Coasts

• Wave


  Crest, trough, wavelength, and wave height
• Wave formation


  1. Winds move across the surface of the water, causing frictional drag which creates small ripples and waves

  2. As the seabed becomes shallower towards the coastline, the orbit of the water particles becomes more elliptical, leading to more horizontal movement of the waves

  3. Wave height increases, but wavelength and wave velocity both decrease

  4. Water backs up from behind the wave until the wave breaks and surges up the beach
• Factors influencing wave size and energy

  • Strength of the wind
  • Duration of the wind
  • Size of the fetch
• Swash


  The movement of the wave onto the beach after a wave breaks. Material being carried by waves is deposited onto the beach.
• Backwash


  The movement of the wave back down the beach. Backwash drags any material off a beach.
• Constructive waves


  Tend to deposit material, creating depositional landforms and increasing the size of beaches. Swash is stronger than backwash.
• Destructive waves


  Act to remove depositional landforms through erosion, decreasing the size of a beach. Backwash is stronger than swash.
• Characteristics of constructive and destructive waves

  • Constructive: Formed by weather systems in the open ocean, long wavelength, 6-9 waves per minute, low waves that surge up the beach
  • Destructive: Formed by localised storm events closer to the coast, short wavelength, 11-16 waves per minute, high waves that plunge onto the beach
• High-energy coastlines


  Associated with more powerful waves, rocky headlands and landforms, frequent destructive waves, erosion exceeds deposition
• Low-energy coastlines


  Have less powerful waves, sheltered areas with constructive waves, landforms of deposition as deposition exceeds erosion
• Wave refraction


  Waves turn and lose energy around a headland on uneven coastlines, wave energy is focussed on headlands creating erosive features, energy is dissipated in bays leading to lower energy environments like beaches
• Why waves break
• Processes of marine erosion

  • Hydraulic action
  • Corrasion
  • Abrasion
  • Solution
  • Attrition
• Hydraulic action


  As a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults within the rock. The high pressure causes the cracks to force apart and widen when the wave retreats and the air expands, fracturing the rock. Bubbles found within the water may implode under the high pressure creating tiny jets of water that erode the rock.
• Corrasion


  Sand and pebbles are picked up by the sea from an offshore sediment sink or temporal store and hurled against the cliffs at high tide, causing the cliffs to be eroded. The shape, size, weight and quantity of sediment picked up, as well as the wave speed, affects the erosive power of this process.
• Abrasion


  Sediment is moved along the shoreline, causing it to be worn down over time. The stones rubbing against things acts like sandpaper, wearing down materials over time.
• Solution


  The process of water dissolving rocks and material into solutions. The mildly acidic seawater can cause alkaline rock such as limestone to be eroded, similar to carbonation weathering.
• Attrition


  Wave action causes rocks and pebbles to hit against each other, wearing each other down and becoming round and smaller. Attrition is an erosive process within the coastal environment, but has little to no effect on erosion of the coastline itself.
• Types of weathering


  • Mechanical (physical) weathering
  • Chemical weathering
  • Biological weathering
• Mechanical (physical) weathering


  The breakdown of rocks due to exertion of physical forces without any chemical changes taking place. Includes freeze-thaw, salt crystallisation, and wetting and drying.
• Freeze-thaw (frost-shattering)


  Water enters cracks in rocks and then freezes overnight, expanding by around 10% in volume which increases the pressure acting on a rock, causing cracks to develop and the cliff to become more vulnerable to erosion.
• Salt crystallisation

  As seawater evaporates, salt is left behind. Salt crystals will grow over time, exerting pressure on the rock and forcing the cracks to widen. Salt can also corrode ferrous rock due to chemical reactions.
• Wetting and drying

  Rocks such as clay expand when wet and then contract again when they are drying. The frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up.
• Chemical weathering


  The breakdown of rocks through chemical reactions, including carbonation, oxidation, and solution.
• Carbonation


  Rainwater absorbs CO2 from the air to create a weak carbonic acid, which then reacts with calcium carbonate in rocks to form calcium bicarbonate, which can then be easily dissolved.
• Oxidation


  When minerals become exposed to the air through cracks and fissures, the mineral will become oxidised which will increase its volume, causing the rock to crumble.
• Biological weathering


  The breakdown of rocks by organic activity, including root action, bird burrowing, rock boring, seaweed acids, and decaying vegetation.
• Types of mass movement

  • Soil creep
  • Mudflows
  • Rockfall
  • Landslides and rockslides
• Soil creep


  The slowest but most continuous form of mass movement involving the movement of soil particles downhill. Particles rise and fall due to wetting and freezing, causing the soil to move down the slope, leading to the formation of shallow terracettes.
• Mudflows


  An increase in the water content of soil can reduce friction, leading to earth and mud to flow over underlying bedrock or slippery materials such as clay. Water can get trapped within the rock increasing pore water pressure, which forces rock particles apart and therefore weakens the slope. Mudflows represent a serious threat to life as they can be very fast flowing.
• Rockfall


  Occurs on sloped cliffs (over 40 degrees) when exposed to mechanical weathering, though mostly occurs on vertical cliff faces and can be triggered by earthquakes. It leads to scree (rock fragments) building up at the base of the slope.
• Landslides and rockslides


  Heavy rainfall leads to an increase in pore water pressure, which reduces the strength of the slope and can cause the slope to fail, leading to landslides and rockslides.
• Mudflows


  An increase in the water content of soil can reduce friction, leading to earth and mud to flow over underlying bedrock, or slippery materials such as clay
• Water


  Can get trapped within the rock increasing pore water pressure, which forces rock particles apart and therefore weakens the slope
• Mudflows represent a serious threat to life as they can be very fast flowing
• Rockfall


  Occurs on sloped cliffs (over 40°) when exposed to mechanical weathering, though mostly occurs on vertical cliff faces and can be triggered by earthquakes
• Rockfall leads to scree (rock fragments) building up at the base of the slope
• Landslides and Rockslides


  Heavy rainfall leads to water between joints and bedding planes in cliffs (which are parallel to the cliff face) which can reduce friction and lead to a landslide. It occurs when a block of intact rock moves down the cliff face very quickly along a flat slope
• Coastal transportation processes


  • Traction - Large, heavy sediment rolls along the sea bed pushed by currents
  • Saltation - Smaller sediment bounces along the sea bed, being pushed by currents
  • Suspension - Small sediment is carried within the flow of the water
  • Solution - Dissolved material is carried within the water, potentially in a chemical form
• Deposition


  Occurs when sediment becomes too heavy for the water to carry, or if the wave loses energy. Deposition tends to be a gradual and continuous process, so a wave won't release all its sediment at the same time