CGP Coastal Landforms

• Some Coastal Landforms are Caused by Erosion
• Wave-cut platforms

  • Can form as the sea erodes the land
  • Over time, cliffs retreat due to the action of waves and weathering
  • Weathering and wave erosion cause a notch to form at the high water mark
  • The rock above the cave becomes unstable with nothing to support it, and it collapses
  • Wave-cut platforms are flat surfaces left behind when a cliff is eroded
• Headlands and bays

  • Form where there are bands of alternating hard rock and soft rock at right angles to the shoreline
  • The soft rock is eroded quickly, forming a bay
  • The harder rock is eroded less and sticks out as a headland
• Caves, arches, stacks

  • Weak areas in rock (e.g. joints) are eroded to form caves
  • Caves on the opposite sides of a narrow headland may eventually join up to form an arch
  • When an arch collapses, it forms a stack
• Some Coastal Landforms are Caused by Deposition
• Beaches

  • Form when constructive waves deposit sediment on the shore
  • Shingle beaches are steep and narrow, made up of larger particles
  • Sand beaches are wide and flat, formed from smaller particles
  • Berms are ridges of sand and pebbles about 1-2 metres high found at high tide
  • Runnels are grooves in the sand running parallel to the shore, formed by backwash draining to the sea
  • Cusps are crescent-shaped indentations that form on beaches of mixed sand and shingle
• Spits

  • Form where the coast suddenly changes direction, e.g. across river mouths
  • Longshore drift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out into the sea
  • Occasional changes to the dominant wind and wave direction may lead to a spit having a curved end (recurved end)
  • Over time, several recurved ends may be abandoned as the waves return to their original direction (compound spit)
  • The area behind the spit is sheltered from the waves and often develops into mudflats and saltmarshes
• Offshore bars and tombolos

  • Bars are formed when a spit joins two headlands together, across a bay or river mouth
  • A lagoon forms behind the bar
  • Bars can also form off the coast as sea level rises, remaining partly submerged (offshore bars)
  • A bar that connects the shore to an island (often a stack) is called a tombolo
• Barrier islands

  • Long, shallow islands of sand and gravel that parallel the shore and are detached from it
  • Probably formed from the last ice age, when ice sheets melted and sea levels rose, flooding the land and depositing beaches and bars offshore
  • Another theory is that the islands were originally bars, attached to the coast, which were eroded in sections, causing breaches in the bar
  • A lagoon or marsh often forms behind the barrier island, where the coast is sheltered from wave action
• Sand dunes


  • Formed when sand deposited by longshore drift is moved up the beach by the wind
  • Sand trapped by driftwood or debris is colonised by plants like marram grass, which stabilise the sand and encourage more to accumulate, forming embryo dunes
  • Over time, the oldest dunes migrate inland as newer embryo dunes are formed, reaching heights of up to 10 m
• Estuarine mudflats and saltmarshes


  • Form in sheltered, low-energy environments like river estuaries or behind spits
  • As silt and mud are deposited by the river or the tide, mudflats develop
  • The mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide
  • The plants trap more mud and silt, gradually building upwards to create an area of saltmarsh that remains exposed for longer and longer between tides
  • Erosion by tidal currents or streams forms channels in the surface of mudflats and saltmarshes, which may be permanently flooded or dry at low tide