Landforms

• Geological Structure & Rock Type

  • Geology shapes the coastline over time, place and space
  • 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
  • Differences between hard and soft rocks will also impact the shape and characteristics of cliffs
• Hard Rock


  • High and steep cliffs
  • Bare rock and rugged
  • Boulders and rocks at foot of cliff
• Soft Rock


  • Generally lower and less steep cliffs
  • Smoother cliff face; evidence of slumping
  • Few rocks at foot of cliff; some sand and mud
• Effects of Rock Type on the Coastline

  1. Geology shapes the coastline vertically through the height and profile of a cliff

  2. Geology shapes the coastline horizontally with bays and headlands
• Headlands and bays


  • Occur where there are alternating bands of hard and soft rocks run perpendicular to oncoming waves (discordant coastline)
  • 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
• Headland


  • Cliffs along its sides
  • Projects out to sea
  • Usually longer than it is wide
  • Geology is of resistant rock
• Bay


  • Wide, open entrance from the sea
  • Roughly, semi-circular shape extending into the coastline
  • Land that is lower than the headlands surrounding it
  • May or may not have a beach
• Cliffs and wave-cut platforms


  • Soft rock erodes quickly and will form sloping cliff faces
  • Steep cliffs are formed where there is hard rock facing the sea
  • Wave-cut platform is a wide gently sloped surface found at the foot of a cliff
  • Wave-cut notch is formed as the sea attacks the base of a cliff between the high and low water mark
  • Undercutting of the cliff leads to instability and collapse of the cliff
  • Backwash of the waves carries away the eroded material, leaving behind a wave-cut platform
• Caves, arches, and stacks

  • Form in a headland because of wave action and sub-aerial weathering
  • Wave refraction concentrates erosive action on all sides of the headland
  • 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
• Exam Tip
• Wave refraction


  1. As waves approach the shore, their speed is reduced as they move along the sea floor

  2. This changes the angle of the waves, and they will turn so the crest becomes parallel to the coast
• Wave refraction


  The process where waves turn so the crest becomes parallel to the coast
• Erosional processes on a headland

  1. Hydraulic power

  2. Abrasion

  3. Corrosion
• Formation of a cave, arch, stack and stump

  1. Crack begins to widen

  2. Abrasion wears away forming cave

  3. Cave becomes larger and eventually breaks through to form an arch

  4. Base of arch becomes wider and thinner through erosion below and weathering from above

  5. Roof of arch collapses, leaving behind an isolated column of rock called a stack

  6. Stack is undercut at the base by wave action and sub-aerial weathering above, until it collapses to form a stump
• Attrition is not part of the formation of this feature
• Corrosion is an active part of the formation of these features, as all salt water is slightly acidic and most rock contains some soluble minerals that will react with the salt water
• Sub-aerial weathering (from above) also contributes to the collapse of the arch and stack
• Beach formation

  1. Occurs in the summer months when the weather is calmer

  2. Form in sheltered areas such as bays through deposition via constructive wave movement, where the swash is stronger than the backwash

  3. Blown sand can create sand dunes at the backshore of a beach

  4. Largest material is deposited along the upper reach of the swash

  5. Backwash loses water and energy as it travels due to the porosity of the sand, so deposition of sediment gets progressively smaller, and the beach is sorted by wave deposition, with the smallest mud particles settling in the low-energy environment offshore

  6. 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
• Swash


  The movement of water up the beach
• Backwash


  The movement of water down the beach
• Sand dune formation


  1. Windblown sand is deposited against an obstruction: Pebble or driftwood

  2. As more sand particles are caught, the dunes grow in size, forming rows at right angles to the prevailing wind

  3. Over time, the ridges of the dunes will be colonized and fixed by vegetation in a process called succession
• Pioneer species on sand dunes

  • Have to deal with: Salinity, Lack of moisture as sand drains quickly (highly permeable), Wind, Temporary submergence by wind-blown sand, Rising sea levels
• Coastal dune succession


  1. Embryo dunes

  2. Fore dunes

  3. Yellow dunes

  4. Grey dunes

  5. Mature dunes
• Embryo dunes


  Wind-blown dried sand is trapped by debris and deposition begins, with pioneer species like Lyme Grass and Sea Couch Grass beginning to colonise. They are very fragile and reach a maximum height of 1 metre.
• Fore dunes


  The embryo dunes bring some protection against the prevailing wind, allowing other species like Marram Grass to grow and stabilise the dune with its root system. They reach a maximum height of 5 metres.
• Yellow dunes


  Initially yellow but darken as organic material adds humus to the soil. Marram grass still dominates but more delicate plants and insects are found. 20% of the dune is exposed, down from 80%. Height does not exceed 8 metres.
• Grey dunes


  More stable, with less than 10% of exposed sand and a good range of biodiversity. Soil acidity and water content increase as more humus is added. Shrubs and bushes begin to appear. Height is between 8 - 10 metres.
• Mature dunes

  The oldest and most stable dunes, found several hundred metres or more from the shoreline. The soil can support a variety of flora and fauna such as oak trees and alders (climax vegetation). This is the final stage in succession which is known as the climax community stage.
• Spit formation


  1. Sediment is transported by the action of longshore drift

  2. Where the coastline changes direction, a shallow, sheltered area allows for deposition of sediment

  3. Due to increased friction, more deposition occurs

  4. Eventually, a spit slowly builds up to sea level and extends in length

  5. If the wind changes direction, then the wave pattern alters and results in a hooked end

  6. The area behind the spit becomes sheltered, and silts are deposited here to form salt marshes or mud flats
• Spit


  An extended stretch of sand or shingle that extends out to sea from the shore
• Bar formation


  1. When a spit grows across a bay, and joins two headlands together, a bar of sand is formed (sandbar)

  2. Sandbars can also form offshore due to the action of breaking waves from a beach
• Bar


  A ridge of sand formed across the mouth of a bay or river
• The geology of the Dorset coast is perfect for both erosional and depositional landforms, with bands of soft clay and harder limestone and chalk
• Erosional and depositional landforms on the Dorset coast


  • Durdle Door (arch formation)
  • Lulworth Cove (bay formation)
  • The Foreland (headland)
  • Old Harry and his wife (stack and stump)
  • Chesil Beach (pebble tombolo)