Waves are the result of the wind blowing over the sea. As they approach land they break.
Explanation of Wave Movements
- Seabed interupts the circular orbital movement of the water
- As water becomes shallower, the circular motion becomes of elliptical
- This causes the crest of the wave to rise up and then eventually to topple onto the beach.
- The water that rushes up the beach is called swash
- The water that flows back towards the sea is called the backwash
Why are Waves Generally Larger in South West?
Wave energy depends on:
- The fetch
- The strength of the wind
- The length of the time over which the win has blown
Types of Waves
Backwash is always at RIGHT ANGLES to the beach. Due to gravity.
Swash is always on an angle due to the wind direction (major winds are south west)
Swash : The forward movement of a wave up a beach
Backwash : The backward movemnt of water down a beach when a wave has broken.
Swash and Backwash
- These landforms are formed on headlands
- Firstly, the sea attacks the foot of the cliff and begins to erode areas of weakness such as joints and cracks, through processes of erosion such as hydraulic action, wave pounding, abrasion and solution;
- Gradually these cracks get larger, developing into small caves;
- Further erosion widens the cave and where the fault lines runs through the headland, two caves will eventually erode into the back of each other forming an arch, passing right through the headland.
- A combination of wave attack at the base of the arch, and weathering of the roof of the arch (by frost, wind and rain), weakens the structure until eventually the roof of the arch collapses inwards leaving a stack, a stack is a column of rock which stands separate from the rest of the headland.
- The stack will continue to erode, eventually collapsing to form a stump which will be covered by water at high tide.
The Foreland (Dorset Coastline) is a great example of a headland which shows these features - there is a distinctive stack called Old Harry and a stump known as Old Harry's Wife.
A good example of a distinctive arch, also found on the Dorset Coast is Durdle Door
Hydraulic Action : This involes the sheer power of the waves as they smash onto the cliff. Trapped air is blasted into holes and cracks in the rock, evenutaully causing the rock to break apart. The explosive force of trapped air operating in a crack is callled cavitation.
Corrasion: This involves fragments of rock being picked up and hurled by the sea at a cliff. The rocks act like a arosive tool by scraping away the rock.
Abrasion: This is 'sandpaper' effect of pebbles grinding voer a rock platform, often causing it to become smooth.
Attrition: This is where rock fragments carred by the sea knock against one another, causing them to become smaller and rounder.
Solution: Some rocks are vulnerable to being dissolved by sea water. This is particuarlly true of limestone and chalk, which form cliffs in many parts of the U.K.
- Strong (lots of energy) swash
- Weak (less energy) backwash
- Deposition greater than erosion.
- Weak (not a lot of energy) swash
- Strong (lots of energy) backwash
- Erosion is greater than deposition
Long Shore Drift
Longshore Drift is a way of transporting pebbles and shingle across the beach. This is where the load gets taken by the swash at an angle then move back towards the sea with backwash. This is then repeated and then over a long time the pebble will have travelled across the beach.
The same as in Rivers
Traction: Rolling of large pebbles along the seabed
Saltation: a 'bouncing' motion of particles and pebbles which are too heavy to be suspended in the sea.
Suspenstion: Particles carried within the water as are too light to travel along seabed.
Solution: dissolved chemicles which are transported in the sea such as limestone and chalk.
Coastal Landforms (Headlands and Bays)
- In the original coastline there is alternating bands of rock.
- Erosion, hydraulic action and abrasion take place.
- As the hard rock is more resistant it takes longer to erode back than softer rock which erodes quicker
- The soft rock then form bays
- The hard rock forms headlands
Description of Caves, Arches, Stacks and Stumps
Coastal depostition takes place in eareas where the flow of water slows down. Sediments can no longer be carried or colled along and has to be deposited.
Coastal deposition usually occur in bays, where the energy of the waves is reduced on entering the bay/ This explains the presence of beaches in bays and accounts for the lack of beaches at headlands, where wave energy is much greater.
Landforms formed by Deposition (The Spit)
Bars (Slapton Ley in Devon)
Occasionally, long shore drift may cause a spit to grow right across a bay, trapping a freshwater lake or lagoon behind it.
Landforms formed by Deposition (The Spit)
Explanation of a formation of a Spit
Spit is a finger of new land made of sand and shingle, jutting out of the sea from the coast.
- As sediment is transported along the coast by long shore drift, it becomes deposited at a point where the coastline changes direction or what a river mouth occurs.
- Gradually as more and more sediment is deposited, the feature extends into the sea.
- Away from the coast, the tip is affected by waves approaching from different directions and the spit often becomes curved as a result.
- Over time, the sediment breaks the surface to form new land and a spit is formed.
- It soon becomes colonized by grass and bushes and eventually trees will grow
- On the landward sheltered side of the spit where the water is calm, mudflats and salt marshes form
- There are important habitats for plants and birds
- Being close to the sea lever, spits are vulnerable to erosion, especially during storms
Salt marsh: areas of periodically flooded low-lying coastal wetlands. They are rich in plants, birds and animals.
Cliffs and Wave-Cut Platforms
Explanation of Cliffs and Wave-Cut Platforms
- When waves break against a cliff, erosion close to the high tide line takes a 'bite' off the cliff to form a wave-cut notch.
- A wave-cut notch is a small indentation cut into a cliff roughly at the level of high tide caused by concentrated marine erosion at this level.
- The types of marine erosion are hydraulic action and corrosion.
- Over a long period of time, usually hundreds of years, the notch gets deeper until 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 line gradually retreats.
- In its place will be a gently sloping rocky platform called a wave-cut platform.
Features of a wave-cut platform
- Quite smooth due to abrasion
- In some places there might be rock pools
- If tehre are constructive waves it will be covered by sand or shingle
- Destructive waves will remove sand or shingle exposing the wave-cut platform
It is caused by
- Thermal expansion of the sea water as it absorbs more heat from the atmosphere
- The rate of global warming
What places could be affected?
- In the U.K, low-lying places will be affected like East Anglia
- Low -lying coastal plains such as Bangladesh
- Whole group of islands such as the Maldives (Indian Ocean)
More than 70% of the worlds population live of coastal plains, the effects of rising sea levels are likely to be devastating
Which Land Processes Shape our Coastline
Weathering: The break up or decay of rock sin their original place at or close to the Earth's surface.
- Starts with water collecting in pores in rock then at night this water freezes and expands by about 9%
- If water is in a confined space, the expansion creates stresses within the rock, widening any cracks that already exist.
- When the temperature rises and the ice thaws, the water seeps deeper into the rock along newly formed cracks. After repeated cycles, fragments of rock may become detatched and fall to the foot of the slope to collect as scree.
Mass movement: is the downhill movement of material under the influence of gravity.
Mass Movement (Continued)
Rockfall- Fragments of rock break away from the cliff face often due to freeze-thaw weathering.
Landslide- Blocks of rock slide downhill.
Mudflow- Saturated soil and weak rock flows down a slope.
Rotational Slip- Slump of saturated soil and weak rock along a curved surface
In the same way that sugar dissolves in tea, some mineral and rocks dissolve in rainwater.
Carbonation is similar to solution in that it dissolves. It affects rocks that are made up of calcium carbonate such as limestone and chalk.