Presentation on theme: "Coasts Revision: The boundary (interface) between the land and the sea"— Presentation transcript:
1Coasts Revision: The boundary (interface) between the land and the sea Unit 1: section BIn 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.
2The 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.
3Hard EngineeringMappleton on the Holderness Coastline, East YorkshireA 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 impacton people’s lives and the environment.London and the Thames EstuaryA case study toillustrate the likely economic, social, environmental and political impact of coastal flooding.Main Case StudiesSoft EngineeringThe Essex MarshesA case study of a coastal habitat – itsenvironmental characteristics; the resulting habitatand 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 managementto assess the costs and benefits of strategiesadopted.
4Key idea no.1The 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.
5Understanding 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:the length of time that the wind has been blowingthe strength of the windhow far the wave has travelled (called the fetch)
8What 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.
9Constructive waves operate in calm weather Constructive or swell wavesHelps build up beach materialStrong swashWeak backwashRelatively flat and occur where beaches are gently slopingLong wavelengthSmall wave height (1m>)Crests over 20m apartoperate in calm weatherare less powerful than destructive waves
10Destructive waves Destructive waves Removes beach material Weak swash High wave in proportion to lengthStrong backwashShort wavelengthTall (1m<)operate in storm conditionsare created from big, strong waves when the wind is strong and has been blowing for a long timeCan you annotate this diagram of a destruction wave to show its main features?
11Exam QuestionGive two differences between destructive waves and constructive waves (2 marks)The examiner says… Any 2 valid differences relating to the frequency, steepness, height, relative importance of swash/backwash.
12WeatheringThis is the breakdown of rocks at or near the surface. There are 3 types:MechanicalThis leads to the breakdown of rock without any change in the minerals that form the rock.Freeze ThawOnion Skin (sometimes called exfoliation)ChemicalThis 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.BiologicalThis 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?
13There are 4 processes of erosion If the examiner wanted to question you about these processes, how might they do it? Think about the command words used.Hydraulic PowerCorrasion/abrasionAttritionCorrosionLearn 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).
14Key idea no. 2Distinctive landforms result from different processes. These can be divided into those caused by erosion and those caused by deposition.
15Landforms of costal erosion Cliffs (e.g. the white cliffs of Dover)Wave cut notchWave cut platformsStacksStumpsCavesArchesHeadlandsBaysYou must be able to draw and annotate diagrams to show how these features are formed. Common mistakes include forgetting todescribe which type of waves and processes of erosion are acting on the rockinclude examples with detailed diagrams that are in the correct sequence with complete/full annotationsUse a wide range of key termsE.g. Old Harry’s rocks in Dorset
16CliffsOne 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.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.
17Headlands and baysAnother 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.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.
19Using diagrams to help you, explain how a cliff and wave cut platform are formed (6 marks) Turn projector off at this point and draw diagram
20Cracks, joints and faults are the first lines of weakness to be exploited by destructive waves and processes of erosion like hydraulic action/abrasionStackArchCaveStumpWave cut platform
21Things 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?
22What is the examiner looking for? Level 3: Detailed (5-6 marks)Knowledge of accurate information appropriately contextualised and/or at correct scaleDetailed understanding, supported by relevant evidenceWell organized, demonstrating detailed linkages and the inter-relationships between factorsClear and fluent expression of ideas in a logical form (the sequence of events is accurate); uses a wide range of specialist terms where appropriateAccurate use of spelling, punctuation and grammarText is legible
23Model 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..
24This 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.
25There 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.
272. Annotate these diagrams to show the formation of a stack (series of diagrams)
28Transport 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
29Landforms of coastal deposition BeachesSpits (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 spitWhat you will have to do:Recognise, describe and explain the formation of these features
30BeachesBeaches 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.
32BarsA 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.Question: how are bars different to spits?
33Key idea no.3Rising sea level will have important consequences for people living in the coastal zone.
34The rate of coastal erosion and frequency of flooding is expected to increase. Global WarmingThis causes more energy to drive Atlantic depressions which will produce strong wind and storm eventsRecovery from the last ice age
35London and Thames estuary The effects can be split into:London and Thames estuaryEconomicUsing page 128 in Understanding GCSE GeographyWhat 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?EnvironmentalPolitical/Social
36Key idea nos. 3 and 4Coastal 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.
37You need to be able to describe and explain how each one works (there are others) and their advantages and disadvantages.
38Key idea no. 5Coastal areas provide a unique environment and habitat. There is a need for conservation and this leads to conflict with other land uses.
39The Essex MarshesThe 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.
40The Essex MarshesIt 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).
41Under 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 hectares in Human threats from urban development and physical threats from coastal erosion are also a big problem.
42Conservation 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 RETREATDEFRA – Department for Environment, Farming and Rural Affairs RSPB – The Royal Society for the protection of birds
43Past paper questions Describe 1 process of coastal erosion (2 marks) Name the 3 types of landform resulting from coastal erosion (3 marks)Explain how 2 coastal defences work (4 marks)Explain how the coast is being protected at Mappleton East Yorkshire, from erosion by the sea (4 marks) – see next slideChesil Beach has been formed partly as a result of longshore drift. With the help of a diagram, explain how longshore drift works (6 marks)Explain the formation of a wave-cut platform (6 marks)For an area you have studied, explain the likely impacts that coastal flooding may have (6 marks)For a coastal habitat that you have studied, explain why it is important and why it is under threat. (6 marks)
45Tips! Learn all key terms Be familiar with diagrams and be prepared to draw and annotate themGive evidence to support your case studiesVisit 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 for past papers
46Glossary of Key TermsAbrasion – waves erode coastline by throwing pebbles against cliff facesArch – rocky opening through a headland formed by wave erosionBar – ridge of sand or shingle across the entrance to a bay or river mouthBeach – sloping area of sand and shingle between the high and low water marksBoulder clay/till – all materials deposited by ice, usually clay containing sharp-edged boulders of many sizesCave – hollow at the bottom of a cliff eroded by wavesCliff – steep rock outcrop along a coastConstructive wave – gently breaking wave with a strong swash and weak backwashDestructive wave – powerful wave with a weak swash and strong backwashEffects – 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 solutionFlooding – water covering land that is normally dry after a river bursts its banksHard engineering strategies – strong construction methods to hold floodwater back or keep it out
47Glossary of Key TermsHazard – natural hazards are short-term events that threaten lives and propertyHazard (climatic) – short-term weather event that threatens lives and propertyHydraulic power – erosion of rocks by the force of moving water in wavesManaged retreat – abandon defence of present coastline in a controlled mannerMarginal land – areas of land previously not considered good enough to be worth usingResponses – actions immediately after the event or in the long-termSoft engineering strategies – more natural ways to reduce the impact of flooding on humans, with less intervention and more preparationSpit – ridge of sand or shingle attached to the land, but ending in open seaStack – pillar of rock surrounded by sea, separated from the coastlineWave-cut platform – gently sloping surface of rock, in front of cliffs, exposed at low tideWeathering – breakdown of rock in the place where it outcrops (in situ)