We have now come to the end of the Coasts Unit and its time to revise!
Here are some resources to help you.
Year 11 mind map:
COASTS - GCSE GEOGRAPHY
Check list of key concepts to revise:
1. Energy at the coast - types of waves and basic principles behind wave formation / factors affecting the strength of waves
2. Coastal Processes - erosion processes (you need to be able to describe the processes and how they work); transport processes (you must be able to talk through the process of longshore drift and it helps if you are able to draw an annotated diagram to show the process) and deposition
3. Coastal Erosion Landforms - you must be able to talk through both the features and formation of the following landforms: cliffs; wave-cut platforms; headlands and bays; caves, arches, stacks and stumps (in your description and explanation of formation always include some examples of named erosion processes that may be at work). You should also be able to draw annotated diagrams of the features to show how they form as well as knowing named examples of each.
4. Coastal Deposition Landforms - you must be able to talk through both the features and formation of the following landforms: beaches; spits; bars and tombolos. You should be able to draw annotated diagrams of the features to show how they form as well as knowing named examples of each.
5. Case Study of Coastal Erosion - learn (including detail - i.e. location, facts and figures) a case study of coastal erosion - Lulworth and Durdle Door.
6. Coastal Defence - you need to be aware of the options for coastal defence - hard engineering, soft engineering or managed retreat. You should be able to describe coastal management techniques and be able to discuss their advantages and disadvantages. You should learn a named case study to back this up - for example the Holderness coast / Holland.
Revision Resources:
- make good use of your class notes
- make use of your extended answers booklet and mind maps from G3
- make use of blog posts to consolidate your understanding / recap concepts you are less sure of - remember there are various links to animations etc. to help you.
-use the film from the Coast trip to revise erosional features
When managing the coastline there are two main options:
1. HARD ENGINEERING- this is where man made coastal defence structures are used to reflect large amounts of wave energy and hence protect the coastline.
2. SOFT ENGINEERING- this is where beaches or naturally formed materials are used to control / re-direct erosion processes.
You need to know examples of coastal management techniques and their advantages and disadvantages:
Hard Engineering Techniques:
1. Re-Curved Sea Wall- concrete wall which is curved on the underside to deflect the power of the waves- these can be very expensive (up to £1-2 million per km) and the deflected waves can scour material at the base of the wall causing them to become undermined- these are however a very effective means of preventing erosion and they reflect rather than absorb wave energy.
2. Rip Rap- large boulders on the beach absorb wave energy and break the power of the waves- although movement of the boulders is expensive this can be a much cheaper method than some other solutions- the boulders can however be undermined easily by waves washing away sand and shingle beneath them. They also can be quite ugly, changing the appearance of a coastline.
3. Groynes- these structures (usually either wooden or steel) are designed to stop longshore drift and therefore act to build up and anchor beach material, protecting the base of cliffs.- they are effective at reducing erosion in the area they are constructed in by causing significant build up of beach material- groynes may however starve areas further down the coast of material by stopping longshore drift, resulting in an increase in erosion in these areas
4. Gabions- these cages of boulders are built into cliff faces to protect the cliff from the force of the waves;- they are cheaper than sea walls and can be very effective where severe erosion is a problem- they are however visually intrusive
5. Revetments - these wooden structures break the force of waves and beach material builds up behind them- they are cheap and effective at breaking waves- as well as being visually intrusive however they do need replacing more frequently than most other defence methods.
Soft Engineering Techniques
Soft engineering includes beach replenishment in which beach material is added to provide a "natural solution".
Environmentally this is a preferred option as it maintains the beauty of the landscape and avoids visual intrusion, however it can be expensive to maintain as longshore drift continues to move beach material down the coast and therefore regular replenishment is required.Sand Dunes and salt marshes can also be encouraged to act as natural barriers to the waves.
Revision Time: Coastal Management at Sidmouth - What forms of coastal management can you see?
Sidmouth seafront west in England
Case Study of Coastal Erosion and Coastal Defence:
Where is the Holderness Coast? What is the problem?
View Larger Map
The Holderness Coast is on the NE coast of the UK, facing the North Sea. To the north one finds Flamborough Head (Headland) and to the south Spurn Head ( a Spit). This is a distance of roughly 60km. Hull is the closest city to Mappleton and is 17km east of it.
The coastline is mainly made up of cliffs (20-30m high), consisting of soft, easily eroded boulder clay. Where the cliff line meets the Humber Estuary, a spit has formed due to the change in the direction of the coastline - Spurn Head.
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.
Easington Gas Station (a North Sea Gas terminal) is situated on the cliffs top and its position is under threat.
Click here for an excellent Google Tour of the Holderness coastline (thanks to Simon Renshaw)
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 Holderness Coast is very exposed, approaching waves have a long fetch over the North Sea.
3. The waves are mainly destructive - eroding the base of the cliffs (hydraulic action etc.)
4. 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).
5. The coastline is threatened further by sea-level rise.
Attempts at Coastal Management along the Holderness Coast include:
-use of groynes to trap moving beach material and provide a protective beach in front of the cliff
-the construction of sea walls and revetments as wave-resistant structures at the base of the cliffs-artificial off-shore breakwaters like tyres and concrete blocks, forcing waves to break off-shore. -sea wall used to protect Easington Gas Station (cost £4.5 million)
-Due to extensive costs - only the most valuable areas of land are protected. Much of the area is farmland which is not protected.
Example of the impacts of Coastal Management: Mappleton
The village of Mappleton is greatly under threat by coastal erosion along the coastline and by 1998, the main road running through the village was only 500m from the cliff top and in places it is now only 50m. Mappleton is 3km south of Cowden. There are roughly 30 properties. The village is under threat due to the easily eroded boulder clay (glacial till) which makes up the cliff line. The area suffers from erosion rates of up to 1m per year.
Protecting Mappleton
To reduce the amount of erosion threatening Mappleton, 2 rock groynes were constructed in 1991 to encourage the build up of beach in front of Mappleton by trapping longshore drift. Rock armour was also placed at the foot of the cliffs to create a sea wall.
The following images show a rock groyne and rock armour (rip rap) which creates a sea wall and protects the cliffs.
This meant that that waves would break on the beach rather than attacking the cliffs.
Problems for further down coast - Cowden
Those living south of Mappleton village have experienced the 'knock-on' effects of the coastal management.
The groynes at Mappleton have disturbed the natural longshore drift movement, trapping the coastal material.
Therefore whilst material is still being moved south of Mappleton, there is no fresh sediment to replace it.
Beaches have become even narrower and the cliffs are unprotected.
Estimates suggest that it has accelerated cliff erosion south of Mappleton to 10m / yr.
Click here for excellent images from the Holderness coastline
Here is a video showing a farm south of the Mappleton rock groyne being lost to the sea
Follow this link to gather excellent information on Mappleton and the Holderness coastline in general
Mappleton Case Study Sheet
There are 4 main depositional features that you need to learn. These are:
1. Beaches
2. Spits
3. Bars
4. Tombolos
Beaches
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.As constructive waves build up beaches, they often form ridges in the beach known as berms. The berm highest up the beach represents the extent to which the water has reached during high tide.
Click on the diagram below to see the main sources of beach material
SPITSSpits are long narrow ridges of sand and shingle which project from the coastline into the sea.The formation of a spit begins due to a change in the direction of a coastline - the main source of material building up a spit is from longshore drift which brings material from further down the coast.Where there is a break in the coastline and a slight drop in energy, longshore drift will deposit material at a faster rate than it can be removed and gradually a ridge is built up, projecting outwards into the sea - this continues to grow by the process of longshore drift and the deposition of material.A change in prevailing wind direction often causes the end of spits to become hooked (also known as a recurved lateral).On the spit itself, sand dunes often form and vegetation colonises (for example Blakeney Point - North Norfolk)Water is trapped behind the spit, creating a low energy zone, as the water begins to stagnate, mud and marshland begins to develop behind the spit;Spits may continue to grow until deposition can no longer occur, for example due to increased depth, or the spit begins to cross the mouth of a river and the water removes the material faster than it can deposited - preventing further build up.
Examples of Spits-
Spurn Head - Holderness Coast
Hurst Castle Spit
Model answer on how spits are formed - shown as a "word cloud"
Click below for an annotated diagram of spit formation:
BARS
These form in the same way as a spit initially but bars are created where a spit grows across a bay, joining two headlands. Behind the bar, a lagoon is created, where water has been trapped and the lagoon may gradually be infilled as a salt marsh develops due to it being a low energy zone, which encourages deposition.
Example of a Bar: Slapton Sands - Devon.
TOMBOLOS
Tombolos are formed where a spit continues to grow outwards joining land to an offshore island.
Example of a Tombolo: - Chesil Beach - which joins the South Dorset coast to the Isle of Portland.
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REVISING COASTAL DEPOSITION FEATURES
Remember - as well as being able to describe the formation of each feature of coastal deposition, you should be able to give a named and located example e.g. a spit - Spurn Head (Holderness Coast). You should also try and learn a labelled diagram to show the formation of each feature.
- Beach - Dawlish Warren (Devon)
- Spit - Spurn Head (Holderness Coast)
- Bar - Slapton Sands (Devon)
- Tombolo - Chesil Beach (joining S Dorset Coast to Isle of Portland)
Having now learnt both erosion and deposition features you need to make sure that you can distinguish between them.
Coastal Erosion Features
There are 3 main groups of coastal features which result from coastal erosion:
1. Headlands and Bays
2. Caves, Arches, Stacks and Sumps
3. Cliffs and Wave-cut platforms
Before you revise the formation of these landforms, have a look at this video and make sure you are able to identify the landforms from their distinctive features.
1. HEADLANDS AND BAYS
Headlands are resistant outcrops of rock sticking out into the sea, whilst bays are indents in the coastline between two headlands.
So how do headlands form?
- Headlands form along discordant coastlines in which bands of soft and hard rock outcrop at right angles to the coastline.- Due to the presence of soft and hard rock, differential erosion occurs, with the soft, less resistant rock (e.g. shale), eroding quicker than the hard, resistant rock (e.g. chalk)- Where the erosion of the soft rock is rapid, bays are formed- Where there is more resistant rock, erosion is slower and the hard rock is left sticking out into the sea as a headland.- The exposed headland now becomes vulnerable to the force of destructive waves but shelters the adjacent bays from further erosion.Named Examples of Headlands and Bays: (LEARN!)The Dorset coast has excellent examples of Headlands and Bayse.g. Swanage Bay and the Foreland (a headland)
2. CAVES, ARCHES, STACKS and STUMPS
Once a headland has formed it is then exposed to the full force of destructive waves and it gradually begins to erode. you need to be able to describe the erosion of a headland and the features that form.For the sequence of formation see the animation below:
So how does a headland erode and caves, arches, stacks and stumps form?
- Firstly, the sea attacks the foot of the cliff and begins to erode areas of weakness such as joints and cracks, through processes of erosion such as hydraulic action, wave pounding, abrasion and solution;
- Gradually these cracks get larger, developing into small caves;
- Further erosion widens the cave and where the fault lines runs through the headland, two caves will eventually erode into the back of each other forming an arch, passing right through the headland.
- A combination of wave attack at the base of the arch, and weathering of the roof of the arch (by frost, wind and rain), weakens the structure until eventually the roof of the arch collapses inwards leaving a stack, a stack is a column of rock which stands separate from the rest of the headland.
- The stack will continue to erode, eventually collapsing to form a stump which will be covered by water at high tide.
Named Examples:The Foreland (Dorset Coastline) is a great example of a headland which shows these features - there is a distinctive stack called Old Harry and a stump known as Old Harry's Wife.
A good example of a distinctive arch, also found on the Dorset Coast is Durdle Door.
3. CLIFFS AND WAVE-CUT PLATFORMS
Cliffs are steep rock faces along the coastline, they tend form along concordant coastlines with resistant rocks parallel to the coast.
So how do cliffs and wave-cut platforms form?
- 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 - this process continues and the cliff gradually retreats and becomes steeper.
- As the cliff retreats, a gently-sloping rocky platform is left at the base, this is known as a wave-cut platform which is exposed at low tide.
Named Examples:Good examples of cliffs and wave-cut platforms can be found at Hunstanton (North Norfolk) and Flamborough Head (Yorkshire)-------------------------------------------------------------------------------
REVISING COASTAL EROSION FEATURES
Remember - for each erosion feature try and learn a labelled diagram to show its formation, make sure that you also mention examples of erosion processes when describing how the features are actually formed. Finally to access the highest marks remember to name and locate examples of each feature.
- Swanage Bay (Dorset Coast)
- The Foreland (Headland) (Dorset Coast)
- Old Harry (Stack) (Dorset Coast - off of the Foreland)
- Old Harry's Wife (Stump) (Dorset Coast - off of the Foreland)
- Durdle Door (South Dorset Coast)
- Cliffs and Wave-cut platforms - Flamborough Head (Yorkshire)
Remember, there are 3 main processes that cause a coastline to change:
1. Erosion
2. Transport
3. Deposition.
There are number of factors which affect each of these processes - we are going to start by exploring erosion processes and the factors that can affect the amount of erosion that may take place along a coastline.
COASTAL EROSION
Erosion Processes:
Erosion is the wearing away of rocks, at the coast there are 6 main types of erosion processes in action :
1. ABRASION (this is also known as corrasion) - this is where rock fragments are hurled at cliffs by breaking waves, gradually scraping away at the cliff face;
2. HYDRAULIC ACTION - as waves break against the cliff face, the pressure of the breaking wave can compress air in cracks. This compressed air gradually forces open the crack in the rock - as this process continues, the rock becomes increasingly weakened.
3. SOLUTION (this is also known as corrosion) - this occurs where the salt water is able to dissolve some of the chemicals in rocks - for example, limestone cliffs are gradually weakened as the salt water dissolves the calcium carbonate in the limestone.
4. SCOURING - this occurs at the base of the cliff as the waves break and swirl around, gradually removing loose rock.
5. ATTRITION - this is where rock fragments carried by the waves hit against each other and gradually wear down to form sand and silt
6. WAVE POUNDING - the sheer force of waves hitting against the cliff face
These processes of erosion form a series of distinctive landforms at the coast.
Rates of Coastal Erosion
So what are the factors that determine how much erosion can take place at the coast?
1. The Resistance of the Rocks - e.g. limestone, chalk and granite are resistant rocks (often forming cliffs and headlands) and erode relatively slowly, whilst less resistant rocks such as clay are easily eroded.
2. The Strength of the waves - affected by the wind strength and duration and its fetch
3. The shape of the coastline (which is dependent on its geology) - on concordant coastlines, rocks are parallel to the wave front and therefore rates of erosion are similar along the coastline. On discordant coastlines, differential erosion may occur, where bands of hard and soft rock outcrop at right angles to the sea. Consequently headlands and bays form along discordant coastlines and whilst headlands remain exposed to the force of the waves, bays are sheltered.
Look at the diagram below for a summary of factors affecting coastal erosion.
COASTAL TRANSPORT
The second process operating at the coast is transport. Material eroded by the sea is carried within the water in a number of ways, minerals dissolved from rocks are carried in solution, whilst small rock fragments, light enough to be held within the water, float in suspension. 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. 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 looses its energy.
The main form of transport operating at the coast is that of LONGSHORE DRIFT.
Longshore drift is the process by which sand and pebbles are moved along a beach by the movement of the waves.
Watch the following film to revise:
COASTAL DEPOSITION
Material is moved up the beach by the swash at an angle which is controlled by the prevailing wind. The backwash then carries material back down the beach at right angles to the coastline under the influence of gravity. Gradually the material is moved along the coastline, its direction being controlled by the prevailing wind direction.The final process operating at the coast is that of deposition - this is where material that is too heavy to be transported any more is left behind, building up the beach. Due to the importance of energy in transporting sand and shingle, it is the largest material that is deposited first. A number of distinctive features may form due to coastal deposition.
Follow up links:
Animations of Coastal Erosion Processes (BBC Bitesize)
Transport and Deposition (BBC Bitesize)
Key Terms Check:
Erosion - the wearing away and removal of material
Deposition - the dropping of material
Abrasion - the wearing of rock due to rock fragments being hurled against cliffs
Attrition - the breakdown of rocks as they hit against each other
Hydraulic Action - the force of waves causing rocks to split apart as waves compress air in cracks in the rocks
Wave Pounding - sheer force of water hitting rocks
Solution - where minerals in rocks are dissolved by the action of sea water
Scouring - occurs where water and broken rock fragments swirl around at the base of cliffs gradually wearing rock away.
Longshore Drift - the movement of material along a coastline
Podcast: Coastal ProcessesYou can listen to a podcast of this post below - to download a copy to listen to on your .mp3 player click here.
The coast represents the meeting point between the land and sea. Coasts are very dynamic areas and they are constantly change. This change is due to 3 main processes which operate at the coast, 1. Erosion; 2. Transport and 3. Deposition. These 3 processes are all driven by the amount of energy that is available at the coast. The main agents of change at the coasts are waves. Waves are movements of energy throughout the water, but where do waves get their energy from? The answer to this is wind.
As wind blows over the surface of the sea, it creates friction. This frictional drag causes water particles to begin to rotate and energy is transferred forward in the form of a wave. Whilst the water moves forward, the water particles return to their original position. As a wave reaches shallow water, friction between the sea bed and the base of the wave causes the wave to begin to slow down and its shape becomes more eliptical. The top of the wave however, unaffected by the friction, becomes steeper until it eventually breaks. When the wave breaks, water washes up the beach, this is called the swash. The movement of water backdown the beach is called the backwash.It is the rate at which waves reach the coast which determine whether the main process acting on the coastline is erosion or deposition.There are two main types of waves:(i) CONSTRUCTIVE WAVES - tend to arrive at the coast at a rate of less than 8 waves per minute, they are low energy waves and are small in height. They have a strong swash and a weak backwash. This means that constructive waves tend to deposit material and build up a beach.
(ii) DESTRUCTIVE WAVES , have much higher energy and tend to arrive at the coast at a rate of more than 8 per minute. They are much larger in height often having been caused by strong winds and a large fetch. These high energy waves have a weak swash but a strong backwash, which erode the beach but pulling sand and shingle down the beach as water returns to the sea.
There are 3 main factors which will affect the strength of a wave and therefore whether it is more likely to erode or build up the coastline:
(i) the strength and speed of the wind - the faster the wind, the more energy is transferred and therefore the bigger the wave that is produced.
(ii) the duration of the wind - this is the length of time for which the wind has blown - the longer the wind blows, the more energy is transferred to the wave
(iii) the fetch - this is the distance over which the wind has blown and therefore how far the wave has travelled. The longer the fetch, the larger the wave is likely to be.
Follow up links:
Excellent Animation showing a wave forming and breaking (Wycombe High School)Wave Machine Simulator - create your own ocean wave
Ocean Surface Wave - WikipediaWaves - includes animation of swash and backwash (BBC Bitesize)
Constructive and Destructive Waves Animation (Wycombe High School)
Key Term Check:
Swash - the movement of water and material up the beach (in direction of prevailing wind)Backwash - the movement of water and material back down the beach (straight back down due to gravity
Constructive wave - low energy wave with greater swash than backwash - tends to build up the beach
Destructive wave - high energy wave with greater backwash than swash - tends to erode beach
Podcast: Energy at the Coast - Wave FormationYou can listen to a podcast of this post below - to download a copy to listen to on your .mp3 player click here.
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