Coastal Landscapes in the UK

• Weathering describes the natural processes that break down rocks. There are 3 main types of weathering - mechanical weathering, chemical weathering, and biological weathering.
• Mechanical weathering

  • The chemical composition of rock stays the same in mechanical weathering (also called physical weathering).
  • The main type of mechanical weathering that affects coastlines is freeze-thaw weathering. This happens in colder weather conditions when water fills a crack in a rock and freezes.
  • Water expands when it freezes causing the crack to get wider and deeper.
  • When the ice melts, there is now a larger crack that fills with water and then freezes again.
  • This process of freezing and melting (known as thawing) can cause significant erosion on coastlines over time.
• Chemical weathering

  • In chemical weathering, the chemical composition of rock changes.
  • When the climate is warm and wet, carbonic dioxide can dissolve in rain to create a 'carbonic acid'.
  • The carbonic acid in rainfall hits rocks and dissolves the parts of the rock made of calcium carbonate.
  • This also breaks down rock.
• Biological weathering

  • In biological weathering, living things (organisms) break down rock.
  • Plant roots can biologically weather a rock by pushing cracks apart.
• Mass movement describes the large movement of soil and rock down the slope of a hill or cliff.
• What causes mass movements?

  • Mass movements are caused by weathering, erosion, and gravity.
  • Small changes over time can mean that the centre of gravity of a cliff can hang over the sea, instead of over land making the cliff unstable and prone to mass movement.
• Rockfalls:

  • Rockfalls are when the cliff (materials) break and crumble down the cliff.
• Slides:

  • Slides are when material moves down a slope in a straight line.
• Slumps:

  • Slumps are when material moves down a slope at a curve.
• What are constructive waves?

  • Constructive waves are not very tall.
  • When the sea's waves are constructive, we say that the sea is calm.
  • Constructive waves have a longer wavelength than destructive waves which means individual waves are spread quite far apart.
  • Constructive waves have a low frequency (about 7-10 waves arrive at the beach each minute).
  • Constructive waves deposit material onto coastlines because they have strong swash and weak backwash. This means that more material is deposited onto the beach than the weak backwash can drag material away.
• What are destructive waves?

  • Destructive waves are taller and more frequent than constructive waves.
  • Destructive waves have a high frequency. They have around 10-15 waves per minute.
  • Destructive waves cause most of the erosion of coastlines.
  • Destructive waves have a stronger backwash than swash, meaning they drag more material away from the coastline than is deposited on the shore.
• What is deposition?

  • Deposition describes the sea putting (depositing) solid material from the sea onto the land on the coastline.
  • Constructive waves deposit material on coastlines because their swash depositing things on the beach is stronger than their backwash dragging things from the beach.
• How do destructive waves erode the coast?

  • Destructive waves erode the coast using 3 erosional processes:
  • Hydraulic power: The force of wave actually breaks the rock itself.
  • Abrasion: The material and rock being carried by the sea damages the coastal rock.
  • Attrition: The bedload collides with itself, eroding it.
• Type of rock

  • Headlands and bays are formed in areas that have alternate areas of hard and soft rock facing the sea.
  • Rock with lots of cracks and joints is called soft rock.
  • When the sea hits both the soft and hard rock, more of the soft rock is eroded.
  • Amongst soft rocks, talc is the softest rock.
  • Clay is a softer rock than chalk, so erodes more quickly.
  • Among hard rocks, sandstone is harder than limestone.
• Joints and faults

  • Rocks that have lots of cracks, faults or joints are softer than rocks with fewer cracks and weaknesses.
  • Soft rocks with lots of joints & faults will be eroded more quickly.
• Concordant coastlines

  • Concordant coastlines have a layer of soft rock, then a layer of harder rock, then a layer of soft rock next to each other.
  • This diagram shows a sand dune on top of a concordant coastline.
  • The sea's waves will only hit 1 type of rock when they meet the coast.
• Discordant coastlines

  • Discordant coastlines have alternating chunks of hard rock and soft rock at 90o to the coast. The sea's waves will hit both hard rock and soft rock when they meet the coast.
  • Bays are usually created where the sea meets the areas of soft rock and headlands are created where the areas of hard rock are.
• Seasonality

  • Temperature changes and the range of temperatures that rock is exposed to can affect erosion and weathering.
  • Water expands when it freezes. When water fills cracks in rocks, if it then freezes, it expands, putting pressure on the rock. The water will then melt, but it has put pressure on the rock. Eventually, this process of freezing and thawing will wear down rock. This is called freeze-thaw weathering.
• Rainfall

  • At times of heavy rainfall, soil can become saturated, and mass movements may be more likely.
  • After heavy storms, chemical weathering may be more likely to happen.
  • Heavy rainfall is often accompanied by storms and destructive waves.
• Storm frequency

  • Many parts of the UK are frequently hit by storms.
  • If storms happened more often, then erosion and weathering would happen more quickly.
• Prevailing winds and wind speed

  • The prevailing winds affect where sediment is carried.
  • Strong prevailing winds can lead to lots of destructive waves.
  • Winds from the Atlantic Ocean hit the south-west of England.
• Wavecut Platforms - Stage 1

  • Destructive waves are responsible for most of the erosion at the base of cliffs.
  • Hydraulic action and abrasion wear away the base of the cliff around the high tide mark.
  • Eventually, this erosion causes a wave-cut notch to form.
• Wavecut Platforms - Stage 2

  • Continued erosion of the wave-cut notch causes the rock above it to become less and less stable until it collapses.
• Wavecut Platforms - Stage 3

  • Waves wash away the debris from the cliff collapse.
  • The destructive waves begin to erode the cliff, causing a new wave-cut notch to form.
• Wavecut Platforms - Stage 4

  • As stages 1-3 happen again and again, more debris falls into the ocean and the cliff retreats.
  • What is left behind is called a wave-cut platform.
  • A wave-cut platform is a flat, gently sloping ledge of rock that extends out into the sea from the base of the cliff.
• Rock with lots of cracks and joints is called soft rock. Headlands are made of resistant rocks with not many weaknesses. As headlands are eroded, these landforms can be created:

  • Caves
  • Arches
  • Stacks
• Caves

  • There are cracks, joints, and weaknesses in rocks.
  • When cracks get wider (because of hydraulic action, abrasion or attrition), they can become large enough to create a cave.
• Arches

  • Caves can be eroded from one side of the rock through the other.
  • This creates an arch.
  • You can see right through an arch to the other side of the rock.
  • Durdle Door (Dorset), Bow Fiddle Rock (Scotland), and the Green Bridge of Wales (Pembrokeshire) are the 3 most famous arches in the UK.
• Stacks

  • When the top of an arch collapses because of gravity, a column called a stack is left behind.
• Coastal deposition describes the sea dropping sediment (or material) being carried by the water at the coastline. Coasts grow in size when more sediment is deposited on the coast than is lost to the process of erosion.
• Why does deposition happen?

  • Deposition happens when constructive waves break on the shore. The sediment being carried by the sea is put (deposited) on the coastline.
  • This usually creates beaches made of sand or shingle in the area between the 'high' water mark and the 'low' water mark.
  • The high water mark is the point the highest up the beach that the sea level rises to.
  • The low water mark is the point the lowest down the beach that the sea level falls to.
• What increases the amount of deposition?

  • If erosion on the nearby coast is high, then lots of rock and sand will fall into the ocean. This will increase deposition on nearby beaches.
  • The more sediment in the ocean, the more deposition there will be.
• Why are some beaches sandy & some shingle?

  • Sandy beaches are created by sand being deposited on the shoreline.
  • Sandy beaches are usually very long, wide, and flat because particles of sand are very small and easy to wash back into the ocean with the backwash.
  • Shingle beaches are made when pebbles and shingle are deposited on the coast. Shingle and pebbles are big and hard to wash back into the ocean, so they build up (making short and steep beaches).
• Spits

  • Spits are piles of sand that create sheltered zones on the coast.
  • When the coast changes direction at an estuary (where a river meets the sea), longshore drift continues to move sediment across the inlet.
  • The river doesn't let the longshore drift completely join to the coast on the other side because the river has the energy to move the sediment.
  • Spits are the long fingers of sand sticking out from one side on a coastline. They often have marshland forming in the sheltered zone.
• Bars

  • A bar is created when a spit grows across a bay.
  • Lagoons (saltwater pool separated from the ocean) are often created behind a bar.
• Sand dunes

  • Sand dunes are hills of sand created at the back of a beach.
  • The wind blows deposited sand up the beach. Objects like wood, driftwood or human rubbish can block the wind, leading to hills of sand.
  • The hills of sand can allow plants and vegetation to grow.
  • This leads to more sand building up.
  • Older sand dunes (hills) are called mature dunes.
  • Newer sand dunes are called embryo dunes.
• Human activities affect coasts both directly and indirectly. Direct effects are immediate consequences of human's behaviour. Indirect effects happen as a knock-on effect of the primary effects.
• Development

  • If lots of people live in coastal towns, they will have lots of houses, businesses and railway lines that will need protecting from floods, erosion, and weathering.
  • Indirectly, areas away from towns are more likely to be harmed. Towns can be protected by sea walls, groynes or other defences. However, as with the Holderness Coast, sometimes this can just shift the impact of erosion further down the coast.
• Agriculture

  • Agricultural land is less valuable than land that has housing, businesses or infrastructure on it.
  • Farmland could be lost as coastal erosion destroys land.
• Industry

  • Most industries do not locate right next to the coast.
  • The Fukushima disaster in Japan happened when a coastal nuclear power station was damaged in a tsunami.