Coastal Landscapes (Edexcel GCSE Geography B)

Geological Structure & Rock Type

• 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

Erosional Landforms

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

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

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

UK's Coastal Climate

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 Types & Characteristics

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

Weathering

• 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

• 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
    

Transportation

• 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

Depositional Landforms

• 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

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

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