Presentation on theme: "Coasts Revision: The boundary (interface) between the land and the sea Unit 1: section B In the physical paper you will have to answer 3 questions; 1 on."— Presentation transcript:
Coasts Revision: The boundary (interface) between the land and the sea Unit 1: section B In the physical paper you will have to answer 3 questions; 1 on water on the land, 1 on the restless earth and 1 on the coastal zone. The paper is 1:30hrs long therefore you should aim to spend 30 minutes on each question.
The Syllabus Opposite is a copy of the syllabus for this unit of work. It should help you to highlight any gaps in your notes and learning.
Main Case Studies Mappleton on the Holderness Coastline, East Yorkshire A case study of an area of recent or threatened cliff collapse – rates of coastal erosion; reasons why some areas are susceptible to undercutting by the sea and collapse; how people may worsen the situation; the impact on people’s lives and the environment. London and the Thames Estuary A case study to illustrate the likely economic, social, environmental and political impact of coastal flooding. The Essex Marshes A case study of a coastal habitat – its environmental characteristics; the resulting habitat and species that inhabit it and reasons why. Strategies to ensure the environment is conserved, but also allow sustainable use of the area. A case study of coastal management to assess the costs and benefits of strategies adopted. Soft Engineering Hard Engineering
Key idea no.1 The coast is shaped by weathering (mechanical and chemical), mass movement (sliding and slumping), erosion (caused by destructive waves via hydraulic power, abrasion, attrition and solution), transportation (by longshore drift in the main, but also traction, saltation, suspension and solution) and deposition caused by constructive waves.
Understanding Waves How are they formed? Wind blowing over the sea causes ripples in the water which eventually get bigger and form waves. The size and energy of a wave is influenced by: 1.the length of time that the wind has been blowing 2.the strength of the wind 3.how far the wave has travelled (called the fetch)
What happens to the wave when it reaches the shore? When a wave approaches the coast its lower part is slowed by friction with the sea bed, but the upper part continues to move forward. As it is left unsupported, it topples over (the crest collapses) and breaks forward against the beach or cliff.
Constructive waves Constructive or swell waves Helps build up beach material Strong swash Weak backwash Relatively flat and occur where beaches are gently sloping Long wavelength Small wave height (1m>) Crests over 20m apart operate in calm weather are less powerful than destructive waves
Destructive waves Removes beach material Weak swash High wave in proportion to length Strong backwash Short wavelength Tall (1m<) operate in storm conditions are created from big, strong waves when the wind is strong and has been blowing for a long time Can you annotate this diagram of a destruction wave to show its main features?
Exam Question The examiner says… Any 2 valid differences relating to the frequency, steepness, height, relative importance of swash/backwash. Give two differences between destructive waves and constructive waves (2 marks)
Weathering This is the breakdown of rocks at or near the surface. There are 3 types: Mechanical This leads to the breakdown of rock without any change in the minerals that form the rock. 1.Freeze Thaw 2.Onion Skin (sometimes called exfoliation) Chemical This happens when the rock’s mineral composition is changed, leading to the disintegration of the rock. It is caused by the weak carbonic acid present in rainfall and can affect limestone in particular. Biological This is caused by plants and animals and can act to speed up the rate of mechanical weathering. But how? Task: Go to page 29 in Understanding GCSE Geography. How does biological weathering take place?
There are 4 processes of erosion Hydraulic Power Corrasion/abrasion Attrition Corrosion Learn these processes and be prepared to explain how they erode the coast (see the orange box at the top of page 117 in Understanding GCSE Geography). If the examiner wanted to question you about these processes, how might they do it? Think about the command words used.
Key idea no. 2 Distinctive landforms result from different processes. These can be divided into those caused by erosion and those caused by deposition.
Landforms of costal erosion Cliffs (e.g. the white cliffs of Dover) Wave cut notch Wave cut platforms Stacks Stumps Caves Arches Headlands Bays You must be able to draw and annotate diagrams to show how these features are formed. Common mistakes include forgetting to 1.describe which type of waves and processes of erosion are acting on the rock 2.include examples with detailed diagrams that are in the correct sequence with complete/full annotations 3.Use a wide range of key terms E.g. Old Harry’s rocks in Dorset
Cliffs One of the most common features of the coastline in Britain and around the world are cliffs. Cliffs are shaped through a combination of erosion and weathering. The weather attacks the cliff top. The waves attack the cliff foot, causing a wave-cut notch at the bottom. Soft rock erodes easily and creates gently sloping cliffs. Hard rock is more resistant and erodes slowly and creates steep cliffs. weatheringresistant Waves attacking the cliff foot, causing a wave-cut notch at the bottom. The top of the cliff, weakened by the weather and the notch beneath it, eventually collapses. The debris is removed by the sea. This process means the cliff face gradually retreats.
Headlands and bays Another group of features shaped by erosion are headlands and bays. Headlands are formed when the sea attacks a section of coast consisting of alternating bands of hard and soft rock. The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant hard rock, such as chalk. This leaves a section of land jutting out into the sea; this is called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays.erosion Coasts where the geology alternates between strata (or bands) of hard rocks and soft rocks is called a discordant coastline. Discordant coastlines will have alternating headlands and bays. Concordant coastline is where the rock remains the same along the coastline. Concordant coastlines tend to have less bays and headlands. Along the coastline of the Isle of Purbeck in Dorset (south coast of England), there are both discordant and concordant coasts. The discordant coast has been formed into Studland Bay (soft rock), Ballard Point (hard rock), Swanage Bay (soft rock) and Durlston Head (hard rock). After Durlston Head the rock remains hard. This concordant coast has less features.geology
Discordant coastline Headland Bay
Using diagrams to help you, explain how a cliff and wave cut platform are formed (6 marks)
Cracks, joints and faults are the first lines of weakness to be exploited by destructive waves and processes of erosion like hydraulic action/abrasion Cave Arch Stack Stump Wave cut platform
Things to ask yourself What kinds of waves will erode the rocks? What are the features of these waves? What are the main processes of erosion acting on the shoreline? What part of the cliff will be attacked first? What will happen as the wave cut notch increase in size?
What is the examiner looking for? Level 3: Detailed (5-6 marks) Knowledge of accurate information appropriately contextualised and/or at correct scale Detailed understanding, supported by relevant evidence Well organized, demonstrating detailed linkages and the inter-relationships between factors Clear and fluent expression of ideas in a logical form (the sequence of events is accurate); uses a wide range of specialist terms where appropriate Accurate use of spelling, punctuation and grammar Text is legible
Model Answer? Waves are particularly good at exploiting any weakness in a rock, such as a joint. Erosion begins at the foot of a cliff where continual pounding by destructive waves may form a wave cut notch. By the same process of erosion, and particularly by hydraulic power and corrasion, any vertical line of weakness may be increased in size into a cave. However, the rock needs to be relatively hard or resistant otherwise it will collapse before the cave is formed. Once a cave has formed, when a wave breaks, it blocks off the face of the cave and traps air within it..
This compresses the air trapped inside the cave, which increases the pressure on the roof, back and sides. If the cave forms part of a narrow headland, the pressures from the waves may result in the back of the cave being pushed through to the other side so that it is open at both sides. The cave then becomes a natural arch. The base of the arch is attacked by waves, putting more and more pressure on the top of the arch. After continued erosion, especially if there is a weak point at the top of the arch, the arch collapses and becomes a stack. The stack is a piece of rock isolated from the main coastline.
There is a sequence of features formed in this process of erosion – notch, cave, arch and stack. However, the stack itself is attacked by waves from all sides. It is gradually reduced in size and eventually it collapses so that all the signs of where the coastline used to lie disappear. When you look at a map of the present day coastline therefore, it is important to remember that it may be many kilometres further back that it used to be.
ORIGINAL CLIFF FACE CLIFF RETREATS PRESENT CLIFF FACE WAVE CUT NOTCH WAVE CUT PLATFORM HIGH WATER MARK
2. Annotate these diagrams to show the formation of a stack (series of diagrams)
Transport and deposition of material along the coast Traction; saltation; suspension; solution (know these) Long shore Drift (LSD) – be able to draw and explain this diagram
Landforms of coastal deposition Beaches Spits (e.g. Spurn Head) – remember that sometimes these have a hooked end caused by the secondary wind. Spits develop in calm water where there has been a natural bend in the coastline causing deposition to occur from LSD. Salt marshes/Mudflats - can form behind a spit What you will have to do: –Recognise, describe and explain the formation of these features
Beaches Beaches are one of the most common features of a coastline. They are gently sloping areas of land between the high and low water marks. They are made up of eroded material that has been transported from elsewhere and deposited by the sea. If the geology of the area is particularly weak, erosion will take place meaning that waves (constructive) will be heavily laden with material adding to the size of the beach.
The formation of a spit (e.g. Spurn Head )
Bars A bar is a long stretch of beach material (sand or shingle) that joins together two headlands. A lagoon usually forms behind the bar. An example of a sand bar is Slapton Ley in Devon.lagoon Question: how are bars different to spits?
Key idea no.3 Rising sea level will have important consequences for people living in the coastal zone.
The rate of coastal erosion and frequency of flooding is expected to increase. 1.Global Warming 2.This causes more energy to drive Atlantic depressions which will produce strong wind and storm events 3.Recovery from the last ice age
London and Thames estuary Using page 128 in Understanding GCSE Geography What happened to London in 1953? What impacts did this have? What would the likely impacts of a similar event happening today? Why is the Thames Barrier considered unsustainable? Economic Political/SocialEnvironmental The effects can be split into:
Key idea nos. 3 and 4 Coastal erosion can lead to cliff collapse. This causes problems for people and the environment (e.g. Holbeck Hotel, Scarborough). There is discussion about how the coast should be managed. There is debate about the costs and benefits of ‘hard’ and 'soft’ engineering.
You need to be able to describe and explain how each one works (there are others) and their advantages and disadvantages.
Key idea no. 5 Coastal areas provide a unique environment and habitat. There is a need for conservation and this leads to conflict with other land uses.
The Essex Marshes The Essex Marshes are to be found all along the Essex coast from the River Thames in the south, at the border with Greater London, to the River Stour and Harwich in the north on the border with Suffolk. Essex has the longest coastline of any English county. A straight line drawn parallel to the coast from the Thames in the south to the Stour in the north is about 50 miles in length but follow the convolutions of the coastline and you will cover nearer 400 miles.
It is a mixed landscape of mudflats, sand and shingle banks, salt marsh, coastal grassland and sea walls. It is one of the top 5 wetlands in Britain interns of its value to wildlife. It provides valuable habitats for marine life (shore crabs and herring), birds feeding on the marshes (redshank and oystercatcher), and salt loving marsh plant communities (marsh samphire). The Essex Marshes
Under Threat! Farmers have gradually reclaimed land from the sea during g the last 400 years. Seas walls were built first to allow grazing, and later arable farming. Only about 2500 hectares of natural coastal marsh remain, compared to 30 000 hectares in 1600. Human threats from urban development and physical threats from coastal erosion are also a big problem.
Conservation of the marshes Deliberately allowing rising sea levels to flood large areas by making gaps in existing sea defences (DEFRA destroyed 300 metres of sea wall). Advantages will include safeguarding existing wildlife; acting as a buffer zone against flooding; making inhabited areas further inland safer; increasing areas that are useful habitats as natural nurseries for fish ; attracting bird species back to Britain. THIS IS AN EXAMPLE OF MANAGED RETREAT
Past paper questions 1.Describe 1 process of coastal erosion (2 marks) 2.Name the 3 types of landform resulting from coastal erosion (3 marks) 3.Explain how 2 coastal defences work (4 marks) 4.Explain how the coast is being protected at Mappleton East Yorkshire, from erosion by the sea (4 marks) – see next slide 5.Chesil Beach has been formed partly as a result of longshore drift. With the help of a diagram, explain how longshore drift works (6 marks) 6.Explain the formation of a wave-cut platform (6 marks) 7.For an area you have studied, explain the likely impacts that coastal flooding may have (6 marks) 8.For a coastal habitat that you have studied, explain why it is important and why it is under threat. (6 marks)
Tips! Learn all key terms Be familiar with diagrams and be prepared to draw and annotate them Give evidence to support your case studies Visit the GCSE Bite Size website and revise the COASTS section (be aware that the syllabus has changed slightly – the physical processes are still the same though as is the Mappleton case study). See me/ log on to http://www.aqa.org.uk/qual/gcse/geo_a_assess.php for past papers http://www.aqa.org.uk/qual/gcse/geo_a_assess.php
Glossary of Key Terms Abrasion – waves erode coastline by throwing pebbles against cliff faces Arch – rocky opening through a headland formed by wave erosion Bar – ridge of sand or shingle across the entrance to a bay or river mouth Beach – sloping area of sand and shingle between the high and low water marks Boulder clay/till – all materials deposited by ice, usually clay containing sharp-edged boulders of many sizes Cave – hollow at the bottom of a cliff eroded by waves Cliff – steep rock outcrop along a coast Constructive wave – gently breaking wave with a strong swash and weak backwash Destructive wave – powerful wave with a weak swash and strong backwash Effects – primary (first effects) and secondary (later effects), positive (good) and negative (bad) Erosion processes – wearing away the land surface by hydraulic action, abrasion, attrition and solution Flooding – water covering land that is normally dry after a river bursts its banks Hard engineering strategies – strong construction methods to hold floodwater back or keep it out
Glossary of Key Terms Hazard – natural hazards are short-term events that threaten lives and property Hazard (climatic) – short-term weather event that threatens lives and property Hydraulic power – erosion of rocks by the force of moving water in waves Managed retreat – abandon defence of present coastline in a controlled manner Marginal land – areas of land previously not considered good enough to be worth using Responses – actions immediately after the event or in the long-term Soft engineering strategies – more natural ways to reduce the impact of flooding on humans, with less intervention and more preparation Spit – ridge of sand or shingle attached to the land, but ending in open sea Stack – pillar of rock surrounded by sea, separated from the coastline Wave-cut platform – gently sloping surface of rock, in front of cliffs, exposed at low tide Weathering – breakdown of rock in the place where it outcrops (in situ)