Backwash
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The distance a wave has travelled.
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Waves are caused by the transfer of energy from the wind to the sea due to the friction of the wind on the water’s surface.
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Swash
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Weak swash, strong backwash.
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The wearing away of land by the sea.
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Coastal erosion is the wearing away of the land by the sea.
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Waves hitting the base of a cliff causes leads to air compression in cracks, joints and folds in bedding planes, causing repeated changes in air pressure. As air rushes out of the crack when the wave retreats, it leads to an explosive effect as pressure is released. This process is supported further by the weakening effect of weathering. The material breaks off cliffs, sometimes in huge chunks. This process is known as hydraulic action.
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Corrasion is when destructive waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff. Over time this can loosen cliff material forming a wave-cut notch.
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Corrasion, abrasion, hydraulic action, attrition and corrosion/solution.
Find out more about the processes of coastal erosion.
Mechanical weathering is the breakdown of rock without changing its chemical structure (composition).
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Weathering is the breakdown of rock in situ by the action of rainwater, extremes of temperature, and biological activity.
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When rainwater hits rock it decomposes it or eats it away. This is known as carbonation. This occurs when slightly acidic (carbonic) rain or seawater comes into contact with sedimentary rock, such as limestone or chalk, it causes it to dissolve. A chemical reaction occurs between the acidic water and the calcium carbonate and forms calcium bicarbonate. This is soluble and is carried away in solution. Carbonation weathering occurs in warm, wet conditions.
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Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through). Water enters the rock and freezes. The ice expands by around 9%. This causes pressure on the rock until it cracks. Repeated freeze-thaw can cause the rock to break up.
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Recently weathered rock can be seen at the foot of chalk and limestone cliffs and is easily identified because it is angular.
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Longshore drift happens when waves approach the beach at an angle. The swash (waves moving up the beach) carries material up and along the beach. The backwash (waves moving back down the beach) carries material back down the beach at right angles. This is the result of gravity. This process slowly moves material along the beach and provides a link between erosion and deposition. The material is transported through suspension, traction, solution and saltation. Longshore drift provides a link between erosion, transportation and deposition.
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Longshore drift
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The movement of sediment and beach material through wave action.
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Coastal transportation involves material being transported by the sea being deposited or dropped.
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Solution, suspension, saltation and traction.
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