3 e coasts (1)
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3 e coasts (1) Document Transcript

  • 1. CoastsA coast is found where the land meets the sea. Coasts are constantly shaped by the sea, air and the action ofwaves. Waves act in different ways, through the processes of erosion, transportation and deposition.Each of these processes involves the power of the sea and the effect of waves that are carried to shore.However, other factors also change and shape our coasts:Human Activity and Land useThe way in which humans manage and use coastal areas helps shape the coast. Some areas of coast arevalued more than others. This will influence the way coasts are used and managed.Weather and ClimateThe weather and climate of coastal areas can contribute to the process of erosion and weathering.GeologyThe geology and rock types found in coastal areas influence how coastal processes work ie hard rock resistserosion.WavesThe power of waves is one of the most significant forces of coastal change. Waves are created by windblowing over the surface of the sea. As the wind blows over the surface of the sea, friction is created -producing a swell in the water. The energy of the wind causes water particles to rotate inside the swell. Thismoves the wave forward.The size and energy of a wave is influenced by:• the length of time that the wind has been blowing• the strength of the wind• how far the wave has travelled (called the fetch)Destructive waves• operate in storm conditions• are created from big, strong waves when the wind is strong and has been blowing for a long time• occur when wave energy is high and the wave has travelled for a long time• tend to remove material from the coast and associated with erosion• backwash is stronger than the swashConstructive waves• operate in calm weather• are less powerful waves• break on the shore and tend to deposit material, building up beaches• are responsible for transporting material• swash is stronger than the backwashWhen a wave breaks, water is washed up the beach: this is called the swash. Then the water runs back downthe beach: this is called the backwash. With a constructive wave, the swash is stronger than the backwash.With a destructive wave, the backwash is stronger than the swash.ErosionThe sea changes and shapes the coastal landscape. Erosion is the wearing away and breaking up of rock andbeach material found along the coast. Destructive waves will erode the coastline in the following four ways.• The constant force of waves crashing on the shore damages it. This is called hydraulic action.• Waves bring with them bits of rock and sand. These help to grind down cliffs. This is called abrasion.• Waves cause rocks and pebbles on the shore to smash into each other and break down. This is calledattrition.• Acids contained in sea water will slowly dissolve certain types of rock. This is called corrosion or solution.Transportation and depositionWaves tend to approach the coast at an angle; this is because of the direction of the prevailing wind. Thiscauses the waves to break on the beach at an angle. The swash of the waves carries material up the beach atan angle. The backwash then flows back to the sea in a straight line. This movement of material is calledtransportation.On many coasts the combined effect of continually repeating swash and backwash is to transport materialsideways along the coast. This movement of material along coasts is called longshore drift.DepositionWhen the sea loses energy, it drops its load of sand, rock particles and pebbles, that it has been carrying. This iscalled deposition. Deposition happens when the swash is stronger than the backwash.Deposition is likely to occur when:• waves enter an area of shallow water• waves enter a sheltered area• there is little wind
  • 2. Coastal features are caused either by the processes of erosion (the wearing away of rocks) or deposition(movement of eroded material by the sea to a new location).Coastal features created by erosionAlong a coastline there are often many features created by erosion. The most common of these are:cliffs headlands bays caves arches stacksCliffsOne of the most common features of the coastline in Britain and around the world are cliffs. Cliffs are shapedthrough a combination of erosion and weathering. The weather attacks the cliff top. The waves attack the clifffoot, 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 andcreates steep cliffs.Headlands and baysAnother group of features shaped by erosion are headlands and bays. Headlands are formed when the seaattacks 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, suchas chalk. This leaves a section of land heading out into the sea; this is called a headland. The areas where thesoft rock has eroded away, next to the headland, are called bays.Caves, arches and stacksErosion can create caves, arches and stacks along a headland. Again weathering can also help to createthese landforms. Caves occur when the waves force their way into cracks in the cliff face. The water containssand and other materials that help to grind away at the rock until the cracks become a cave. If the cave isformed in a headland, it may eventually break through forming an arch. The arch will gradually becomebigger and bigger until it can no longer support the top of the arch. When the arch collapses, it leaves theheadland on one side and a stack (a tall column of rock) on the other.Coastal features created by depositionAlong a coastline you can find features created by deposition. These include:beaches spits bars sand dunesBeachesBeaches are one of the most common features of a coastline. Beaches are made up of eroded material thathas been transported from elsewhere and deposited here by the sea. Constructive waves help to build upbeaches. The type of material found on a beach ie sand or shingle) is influenced by the geology of the areaand wave energy.SpitsSpits are also created through the process of deposition. A spit is an extended stretch of beach material thatprojects out to sea and is joined to the mainland at one end. Spits are commonly formed where there is aprevailing wind and where there is a longshore drift.BarsA bar is a long stretch of beach material (sand or shingle) that joins together two headlands. A lagoon usuallyforms behind the bar.Sand dunesA sand dune is a small hill of sand found at the top of a beach. The waves do not usually reach this area of thebeach. Vegetation may be found on sand dunes and such areas can be important ecosystems.FiordIn valleys created by glaciers. They are very deep.RiasIn valleys formed by rivers. They are more winding with low, gentle sides.Physical management of the coastPhysical management of the coast is concerned with natural processes such as erosion and longshore drift.Management techniques fall into two categories: hard engineering and soft engineering.Hard engineering - options tend to be expensive and short-term options. They may also have a high impact onthe landscape or environment (wooden croynes, concrete walls, artividial breakwaters).Soft engineering - options are often less expensive than hard engineering options. They are usually also morelong-term and sustainable, with less impact on the environment.Beach nourishment - this replaces beach or cliff material that has been removed by erosion or longshoredrift.The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beachesalso attract tourists.While it can be a relatively inexpensive option it requires constant maintenance to keepreplacing the beach material as it is washed away.Managed retreat - this is where areas of the coast are allowed to erode and flood naturally. Usually this will beareas considered to be low value.The advantages are that it encourages the development of beaches (anatural defence) and salt marshes (important for the environment) and cost is low.While this is a cheap option,it will not be free as people will need to be compensated for loss of buildings and farmland.