OCR A Level Geography Coasts Exam Study Guide., Exams of Geography

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Aspects of a coast system Inputs; Outputs; Processes/Fluxes. They can be open or closed, depending on the scale. Components of coastal system Flux Reservoir/store Residence Time Positive/Negative feedback Limit/threshold Tipping point Terrestrial system name Lithosphere Marine system name Hydrosphere store definition How much energy/material and where flux definition Rate of flow between stores Process Definition Physical mechanisms driving flux Examples of inputs in coastal systems (local) Precipitation; waves; wind; animals; human actions; geological material; ocean sediment; coastal defences; hydraulic action Examples of coastal processes Material traction (Longshore Drift); life cycle of animals and plants (synoptic link to ELSS); weathering; erosion Coastal processes outputs Sediment movement; destructive waves; evapotranspiration; human activity Examples of coastal stores All coastal landforms are stores Aeolian definition Wind related Equilibrium Positive feedback for cave formation example Small crack forms in headland Erosion causes the crack to expand into the cliff This eventually becomes large enough to be a cave Which leads to arches, stacks and stumps Negative feedback loop dunes example Storm waves erode a dune Material deposited offshore as a bar Wave energy is reduced due to effects of bar Less erosion Dune is replenished by constructive waves Positive feedback loop groynes example Groynes constructed Beach starved of sediment downdrift of groynes More erosion to beach as less energy is dissipated by large beach This depletes other nearby stores Which starves more sediment Non-linear change Magnitude of response in relation to the magnitude of the input Main sources of marine sediment Seabed Beach (destructive waves) Cliff face (erosion/weathering) Terrestrial landforms (via fluvial and aeolian processes) How is sediment transported? Solution, suspension, saltation and traction LSD Aeolian Human activity Sediment cell A length of coastline which is relatively self contained in terms of movement of sediment (there are 11 around England and Wales). Sediment sub-cell A division of a sediment cell based on best available knowledge of large-scale processes within that cell Characteristics of a sediment cell Overall balance of erosion and deposition Clear boundaries (high energy required to mave between them, which isn't available under normal conditions) Systems are theoretically closed Sub cells exist within them Water and wind currents taken into account when designating Adur and Arun rivers Dredging in SD - how much and where? 320,000m‘3 at Shoreham Harbour 5000m’3 at Brighton Marina 5000m*3 at Newhaven Harbour Impact of coastal defences on sediment cell Sediment is pushed offshore as breakwaters are surpassed Beachy Head loses 5000m‘3 of sediment per year to the beaches at Eastbourne The gravel store at Birling Gap is being depleted, with the sediment being deposited south of Pagham Harbour 8/22km of cliffs are physically protected, which reduces the quantity of flint sediment entering the cell Rottingdean, Saltdean and Seaford beaches are significantly depleted How are waves formed? Wind blows over the surface of the water, creating drag and gaining grip, with the friction causing disturbance and forming waves as a result Types of waves Local: steeper, smoother, shorter-period and higher energy. Formed by local winds Swell: shallower, longer period and lower energy. Formed by storm winds from hundreds or thousands of miles away. What aspects of wind affect waves Velocity; duration; fetch (distance) Distribution of energy within waves Potential energy at top; kinetic energy within base Why do waves break? Friction at the base causes the bottom of the wave to move slower than the top, until it collapses. Changes to waves as they get closer to the shore Wavelength decreases, as they slow down Wave height increases, as the top gains more energy than the base How water moves within a wave Molecule starts in trough -> molecule rises up front of wave, and is also dragged slightly forward -> molecule hits peak -> molecule slides down rear of wave back into the next trough Parts of a wave Wavelength: trough to trough/peak to peak distance Stillwater level Crest length region: part above Stillwater Trough length region: part below Stillwater Depth: distance from Stillwater to floor They break as spilling waves and the strong swash goes far up the beach As the frequency is low, backwash returns to the sea before the next wave, so swash is uninterrupted and remains high energy ition and characteristics Destructive waves defi Wave that has a net removal of sediment i.e. backwash is more energetic than swash Higher, shorter and more frequent (12-14 per min) Tend to be plunging, so little forward transfer of energy Friction fram the steep beach slows the swash so it doesn't travel far The next waves swash is slowed by the previous wave's backwash Zones of waves (moving towards land) Breaker zone: where the orbital motion of a wave becomes more elliptical as it gets closer to the sea bed. Longshore bars often below. Surf zone: low flat waves start to spill over here. Swash zone: the zone between breaking and the high water mark, where swash pushes up the beach. Backshore: the region of the beach usually untouched by waves, except in storm conditions Berm A nearly horizontal accumulation of sediment parallel to shore; marks the normal limit of sand deposition by wave action. Tide, definition. The term used to describe the rise and fall of ocean water levels, due to the gravitational influence of the moon and sun Period of a full tidal cycle 12 hours 25 minutes Spring tide vs neap tide Spring: when moon is between earth and sun - the highest tidal range of the lunar cycle. Occur shortly after New and Full moons. Neap: smallest tidal range when the moon, earth and sun form a right angle. Occur after first and third quarters. Twin bulges When the earth is between the sun and moon How do tides affect the coastal landscape? In restricted seas (such as the Med), tidal ranges are low, so variation in wave action is restricted. In places where the coast is funnelled (such as the Severn Estuary or Gibraltar), tidal ranges can be up to 14m. Tidal range influences where wave action occurs, the weathering processes that occur on land caught between high and low tide, and the potential scouring effects of waves. 3 main components of beaches Nearshore: where the seabed influences the waves Foreshore: the surf zone Backshore: the part of the beach above the usual reach of the waves Offshore and subtidal zone Depth is more than 1/2 the wavelength, and there is limited sediment movement Zone in which all coastal landforms are formed Intertidal Zone - between spring high and low tides Orthagonals Lines drawn at right angles to the crest of a wave, to create an image of wavefronts wave refraction the bending of waves so that they move nearly parallel to the shoreline Impact of wave refraction on waves Reduces speed Changes shape of waves, as they hit the shallow sea bed at different times due to differing coastal geography What happens if refraction is completed? Wave fronts will be parallel to the shore. Wave energy will be evenly distributed. Impact of wave refraction on an irregular coastline Destructive/erosive activity is concentrated on the headland as the water is shallower around here, as the waves refract and converge on the headland. Lower energy waves converge in bays, as the waves align with the shoreline, leading to higher rates of deposition. These phenomena cause headlands and bays to converge. attrition Rocks and pebbles crash into each other within the waves, becoming smaller, smoother and rounder. Abrasion Rocks and pebbles scraping along the surface of the rock, beach or cliffs Hydraulic pressure The force of water pushing air into cracks Solution Chemical reactions in the water dissolve the rocks (such as sulphuric acid and calcium carbonate) Wave pounding The force of the waves against beaches and cliffs Traction Boulders and pebbles being rolled along the river bed at times of high discharge The velocity at which particles are deposited Settling velocity relation to size Larger particles have higher settling velocity, so as energy decreases, larger particles are deposited first. What causes water to slow down and deposit material? Friction fram the seabed/coastal defences. The rate of accumulation exceeds the rate of deposition. At the top of swash, water slows to a stop. Some water percolates into the beach during backwash. Lithology What rocks are composed of (chemical) rock structure The properties of individual rocks (joining, bedding, faulting) What influences hardness of coastal rock? Heating and compression during formation makes igneous and metamorphic rock more resistant. Sedimentary rocks are generally softer and easier to erode - this means cliffs in the SE erode between 3- 6m per year. Why are higher cliffs harder to erode? Slumping means that the base gains more replenishment. How can permeability influence cliffs? Occurs as a result of the incidence of pores, or as a result of fissures, cracks and joints. Surface water seeps into cliffs, which can increase resistance (chalk cliffs in the UK are significantly influenced by rain seeping in). How can physical makeup influence cliffs? The amount of joints, bedding planes and faults can impact the rate of weathering. It can also dictate how strong the cliff is, and therefore exacerbate the effect of subaerial and marine erosion. Faults are exploited to make bays and headlands. How can chemical composition influence cliffs? Silica-based rocks are inert so erode very slowly. Iron compounds oxidise and break down, weakening the cliff. Rocks with feldspar are changed into clay minerals by hydrolysis, weakening them. Limestone is decomposed by carbonation, causing wave-cut platforms to disintegrate more quickly. Basalt weathers 14x quicker under salt water conditions. Slide definition Where a large mass of material moves on a cliff, but retains its internal structure. slump definition thermal expansion rocks expand and contract when heated and cooled. Frequent variations in temperature cause "onion skin layering", which can be exacerbated by the presence of water. Salt crystallisation saline solutions go into porous rocks, which then form crystals as the water evaporates, which cause stress and disintegrates the rock. Sodium-based salts expand up to 300% in temperatures 26-28”. Examples of chemical subaerial weathering Oxidation Carbonation Solution Hydrolysis Hydration Oxidation Some minerals react with oxygen (particularly iron). The oxide becomes soluble in acidic conditions. Example is iron in sandstone. Carbonation Carbonic acid in rain reacts with calcium carbonate to produce a soluble substance, which is dissolved. This reaction is reversible, so water can leave behind deposits in the form of stalagmites and stalactites. Solution (subaerial weathering) Some salts are soluble, causing rocks with these salts in to be dissolved in rain. Other substances can be dissolved by acid in rain/seawater. Hydrolysis Chemical reaction between minerals in rock, and water. Silicates combine with water and produce secondary minerals (such as clay). Hydration Water molecules added to molecules in rocks to make larger-molecule minerals, which can cause surface flaking, as the minerals expand in volume. Examples of biological subaerial weathering Tree roots Organic acids Tree roots impact on subaerial weathering Grow into cracks/joints and exert outward pressure (similar to freeze thaw). When trees topple, their roots exert leverage on rocks and soil, bringing them to the surface. Organic acids impact on subaerial weathering Decomposition of organic material produces acids, which react with minerals (chelation). Blue green algae produce acids that create iron and manganese oxide. Molluscs secrete acid.