1701718
Description
Flashcards by Chima Power, updated more than 1 year ago
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Created by Chima Power
about 10 years ago
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| Question | Answer |
| Destructive waves | Mainly responsible for coastal erosion and for taking sediment away from coastlines. Characteristics: backwash stronger than swash, break frequently between ten and fifteen every minute, high in proportion to length, generally found on steep beaches, short wavelength. |
| Constructive waves | Responsible for depostition in coastal areas. Number of characteristics: swash more powerful than backwash, break infrequently at a rate of ten or fewer per minutes, long in relation to height, usually found on gentle slopping beaches, long wavelength. |
| Hydraulic action | Pressure of the water being thrown against the cliffs by the wave. Also includes compresssion of air in cracks; as water gets into cracks in the rock face, compresses air in cracks, this puts even more pressure on the cracks and pieces of rocks break off. |
| Corrasion | Sand and pebbles carried within waves thrown against the cliff face with considerable force, particles break off more rocks, which in turn, are thrown against the cliff by the breaking wave. |
| Corrosion (solution) | Chemical reaction between different rock types and salt and other acids in seawater. Particularly evident on limestone and chalk cliffs where the water is a milkly blue at the bottom of the cliffs due to dissolved lime. |
| Attrition | Slightly different process that involves the wearing away of the rocks which are in the sea. As boulders in the sea continually roll around, they chip away at each other until smooth pebbles or sand are formed. |
| Waves | Formed when wind causes friction at surface of sea, causing a swell in wave circular motion. Swash is when waves hit land, backwash is when waves come go back out. Length of water the wind blows over is called the fetch. Amount of energy in wave determined by length of fetch, strenth of wind, length with which wind blows. |
| Physical weathering | Freeze thaw weathering or frost action is when water gets into cracks rocks, when the temperature falls below freezing, the water will expand as it turns to ice. Puts pressure on rocks around it and fragments of rock break off. Common in highland areas where temperature is below freezing during night and above during day. |
| Chemical weathring | Rainwater contains weak acids that can react with certain rock types. Carbonates in limestone are dissolved by these weak acids that can react with certain rock types and cause the rock to break up or disintegrate. Can be seen on limestone statues or limestone pavements. |
| Biological weathering | This the action of plants and animals on the land, seeds that fall into cracks in rocks will start to grow when moisture is present. Roots of the young plant puts out force their way into cracks and, in time, can break up rocks. Burrowing animals, such as rabbits, can also be responsible for the further break up of rocks. |
| Mass movement | This is when material moves down a slope due to gravity usually involving very large amounts of material. There are many different types of this process. |
| Soil creep | This is the slowest movement of soil with gravity pulling the water contained within the soil down a slope. The soil moves downward in conjunction with the water, because its so slow it isn'tpossible to identify the occurance. However the movement is much faster through periods and after periods of heavy rainfall. Moreover the slope may seem rippledd these are known as terracettes. |
| Slumping | Comon on the cost also known as rotational slipping involves a large area of land moving down a slope. Due to nature of slip curved surface are formed common on clay cliffs. During dry weather clay contracts and cracks; when it rains, the water runs into the cracks and is absorbed until the rock becomes saturated. Weakens the rock and due to pull of gravity slips down the slip and on its slip plane. |
| Headlands and bays | occurs on coastline where rocks of different resistances are at right angle to sea. Bays less resistant rock and indentations in the land. Headlands more resistant rock and protrude into the sea. Bays eroded at faster rate at first as less resistant overtime as cuts back waves reaching the coast are less powerful as they must travel over a longer expanse of beach. At such a point headlands further out at sea start to experience more powerful waves and are eroded at a faster rate than beforehand. |
| Cliffs and wave cut platforms | Headlands are usually formed from cliffs, when the sea moves against the base of the cliff from abrasion and hydraulic action( if rock type limestone or chalk corrosion) undercuts the cliff and forms a wave cut notch. Above an overhang will form overtime will fall into sea due to pressure of weight and gravity. More notches formed such cliff retreats becoming higher and steeper. Remains of cliff rock below the sea at high tide form a rocky wave cut platform. Due to erosion and weathering some boulders will have fallen from the cliff onto the platform. As width of platform increases so the power of the waves decreases as they have further to travel to reach the cliff. |
| Caves, arches, stacks and stumps | Formed in rocks will fault. Action of the sea exploits fault by erosion, hydraulic action. Fault widen in time to form cave if fault on headland will form caves on both sides. When back of caves meet arch is formed. Sea continue to erode bottom of arch plus weathering takes place on bare rock faces. As the sea undercuts the bottom of the arch, a wave cut notch will form. Will collapse in time due to weight and gravity. Leaves column of rock not attached to the cliff known as a stack. Continued erosion and weathering lead to formation of a stump that's visible only at low tide. |
| Longshore drift | Movement of sand pebbles down a coastline. Direction of the waves hitting coastline determined by direction of prevailing winds (swash). Wave always return to the sea in a straight line at 90 to coast (backwash). Water being pulled by gravity will take the shortest route back to beach. Such material moved along beach until obstruction found. Creates landforms on a coastline such as spits and bars. Also problem in river estuaries due to the deposition of sediment. Some used to harbour boats, constantly dredged because of longshore drift deposting material. |
| Beaches | Most easily recognsible feature around the British coast. Area of land between the low tide and storm tide marks and is made of sand, pebbles and in some cases mud and silt. Formed by constructive waves, often in bays as waves have less energy so deposit material. Can also be found along straight streches of coatline where longshore dirft occurs. Seaside resorts often build groynes to keep beaches in place and reduce effects of longshore drift. |
| Spits | Long narrow strech of pebbles and sand attached to the land at one end with the other end tapering into the sea. Forms when longshore drift occurs on a coastline and it ends sea deposits the transported material due to change in depth, deeper, so unable to further transport material. If there's a river etuary, then the meeting of the waves and river causes change in speed both drop sediment. Overtime material builds to form ridge of shingle and sand: spit. On land side silt and alluvium are deposited and salt marshes form. Wind and sea currents may curve end of the spit around. Dynamic as ever-changing. Hooks may also form due to secondary wind. If spits present can determine direction of long shore drift. |
| Bars and Tombolo | When spit develops in a bay builds across linking two headlands. Only possible if there is a gently sloping beach and nor river entering the sea. Such bars can straighten coastlines. Example is Slapton Ley in Devon which also has lagoon formed behind the bar where any run off water is trapped and slowly seeps through the bar to the sea. Tombolo just when spit connects to island creating a link. |
| Factors affecting rate of coastline recession | more gentle the beach more energy will lose, more resistant rocks like granite erode more slowly than less resistant rocks like clay. Rocks well jointed or with many faults like limestone erode more quickly as waves exploits weakness. Cliffs that are gentle and well vegetated will be more resistant to mass movement and weathering than cliffs of bare rock as well as rate of erosion by sea. |
| Coastal recession on the North Norfolk coas | coasts new Shoreline Management Plan which adapts a managed retreat rather than hold the line policy will mean nearly 1000 homes, 1400 caravan and chalet parks, 6 hotels, 7 golf courses, 7 historic buildings, 3.5km of road and 3 community halls will be lost to the sea over the next 100 years. Government saves 41 million pounds estimated economic cost is 100 million pounds with 357 million pounds lost in tourism. Sheringham golf course is now to its fifth and sixth holes. |
| Happisburgh | Population of 850 one of fastest eroding areas in the world. Area was defended in 1958 with revetments reducing the amount of erosion to about 50 cm a year. 1995 council stopped revetments coastal erosion rised. Since 25 properties and villages lifeboat launching station have been washed away. Main concern beach road which terminates in the seahouses were once worth 80000 pounds now 1 pound. Governments no protect as not cost effective. Less valuable than cost of defences to protect it even though contains 18 listed buildings including grade 1 listed church only 60m from cliffand estimated to be in sea from 2020. Cost of sea defences approximately 4 million for 500 metres. Although distric council did defend area in 207 with 5000 tonnes of granite rip rap cost of 200,000 local villagers raised further 40,000 on website brought another 1000 tonnes of rock. |
| Walton-on-the-Naze Location | Location: Coastal town in Essex Type of Country: Coastal town (HIC)- High Income Country Location of Walton on the Naze and name of important regions Situated close to London Located in Colchester Also situated close by is the Hamford Water National Nature Reserve Two distinct regions: North and South North not protected not cost effective South protected due to town and pop of 12,000. |
| Walton on the Naze causes of coastal recession | As a result of the types of rock that make up the cliff; London Clay and Red Crag which are both rock types that are easily eroded by the sea The bottom layer of the cliff is made of london clay which is impermeable, middle layer Red Crag is permeable as is made of silt and sand, the top layer is wind blown sand therefore the top two layers allow water to soak through such that slumping can occur as the cliff is less stable Cliffs suffer from slumping which makes the defence of area even more difficult The area has a long fetch so waves have greater energy to erode Longshore drift moves sand along the coastline from south to north. |
| Walton on the Naze potential impact | Coastal town of Walton has a population of 12,000 Grade 2 listed tower Several houses on Old Hall Lane Coastal properties Loss of habitat for wildlife Properties on the cliff like Sunny Point road where average house price is 400,000 pounds |
| Walton on the Naze management strategies used | Seawall At the bottom of the cliff there is a seawall to protect the London Clay which is easily eroded by the sea Breakwaters Groynes Usually made of wood stretches from the sea coastline into the sea Built to stop longshore drift movement from south to north Beach replenishment In 1999 beach replenished with sand and gravel from Harwich harbour Rip-rap Cliff regraded Also drainage channels installed to produce a gentle stable slope protecting properties Pier Drainage channels Afforestation Slope planted with gorse and nettles to stop people climbing on the cliff 1998 300 tonnes of Leicester granite placed around tower |
| Hard engineering: Rip rap | large rocks placed in front of cliff costs 300 per metre. Dissipates wave energy, very cheap: dependant on rock type, effective for many years (long term) Can make the beach inaccessible for tourists (economic), aesthetically displeasing, not effective in storm conditions |
| Hard engineering: Recurved seawall | Walls usually made of concrete. Modern used a recurved surface more effective. Costs 3,000 per linear metre Reflects and absorbs wave energy, very visible so makes residents feel safe, long term (effective for many years) Aesthetically displeasing- off putting for tourists (economic decline), expensive to build, can cause wave scouring if not properly positioned (marks on sea wall). |
| Hard engineering: Groynes | Usually mad of wood are stretches from coastline form sea costs 5000 pounds. Prevents longshore drift sand builds up on one side of the groyne, keeps beach in place for tourist industry (economic +), long term (effective for bla bla bla we know) Aesthetically displeasing they all are- difficult to walk across beach, disrupt natural process working on beach like Long shore drift |
| Hard engineering: Gabions | Wire cages filled with stones used to reduce erosion costs 11 pounds per metre Cheap so cost effective, rock cages absorb wave energy Wire cages may break: must be securely tied down, not as efficient as other forms of coastal defence. |
| Hard engineering: Offshore reef | These are enormous concrete block and natural boulders sunk offshore to alter wave direction and to dissipate the energy of waves and tides by wave refraction- costs 1950 pounds per metre. Waves break further offshore hence reduce erosive power, allow build up of sand due to the reduction in wave energy May be removed by heavy storms, difficult to install the reefs |
| Soft engineering: Beach replenishment | Placing of sand and pebbles on a beach- costs 5000 pounds per 100 metres Looks natural (aesthetically displeasing), provides beach for tourists (economic), beach best form of natural defence as dissipates wave energy (wave refraction), cheap. may affect wildlife: plant and animal life Scheme requires constant maintenace: can be washed away in as little as one year. Disruptions for home owners; large noisy lorries full of sand regularly replenishing the beach. |
| Soft engineering: Cliff regrading | Cliff is cut back and given a new gentle slope to stop it slumping Can be cover in ecomatting to encourage vegetation growth, aesthetically pleasing (looks natural) - will encourage wildlife in the area Not effective alone requires other defences at foot of cliff, somes homes on the cliff may have to be demolished. |
| Soft engineering: Managed retreat | Allowing the sea to gradually flood land or erode cliffs cost is dependant on coastal area Creates new habitat for plants and birds, cheap so cost effective Upsetting for landowner lose land, difficult to estimate extent of sea movement especially with rising sea levels. |
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