Coastal Landforms

• Caves, arches, stacks and stumps

  • Erosional
  • Inputs - high energy, destructive waves caused by high winds, aeolian weathering, nearshore currents
  • Commonly formed on headlands because wave refraction causes energy to be concentrated on the sides of the headlands
  • Erosion attacks faults and joints to form a crack, sometimes aided by freeze-thaw weathering in colder climates
  • Over time, a cave is developed from erosion and weathering (mainly hydraulic action but also abrasion to a degree)
  • A cave reaches the other side of the headland due to further erosion, forming an arch
• Caves, arches, stacks and stumps

  • Continued erosion widens the arch and weakens its support, making it collapse and forming a stack - an example of rockfall, a sub-aerial mass movement process
  • Further erosion at the base of the stack leads to another collapse to form a stump, which may only be visible at low tide
  • Alternate theory - climate change increasing extreme weather such as storms, causing more freeze-thaw weathering
  • Small tidal range causes wave energy to be concentrated, causing more erosion and for the headland to retreat over time
• Caves, arches, stacks and stumps

  • Modification - if a storm event occurs, there is increased wind and wave energy, causing more erosion and therefore a deficit in the sediment budget, and a loss of equilibrium which the system needs to restore
  • Example - Flamborough Head, primarily made of chalk (strong lithology but porous and has primary permeability so more easily exploited by the waves)
• Wave-cut notches and platforms

  • Erosional
  • Inputs - wind from atmospheric circulation which influences kinetic wave energy, nearshore currents, destructive waves
  • Destructive waves break repeatedly on relatively steeply sloping coastlines
  • Undercutting occurs between the high and low water marks, forming a wave-cut notch
  • Continued undercutting weakens support for the rock strata above, which eventually collapses, producing a steep profile and a cliff
• Wave-cut notches and platforms

  • Regular removal of debris ensures the cliff profile remains relatively steep, and the cliff retreats inland parallel to the coast
  • As the cliff collapses, a layer of flat rock is left behind called a wave-cut platform
  • The platform typically has a slope of less than 4 degrees, which is often only fully exposed at low tide
  • Alternate theory - chemical weathering, at night algae release CO2 as photosynthesis is not occurring, making the seawater more acidic, causing more erosion
• Wave-cut notches and platforms

  • Platform can be eroded when the tidal range is 4m or less, causing erosion to be concentrated on a small area of the shore platform, forming a cliff
  • When platforms reach a length of 500m, the waves have further to travel in shallow water so waves slow down due to increased friction and break earlier before they can erode the base of the cliff
  • Increased sub-aerial and aeolian weathering, erosion and rockfall can speed up the process
  • Example - Selwicks Bay, Flamborough
• Headlands and bays

  • Erosional
  • Inputs - energy from the wind and waves
  • Wave refraction also encourages the development of headlands
  • Waves in deep water do not reflect the shape of the land, but as they approach the coast, they take the shape of it
  • The waves that approach the headland reach shallow water first
  • Friction between the waves and the seabed slow the waves down they become higher and steeper
  • Therefore the headland experiences increased erosion rates
• Headlands and bays

  • In the bays, low energy waves (which have experienced less friction due to the deeper bay) deposit material and build up sandy beaches
  • Longshore drift even transfers sediment from the headland
  • Headlands and bays are formed on discordant coastlines where rocks are structured at right angles to the sea
  • Because of this, differential erosion occurs
  • Rocks with a weak lithology, such as clays and sand are easily exploited by wave action
  • Processes such as hydraulic action and abrasion erode the weak rock, forming bays, which often contain a sandy beach
• Headlands and bays

  • Bands of more resistant rock such as chalk are not affected as much by freeze-thaw and chemical weathering, hydraulic action and abrasion, and rockfall
  • Modification - smaller tidal range makes the wave energy, and therefore the erosion more concentrated
  • Example - Flamborough Head, and a bay from Flamborough Head to the Humber Estuary
• Geos and blowholes

  • Erosional
  • Inputs - wave energy, biological and chemical weathering (rain), hydraulic action and abrasion, rockfall
  • Weak points of resistant geology are eroded more rapidly by wave action than the more resistant rock around them
  • Hydraulic action forces air and water into the joints, weakening the rock strata
• Geos and blowholes

  • Geos form as tunnel-like caves running at right angles to the cliff line, which, as they become enlarged by further erosion, may suffer from roof collapse, forming a geo
  • If part of the roof of a tunnel-like cave collapses along a master joint, it may form a vertical shaft that reaches the cliff top, known as a blowhole
  • In storm conditions, large waves may force spray out of the blowhole as plumes of aerated water
  • Example of a geo - Huntsman's Leap in Pembrokeshire
• Spits, bars and tombolos

  • Depositional
  • Inputs - sediment from waves and longshore drift, kinetic energy causing wave movement
  • Spits form through longshore drift, when the prevailing wind pushes constructive waves up the beach at an angle as the swash
  • Sediment is pushed up and dragged back down the beach in this way through longshore drift
  • Once the waves reach the end of the beach, sediment will be deposited and build up an extension of the beach as a spit which can later curve up, and this is called a recurved spit
• Spit, bars and tombolos

  • Bars are formed in a similar way, except they form across a bay, cutting the bay off from the rest of the ocean
  • Tombolos are formed when a spit connects the mainland coast to an island
  • Modification - a storm can cause all the landforms to be eroded and lose sediment, therefore changing the shape of the landform
• Deltas

  • Depositional
  • Inputs - fluvial and ocean sediment deposits, winds impacting on waves, tides
  • A delta forms where the river meets the sea
  • Requires a low-energy coastal environment where sediment inputs outweigh outputs
  • River material eroded through hydraulic action and abrasion
  • When rivers with a large fine sediment load meet the sea, they lose energy and deposit it, forming a delta
  • A continental shelf can encourage the formation of a delta as it encourages more deposition
  • River channel splits into smaller branches (distributaries)
• Deltas

  • Distributaries are often lined by levees with low-lying crevasse splays
  • They form as the river feeds into the sea and deposition occurs
  • Delta formation can change over time due to erosion
  • Three types - cuspate, arcuate and bird's foot
  • Cuspate - if there are regular ocean currents approaching the cost from each side, wave erosion wears down the edges of the delta forming a triangular-shaped delta e.g. Erbo Delta, Spain
  • Arcuate - where the currents are more uniform, the whole seaward edge of the delta is smoothed and rounded e.g. Nile Delta, Egypt
• Deltas

  • Bird's foot - less wave energy and erosion, sediment accumulation extends further out to sea e.g. Mississippi Delta, Gulf of Mexico
  • Gradient impacts on geomorphology - a steeper gradient builds up a coarse-grained delta and a lower gradient builds up a fine-grained delta
  • As the delta extends further into the sea, a shorter pathway to the sea is created, and therefore new lobes are created
  • Where waves are dominantly affecting the delta, the coast is smoothened due to erosion
  • Human engineering further up a river can influence the sediment load of the river, more deposition
• Beaches

  • Depositional
  • Inputs - terrestrial, fluvial and ocean deposits, stronger winds cause stronger waves and therefore more deposition
  • A beach is a narrow strip of land that separates a body of water from an inland area
  • They are formed when there is a positive sediment budget (inputs greater than outputs)
  • Can also form at rocky coastlines at the base of cliffs if sub-aerial processes (weathering and mass movement) are greater than the ability of wave processes to remove debris
• Beaches

  • Deposited sand and sediment (fluvial or terrestrial) can steepen a beach profile
  • Berms are formed in this way, when constructive waves alter the beach morphology by causing the movement of sediment up a beach
  • It is a ridge of material and it usually occurs across the backshore zone of a beach, common in the summer, but eroded by destructive waves in the winter
• Beaches

  • A cusp is the formation of sediment in the shape of an arc, and is believed to be created when wave patterns push sediment into repeated places
  • The processes of longshore drift may also be linked to cusp formation as sediment is transported via a pattern
  • Modification - if a storm or destructive waves erode part of a beach, an offshore bar may form, causing the waves to break before they reach the beach, and then the beach is able to build itself back up when normal wave conditions resume