Coastal Process & Features (Erosion, Transport & Deposition…
Coastal Process & Features
The disintegration of rocks. Where this happens, pile of rock fragments called
can be found at the foot of cliffs.
Water collects in cracks or holes in the rock.
At night this water freezes and expands and makes cracks in the rock larger.
When the temperature rises and the ice thaws, water will seep deeper into the rock.
After repeated freezing and thawing, fragments of rock may break off and fall to the foot of the cliff.
Seawater contains salt. When the water evaporates it leaves behind salt crystals.
In cracks and holes these salt crystals grow and expand.
This puts pressure on the rocks and flakes may eventually break off.
Caused by chemical changes. Rainwater, which is slightly acidic, very slowly dissolves certain types of rock and minerals.
Rainwater absorbs carbon dioxide from the air and becomes slightly acidic.
Contact with alkaline rocks such as chalk and limestone produces a chemical reaction causing the rocks to slowly dissolve.
Due to the actions of Flora and Fauna. Plant roots grow in the rocks. Animals such as rabbits, burrow into weak rocks such as sands.
Fragments of rock break away from the cliff face, often due to freeze-thaw weathering.
Blocks of rock slide downhill.
Saturated soil and weak rock flows down a slope.
Slump of saturated soil and weak rock along a curved surface.
Formation of Features of Coastal Erosion
Caves, Arches, Stacks & Stumps
Abrasion and Hydraulic action widen the joint to form a cave.
Waves make the cave larger until it cuts through the headland to make an arch.
The arch is then eroded and the roof becomes too heavy and collapses. This leaves a tall stack.
The stack is then eroded and collapses, leaving a stump.
Cliff and Wave-Cut Platforms
When waves break against a cliff, erosion close to the high tide line will wear away the cliff to form a wave-cut notch. Over a long period of time, usually hundreds of years, the notch will get deeper and deeper, undercutting the cliff. Eventually the overlying cliff can no longer support its own weight and it collapses.
Through a continual sequence of wave-cut notch formation and cliff collapse, the cliff will gradually retreat. In its place will be a gently sloping rocky platform called a wave-cut platform. A wave-cut platform is typically quite smooth due to the process of abrasion. However, in some places it may be scarred with rock pools.
Erosion, Transport & Deposition
Rock fragments carried by the sea knock against one another causing them to become smaller and more rounded.
Fragments of rock are picked up and hurled by the sea at a cliff. The rocks act like tools scraping and gouging to erode the rock.
The dissolving of soluble chemicals in rock. Eg. Limestone.
This is the
effect of pebbles grinding over a rocky platform often causing it to become smooth.
This is the power of the waves as they smash into a cliff. Trapped air is forced into holes and cracks in the rock eventually causing the rock to break apart. This explosive force of trapped air operating in a crack is called
Coastal Deposition takes place in areas where the flow of water slows down.
Waves lose energy in sheltered bays and where water is protected by spits or bars.
Here sediment can no longer be carried or moved and is therefore deposited.
This explains why beaches are found in bays, where the energy of waves is reduced.
Mudflats and Saltmarshes are often found in sheltered estuaries behind spits where there is very little flow of water.
The movement of sediment on a beach depends on the direction that waves approach the coast.
Where waves approach head on, sediment is simply moved up and down the beach.
But if waves approach at an angle, sediment will be moved along the beach in a "Zigzag" pattern
This is when rocks and heavy boulders are dragged along the sea bed. This usually occurs when the waves do not have enough energy to carry the material into the water.
This is when smaller boulders are bounced along the sea bed.
Material such as sand grains, are light enough to be carried along in the water in suspension.
Lime from chalk and limestone rocks dissolves and is carried in solution - invisible to the naked eye but can be seen by the milky appearance of the sea.