Coastal erosion processes create a number of significant landforms. There are a number of factors which affect the rate of this erosion: i) Rock Type – A more resistant rock, such as granite, will be eroded slowly, whilst a less resistant rock, such as clay or mud, can be eroded very quickly. ii) Jointing / Faulting – The more faults and joints a rock has the more susceptible it is to erosion, both from coastal and sub-aerial processes.
Coastal Rock Arrangement – A coastline with rocks that run parallel to the coast is called a concordant or “Pacific” coastline. One that has rocks running at right angles to the coast is called a discordant or “Atlantic” coastline.
HARD ROCK HARD SOFT ROCK SOFT HEADLAND BAY DISCORDANT COASTLINE
Headlands and Bays - Formed on an Atlantic (discordant) coastline due to the softer rock being eroded quicker than the harder rock. - Beaches form in the bays where the soft rock has been eroded away. - Headlands of more resistant, hard rock are left behind.
The sea uses its four erosion methods during high and low tide to create a notch. This means the cliff above is unsupported and collapses – retreating inland. This process is called ‘UNDERCUTTING’. The cliff is vertical and steep.
Cliffs & Wave Cut Platforms - Cliffs are formed when destructive waves attack the bottom of the rock face between high and low water mark. - The area under attack is eroded using the major processes of coastal erosion. - Points of weakness, such as faults and joints are attacked most, and eventually a wave-cut notch is gouged out.
The rock above overhangs the notch, and as it is cut deeper into the rock, gravity causes the overhanging rock to collapse. - The loose rocks are removed by the sea and transported along the coast by long shore drift. - The whole process of undercutting the cliff begins again. - As the cliff is eroded backwards it leaves behind a wave-cut platform, at the level of the low water mark. - This platform is rarely eroded, as the waves energy is concentrated on eroding the area between the high and low water mark, and not the rock that is underneath them.
Caves, Arches, Stacks and Stumps - Mainly seen on headlands. - Waves start by attacking the main points of weakness in the rock: the joints and faults. - A point of weakness is increased in size until it becomes a cave. - The waves continue to attack the cave, which finally results in an arch being formed through the headland. - The arch is attacked both by coastal erosion and sub- aerial erosion and finally the roof of the arch falls into the sea. - This leaves behind a stack, which is then slowly eroded down to become a stump.
Unfortunately, the sea defences stop the erosion, but this allows mass movement time to takeover. Rainwater seeps into the porous TILL and causes ROTATIONAL SLUMPING.
Humans are affected by the retreat of the cliff (loss of land, housing, etc.) They erect sea defences which stop the erosion (groynes, revetments, gabion cages and anti-tank blocks.