Coastal Landscapes (Edexcel GCSE Geography: B (1GB0))

• The coast can be defined as the meeting point between the land and sea
• Coastal processes are divided into two parts:
  • Marine processes: Offshore (water-based)
  • Terrestrial processes: Onshore (land-based)
• These processes are further divided into:
  • Wave action
  • Erosion
  • Transportation
  • Weathering
  • Mass movement
• Together with the local geology, these processes produce distinctive landforms around the coastline
• A coastline made up of softer rocks such as sands and clays will be easily eroded by destructive waves to form low, flat landscapes such as bays and beaches
• Coastlines of more resistant, harder rock will take longer to erode and produce rugged landscapes such as headlands
• Joints and faults expose rock to erosion and weathering
• The differences between hard and soft rocks will also impact the shape and characteristics of cliffs

The Effects of Rock Type on the Coastline

• Concordant coastlines are made up of the same rock type, running parallel to the sea, these coastlines produce coves 
• Discordant coastlines have alternating bands of rock perpendicular to the sea, these types of coastlines form headlands and bays
• Geology, therefore, shapes the coastline vertically through the height and profile of a cliff and horizontally with bays and headlands

Types of erosion

• Destructive waves are responsible for the majority of erosion that happens along a coast
• They cut into the coastline in four ways:
  • Hydraulic Action 
  • Attrition
  • Corrosion 
  • Abrasion 
• The effects of attrition are enhanced when the waves move sediment further and longer
  • A large, rough bolder is eventually eroded into round sand grains (quartz) the longer it stays in the water and the further it travels along the coast
• Rounded pebbles on a beach are known as a shingle

Headlands and bays

• Occur where there are alternating bands of hard and soft rocks run perpendicular to oncoming waves (discordant coastline)
• At first, the soft rock (e.g. clay) is eroded backward, forming an inlet
• As the inlet continues to erode it curves inwards, and a bay is formed, usually with a beach
• The hard rock (e.g. limestone) is left protruding out to sea as a headland

• A headland usually features:
  • Cliffs along its sides
  • Projects out to sea
  • Usually longer than it is wide
  • Geology is of resistant rock
• A bay usually has:
  • A wide, open entrance from the sea
  • A roughly, semi-circular shape extending into the coastline
  • Land that is lower than the headlands surrounding it
  • A bay may or may not have a beach

The formation of headlands and bays on discordant coastlines

Cliffs and wave-cut platforms

• Cliffs are shaped through erosion and weathering processes
• Soft rock erodes quickly and will form sloping cliff faces
• Steep cliffs are formed where there is hard rock facing the sea

• A wave-cut platform is a wide gently sloped surface found at the foot of a cliff:
  • As the sea attacks the base of a cliff between the high and low water mark, a wave-cut notch is formed
  • Abrasion, corrosion and hydraulic action further extend the notch back into the cliff
  • The undercutting of the cliff leads to instability and collapse of the cliff
  • The backwash of the waves, carries away the eroded material, leaving behind a wave-cut platform
  • The process repeats and the cliff continues to retreat, leading to a coastal retreat

The process of cliff retreat and wave-cut platform formation

Caves, arches, and stacks 

• These form in a headland because of wave action and sub-aerial weathering
• As waves approach the shore, their speed is reduced as they move along the sea floor
• This changes the angle of the waves, and they will turn so the crest becomes parallel to the coast - known as wave refraction
• This refraction concentrates erosive action on all sides of the headland
•  The erosional processes of hydraulic power, abrasion and some corrosion begin to attack any weaknesses in the headland
• As the crack begins to widen, abrasion will begin to wear away at the forming cave
• The cave will become larger and eventually breaks through the headland to form an arch
• The base of the arch continually becomes wider and thinner through erosion below and weathering from above
• Eventually, the roof of the arch collapses, leaving behind an isolated column of rock called a stack
• The stack is undercut at the base by wave action and sub-aerial weathering above, until it collapses to form a stump

The formation of a cave, arch, stack and stump

UK's overall climate

• The UK has a temperate maritime climate
• This means a mild, seasonal climate-cool, wet winters and warm wet summers
• Continentality, the North Atlantic Drift and air masses affect the UK weather
  • Continentality:
    • Coastal areas are warmer in winter and cooler in summer 
    • Seas take up the heat in the summer, cooling the surrounding land
    • During the winter, the heat is released, keeping the coastal land warmer
  • North Atlantic Drift:
    • Ocean currents bringing warm waters from the Caribbean to the west coast of the UK
    • This keeps the west coast of the UK warmer than other regions of the UK
  • Air Masses:
    
    • Large volumes of air with similar water content and temperatures
    • Classified by the region where they form: 
      • Arctic or Polar cold air
      • Tropical warm air
      • Maritime wet air
      • Continental dry air
• Five types of air masses that bring different weather to the UK:

The UK's Air Masses

Impact of UK climate on coastal erosion

• The UK's climate impacts coastal erosion in the following ways:
  • Th UK seasons affect the rate of weathering and erosion
    • Cold temperatures lead to freeze-thaw weathering on cliff faces, increasing rock falls
    • Winds are stronger in winter than in summer and stronger winds give energy to waves
  • Prevailing winds in the UK are from the south-west
    • This brings frequent rainfall and increases the rate of weathering
  • Storm frequency is high in many areas of the UK
    • Coasts are exposed to strong winds which increases destructive wave power 
    • Rainfall is heavily leading to flooding and increases in the mass movement

Wave action

• Waves are marine processes that erode, transport and deposit material
• Waves are formed as winds blow over the surface of the sea 
• The height and strength of a wave is dependent on 3 factors:
  • The fetch 
  • The amount of time the wind blows
  • The strength of the wind
• The greater the strength, time and fetch of the wind, the larger the wave
• As a wave enters the shallow water of the coast, friction from the seabed causes the wave to lean forward and eventually will crest and break onto the beach 
• The movement of water up the beach is called the swash, and the return movement is the backwash

• There are two types of waves:
  • Destructive waves erode the beach
    • They have a short wavelength, high-frequency rate and a steep wave gradient
    • Their backwash is stronger than their swash, which scours the beach, dragging material out to sea 
  • Constructive waves are beach builders
    • They have a long wavelength, low-frequency rate and a shallow wave gradient
    • The swash is stronger than its backwash, which carries material up onto the beach and deposits it there  

Comparison of Wave Type

Constructive waves are beach builders and destructive waves are the destroyers

• Weathering is best defined as:

The break-down of rock in-situ

• Weathering does not involve the movement of the material; this is what makes it different from erosion
• Sub-aerial weathering describes coastal processes that are not linked to the action of the sea
• It includes freeze-thaw weathering (mechanical) and chemical weathering
• Weathering weakens cliffs and makes them more vulnerable to erosion

• Mechanical weathering physically breaks up rock
  • Freeze-thaw or frost shattering is where:
    •  Water gets into cracks and joints in the rock
    •  When the water freezes it expands and the cracks open a little wider
    • When the water thaws, the crack contracts, releasing pressure on the crack
    •  Over time, repeated freezing and thawing, widens the crack until pieces of rock split off the rock face, whilst big boulders are broken into smaller rocks and gravel
• Chemical weathering occurs when rocks are broken down by a chemical process:
  • Rainwater is slightly acidic through absorbing carbon dioxide from the atmosphere
  • This reacts with minerals in the rock creating new material
  • Rock-type affects the rate of weathering e.g. limestone chemically weathers faster than granite
  • The warmer the temperature, the faster the chemical reaction
• Biological weathering takes place when rocks are worn away by living organisms:
  • Trees and other plants can grow within the cracks in a rock formation
    • As the roots grow bigger, they push open cracks in the rocks making them wider and deeper
    • Over time the growing tree eventually prizes the rock apart
  • Burrowing animals, such as rabbits, disturb the ground above the burrow, which puts pressure on any cracks, eventually leading to pieces falling off the rock

• Mass movement is:

The downhill movement of material under the influence of gravity

• Throughflow and runoff caused by heavy rain can also make cliffs more unstable and increase the likelihood of mass movement
• It includes landslides, slumping and rockfalls

• The type of movement is determined by:
  • Angle of slope (the steeper the slope the faster the movement)
  • Nature of regolith
  • Amount and type of vegetation
  • Water
  • Type and structure of rock
  • Human activity
  • Climate

• Soil Creep:
  • Common in humid climes with the movement of less than 1cm per year 
  • Soil expands when it freezes, gets wet or is heated up in the sun
  • As the soil expands, it lifts at right angles to the slope
  • When the soil shrinks, it falls straight back down
  • Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time

• Flow:
  • Occurs on slopes between 5° and 15° with speeds between 1 to 15km per year
  • Usually happens after the soil has become saturated with a flow of water across the surface
  • Vegetation is flattened and carried away with the soil

• Slide:
  • A movement of material 'en masse' which remains together until hitting the bottom of a slope

• Fall:
  • Slopes are steep and movement is rapid
  • Caused by a number of reasons:
    • Extreme weathering: Freeze-thaw action can loosen rocks that become unstable and collapse
    • Rainfall: Too much rain will soften the surface leading to the collapse of the slope
    • Earthquakes can dislodge unstable rocks 
    • Hot weather can dry out soil causing it to shrink and allowing rocks to fall

• Slump:
  • Usually found on weaker rock types (i.e. clay), that become saturated and heavy
  • This is common at the coast and is also known as rotational slip
  • It involves a large area of land moving down the slope in one piece
  • Because of the way it slumps, it leaves behind a curved indented surface

Major mass movement examples

• Material in the sea arrives from many sources:
  • Eroded from cliffs
  • Transported by longshore drift along the coastline
  • Brought inland from offshore by constructive waves
  • Carried to the coastline by a river
• Once in the water, the material is moved in different ways:
  • Traction 
  • Saltation
  • Suspension
  • Solution 

Longshore drift

• It is the main process of deposition and transportation along the coast 
• Influenced by the prevailing wind, waves approach the beach at an angle
• As the waves break, the swash carries material up the beach at the same angle
• As the swash dies away, the backwash carries the material down the beach at right angles (90°) 
• The process repeats, transporting material along the beach in a zig-zag movement

The process of longshore drift

• Deposition will happen when transported material is dropped from the sea water
• This occurs when the velocity (speed) of the water flow slows down
• This means there is not enough force to hold/suspend the material in the water anymore, and it is dropped onto the ground
• Beaches are formed of sediment deposited in bays
• Saltmarshes and mudflats are formed in sheltered estuaries, usually behind spits

Beaches

• Beach formation usually occurs in the summer months when the weather is calmer
• Form in sheltered areas such as bays through deposition via constructive wave movement, where the swash is stronger than the backwash
• Blown sand can create sand dunes at the backshore of a beach
• When a constructive wave carries sediment up the beach, the largest material is deposited along the upper reach of the swash
• As the backwash moves back down the beach, it loses water and therefore energy as it travels due to the porosity of the sand
• Consequently, the deposition of sediment gets progressively smaller, and the beach is therefore, sorted by wave deposition, with the smallest mud particles settling in the low-energy environment offshore
• If a destructive wave forms due to a storm, then large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm

Sediment deposition

Spits

• An extended stretch of sand or shingle that extends out to sea from the shore
• Spits occur when there is a change in the shape of the coastline
• Or the mouth of a river, which prevents a spit forming across the estuary
• A spit may or may not have a 'hooked' end, depending on opposing winds and currents
• A good example is Spurn Point, which stretches for three and a half miles across the Humber Estuary in the northeast of England

Stages of formation

• Sediment is transported by the action of longshore drift
• Where the coastline changes direction, a shallow, sheltered area allows for the deposition of sediment
• Due to increased friction, more deposition occurs 
• Eventually, a spit slowly builds up to sea level and extends in length
• If the wind changes direction, then the wave pattern alters and results in a hooked end
• The area behind the spit becomes sheltered
• Silts are deposited here to form salt marshes or mud flats

Spit formation

Bars

• When a spit grows across a bay, and joins two headlands together
• A bar of sand is formed (sandbar)
• Sandbars can also form offshore due to the action of breaking waves from a beach

Image showing how longshore drift contributes to spit and bar formation