Welcome to coolgeography.co.uk
Back to Main Back to GCSE Back to Coasts

Erosion Landforms

Characteristics and formation of headlands and bays, cliffs and wave cut platforms, caves, arches and stacks.

Stacks, stumps and caves
Coves
Bays and headlands
Cliffs

1) Take a test at BBC Bytesize

2) Try these quizzes from Fife education

3) Coasts questions from s-cool.co.uk

4) Try Mr G's lights out exercise - look for evidence of weathering and coastal erosion and write the evidence down

 

5) Try this hot potatoes exercise on Cliff formation

6) Have a go at this Stacks exercise.


6. Bays and headlands by rgamesby  

4. Stacks by rgamesby  
Coastlines are littered with the evidence of erosion and the power of the sea.  Erosion makes the coastline varied and interesting, and often give the coastline its "wow" factor. For each landform you need to understand how processes of weathering (freeze thaw, hydration, biological, salt crystallisation), mass movement (slumping, slides, rock falls) and erosion (Hydraulic Action, Corrasion, Corrosion) contributes to the formation.
You need to know about:

Stacks, stumps and caves

These features are formed on cliffs or headlands. Waves attack vertical lines of weakness in the rock known as Faults. Processes such as hydraulic action and abrasion widen these faults into cracks and eventually the waves will penetrate deeply enough to create caves.

Over time, the cave will be eroded into an arch, accessible to the sea on both sides.  Weathering will also play a role, with physical weathering processes such as freeze thaw and salt crystallisation and chemical processes such as carbonation weakening the rock surrounding the cave or arch making it more susceptible to mass movement and collapse.

Finally, the erosion and weathering continues and the arch collapses leaving behind a stack (a vertical column of rock) .  These stacks can be attacked further, and eventually the stack may collapse to leave a low lying stump.

Back to the top of the page

Diagram of stack formation
Old Harry
Lulworth Cove, on the Dorset coast Coves

Coves form where rock runs in  bands horizontal to the direction  of wave attack. There is a band of resistant rock closest to the sea and a band of less resistant rock inland.

The waves seek out faults in the hard rock and erodes using the processes of abrasion/corrasion and hydraulic action through to the soft rock behind.

Wave processes erode the softer rock faster and this leaves a circular cove with a narrow entrance where the sea enters. The waves are also refracted within the cove, spreading out to erode in all directions.

A good example of this is Lulworth cove.  

Back to the top of the page

Bays and headlands

In areas where the geology or rock type runs at right angles to the coastline, bays and headlands can be created.  If there are alternating bands of harder and softer rock running at right angles to the sea, the sea will erode these bands at different rates (called differential erosion).  Hydraulic action, abrasion and corrosion are more effective at eroding the softer rock, particularly during storms, and this will erode further inland than the harder rock.  During calmer weather and no stormy periods, the hard rock will absorb a lot of the wave energy and refract or bend the waves into the area with the softer rock, allowing sediment to be deposited and accumulate as beaches.  The net result of this over long periods of time is that the hard rock is left jutting out to sea as a headland, and the softer rock is eroded into curved sand filled bays.

Old Harry, Studland and Swanage bays - Geology The headland, picture taken looking at Old Harry Rocks  
The 2 images above show how the chalk of Old Harry Rocks sticks out to sea as a more resistant headland, whereas the clays and sans of Studland and Swanage bays have been eroded more to form bays.
Back to the top of the page

Cliffs and cliff retreat

A cliff is a vertical, near vertical or sloping wall of rock or sediment that borders the sea.  They generally differ in their angle of slope because of their rock structure and geology, but the processes involved in their formation are the same. 

Marine erosion processes attack the foot of the cliff and cause the erosion at a wave cut notch.  Waves can pound this area causing fragments to break off, and the water can also trap air in pore spaces, faults and crevices, compressing the air which in turn exerts pressure on the rock causing it to break off. This process is known as hydraulic action. Another process that occurs is corrasion, where sediment and rocks in the sea water are hurled against the cliff face. 

 

All three of these processes erode the wave cut notch  at the base of the cliff undermining the whole structure of the cliff. These processes are variable and depend upon the fetch of the wave (the distance it travels over open water), wind speed and how many storms there a year, but they are more or less continuous over long periods of time.

Annottaed cliffs example from Holderness coast

Back to the top of the page

At the same time that the base of the cliff is being eroded, the cliff face and its structure are being weakened by sub aerial processes. Oxidation and carbonation are some of the chemical processes that can weaken the structure of the rock, and depending upon the climate physical processes such as freeze thaw and water layer weathering can take effect.  Over time this weakens the structure of the cliff face, and coupled with the erosion of the wave cut notch at a critical point this cliff face will succumb to the influence of gravity and collapse in a process of mass movement.  This material will then be carried away by the sea in the process of long shore drift by the transportation process of solution, suspension, saltation and traction (depending upon the particle sizes).

7. Cliffs by rgamesby


Harrys Rocks Studland Purbeck Dorset England in England 
Navigate the image and list all of the coastal features that you can see