Coastal Landforms (DP IB Geography)
Revision Note
Written by: Grace Bower
Reviewed by: Bridgette Barrett
Erosion Landforms
Headlands and bays
Headlands and bays form at discordant coastlines:
Different types of rock alternate along the cliff face
The rock runs perpendicular to incoming waves
Softer rocks, like clays, erode more easily than harder rocks, like chalk
Bays form where softer rock is prevalent due to wave erosion:
Bays are curved, partly enclosed inlets of water
Bays often contain beaches
Harder, more resistant rocks leave headlands sticking out at sea
Formation of a bay and headland
Cliffs and wave-cut platforms
Cliffs are vast walls of rock found on the coastline
Constructive waves and softer sediment help form gentle, sloping cliffs
Destructive waves and resistant rock help form steep cliffs
Wave erosion processes, like hydraulic action and abrasion, wear away at the base of the cliff
Wave refraction causes the highest wave energy to focus on the headland
Waves break near the bottom of the cliff, so wave power is stronger
Repeated erosion at the base of the cliff forms a wave-cut notch
This notch widens with further erosion
Sub-aerial weathering weakens the top of the cliff
These combined processes cause the top of the cliff to collapse:
Over time, this process repeats, causing the cliff to retreat
Backwash brings the cliff material outwards towards the sea, forming a wave-cut platform
Formation of a wave-cut platform
Cave, arches, stacks and stumps
Wave and sub-aerial processes wear away at headlands, causing weaknesses
These weaknesses expand into cracks, eventually growing into larger gaps or caves
Continuous erosion and weathering from both sides of the headland will form an arch
With wave erosion at the base and weathering at the top, the arch will give way and collapse
This leaves behind a long, vertical piece of rock out at sea, called a stack
Erosion undercuts the base of a stack. Weathering continues from above, until the stack collapses, leaving behind a stump
Formation of a cave, arch stack and stump
Examiner Tips and Tricks
Make sure you know what these landforms look like. Practice drawing these landforms with their labels – you might be asked to draw them or analyse an image in the exam
Deposition Landforms
Beaches
Beaches are the buffer point between the ocean and the land
Constructive waves have a stronger swash, moving more sediment up the coastline:
Lots of larger sediment builds up at the back of the beach
Constructive waves have a weaker backwash, so deposit sediment more easily:
The water also percolates into deposited sediment, so less water returns with the backwash
Constructive waves occur more in summer, so beaches build up during this season (beach accretion)
Destructive waves take away sediment from the beach, typically during the winter (beach excavation)
Other landforms can form on beaches:
Ridges – raised areas along the beach
Runnels – dips along the beach
Berms – ridges that represent the high tide mark
Cusps – arc-shaped indents or hollows on the beach
Sediment moves along the beach through longshore (littoral) drift, controlled by prevailing winds
The differing angles of prevailing winds can produce different types of beaches:
Swash aligned – waves hit parallel to the shore and there is less longshore drift. Beaches are large and wide, with landforms like berms and sand dunes
Drift aligned – more influenced by longshore drift, moving sediment along the coast. Produces more narrow beaches, and other depositional landforms like spits and bars
Cross section of a beach profile
Spits
A spit is an elongation of beach sediment, connected to the mainland and jutting out to sea
Longshore drift transports and deposits sediment as it moves along the coastline
Waves deposit sediment if the coastline changes, e.g. changes direction or reaches a river:
Waves lose energy due to friction or counter-currents
This material builds up over time, extending outwards into the sea
Depending on the direction of the prevailing wind, the spit can curve inwards at the end
Salt marshes can develop behind the spit where there is protection from wind and waves
Formation of a spit
Bars, tombolos, lagoons and barrier islands
Bars are spits that join two separate headlands together
They are more visible during low tide
During high tide, bars can make the water shallower, so the wave breaks sooner
This can cause a lagoon to form in a bay behind the bar
If a spit joins a mainland with an island, this forms a tombolo
Barrier islands form parallel to the coast. They are areas with lots of built-up sediment
Barrier islands can contain beaches, sand dunes and even forests
Diagrams showing different landforms of deposition
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