter, more cars (congestion)
Managed retreat (costs and benefits) Case study: Wallasea Island, Essex Location: Wallasea Island is a low-lying coastal island formed at the confluence of the Rivers Crouch and Roach in Essex. What has happened? With the coastal defences in the north of the island crumbling away, the government decided to realign (change the shape of) the northern part of the island by constructing a new embankment (wall) inland (further south) and allow the sea to further break through (breach) the old sea defences.
Benefits: The new mudflats and salt marsh (created where the defences are breached – see photo) will help protect the new sea wall They will offer additional protection to the property to the south The scheme aims (still too early to assess) to bring back bird habitats which were lost to previous development, improve flood defences on the island and create new leisure opportunities Costs: The scheme cost taxpayers £7.5 million Sediment (mud) and vegetation (salt marsh) has not been immediate
For a coastal environment that you have studied, describe the environment and explain why it provides a suitable habitat for the species living there (Foundation) Dawlish Warren is a coastal spit, a narrow finger of land. It is an area of grassland, sand dunes, mud flats and beach that lies at the mouth of the River Exe. Behind the sand dunes is a nature reserve and it has been designated a SSSI (Site of Special Scientific Interest). It is important for wildfowl e.g. pheasants and wading birds e.g. geese, oystercatchers, as the birds arrive to escape the extreme cold winter of Northern Europe and also because the spit provides roosting (resting) beyond high tide levels. There are also many very special plants e.g. Sand Crocus, which can only grow as a result of the warm, sunny climate and low rainfall.
For a coastal environment that you have studied, describe the ways in which it is managed to ensure it is conserved, but used sustainably (Higher) Firstly, at Dawlish Warren, there is an education centre which provides information to students and the public about what they can do to care for the area. The centre will also cordon areas off e.g. at times of animal breeding and put signs up to ensure that habitats are protected when necessary e.g. damaged (trampled) sand dunes. Secondly, boardwalks have been put down to allow public access and use but also to try and stop people from tramping the dunes and vegetation in the area, therefore protecting them. Thirdly, the sand dunes have been planted with marram grass (has very long roots), so stabilising them for the future.
Useful websites for animations rev4.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/geography/coastal/coastalprocesses rev4.shtml (processes of coastal erosion) (formation of erosional landforms) (spit formation) Geography at the movies - (Coasts)