Coastal landscapes in the UK

Weathering - the breakdown of rocks where they are.

Erosion - when rocks are broken down and carried away by something. E.g, seawater.

Mechanical weathering 

• The breakdown of rock without changing its chemical composition. 

Freeze-thaw weathering 

1. Happens when the temperature alternates above and below 0 degrees. 

2. Water gets into rock that has crack. E.g, granite.

3. When the water freezes it expands, which puts pressure on the rock.

4. When the water thaws it contracts, which releases the pressure on the rock.

5. Repeated freezing and thawing widens the cracks and causes the rock to break up.

Chemical weathering - the breakdown of rock by changing its chemical composition. 

Dissolved by rain = carbonation.

Reacts with air = oxidation. 

Carbonation 

1. Rainwater has carbon dioxide in it, which makes it a weak carbonic acid.

2. Carbonic acid reacts with rock that contains calcium carbonate.

3. The rocks are dissolved by the rainwater.

Mass movement - the shifting of rocks and loose material down a slope. E.g, cliff. 

• It happens when the force of gravity acting on a slope is greater than the force supporting it.
• Cause coasts to retract rapidly.
• They're more likely to happen when the material is full of water - makes the material heavier.

Three types of mass movement 

Slides - material shifts in a straight line.

Slumps - material shifts with a rotation.

Rockfalls - material breaks up and fall down the slope.

1. Hydraulic power 

• Waves crash against rock and compress the air in the cracks.
• This puts pressure on the rock.
• Repeated compression widens the cracks and makes bits of rock break off.

2. Abrasion 

• Eroded particles in the water scrape and rub against rock, removing small pieces. 

3. Attrition 

• Eroded particles in the water smash into each other and break into smaller fragments. 
• Their edges also get rounded off as they smash together.

Swash - the movement of water up the beach.

Backwash - the movement of water back down the beach.

Destructive waves

• Waves that carry out erosional processes are called destructive waves. 
• They have a high frequency. 
• High.
• Steep. 
• Their backwash is more powerful than their swash. 
• This means material is removed from the coast.
• Created in storm conditions. 
• Created from big, strong waves when the wind is powerful and has been blowing for a long time.
• Short wave length.

Constructive waves 

• Created in calmer weather.
• Less powerful than destructive waves.
• Break on the shore.
• Deposit material, building up beaches.
• Swash is stronger than backwash.
• Have a long wavelength.
• Low in height.

Wavelength - the difference between two crests.

Waveheight - the height from the crest to the trough.

Wave frequency - how many waves there are.

Crests - the top of the wave.

Trough - the low between two waves.

Fetch - the distance over which the wind blows.

• Waves are created by wind blowing over the surface of the sea.
• As the wind blows over the sea, friction is created - producing a swell in the water.
• The energy of the wind causes water particles to rotate inside the swell and this moves the wave forward.

The size and energy of a wave is influenced by

1. how long the wind has been blowing

2. the strength of the wind

3. how far the wave has travelled (the fetch)

1. Waves cause most erosion at the foot of a cliff.

2. This forms a wave-cut notch which is enlarged as erosion continues.

3. The rock above the notch becomes unstable and eventually collapses. 

4. The collapsed material is washed away and a new wave-cut notch starts to form.

5. Repeated collapsing results in the cliff retreating. 

6. A wave cut platform is the platform that's left behind as the cliff retreats. 

• Soft rocks or rocks with lots of joints have low resistance to erosion.
• Hard rocks with a solid structure have a high resistance to erosion.
• Headlands and bays form where there are alternating bands of resistant and less resistant rock along a coast.
• The less resistant rock (e.g, clay) is eroded quickly and this forms a bay - bays have a gentle slope.
• The resistant rock (e.g, chalk) is eroded more slowly and its left jutting out, forming a headland - headlands have steep sides.

1.) Headlands are usually made of resistant rocks that have weaknesses like cracks.

2.) Waves crash into the headlands and enlarge the cracks - mainly by hydraulic power and abrasion.

3.) Repeated erosion and enlargement of the crack causes a cave to form.

4.) Continued erosion deepens the cave until it breaks through the headland - forming an arch. 

5.) Erosion continues to wear away the rock supporting the arch, until is eventually collapses.

6.) This forms a stack - an isolated rock that's separate from the headland. E.g, Old Harry, Dorset.

Material is transported along coasts by a process called longshore drift.

1.) Waves follow the direction of the prevailing (most common) wind.

2.) They usually hit the coast at an oblique angle (any angle that isn't a right angle.)

3.) The swash carries material up the beach, in the same direction as the waves.

4.) The backwash then carries material down the beach at right angles, back towards the sea. 

5.) Over time, material zigzags along the coast. 

Traction

• Large particles like boulders are pushed along the sea bed by the force of the water.

Saltation 

• Pebble-sized particles are bounced along the sea bed by the force of the water.

Suspension

• Small particles like silt and clay are carried along in the water.

Solution

• Soluble materials dissolve in the water and are carried along.

Depostion - when material being carried by the seawater is dropped on the coast. 

• Occurs when water carrying sediment slows down so that it isn't moving fast enough to carry so much sediment.
• Coasts are built up when the amount of deposition is greater than the amount of erosion.
• The amount of material that is deposited on an area of coast is increased when:

- There's lots of erosion elsewhere on the coast, so there's lots of material available.

- There's lots of transportation of material into the area.

• Low energy waves (slow waves) carry material to the coast but they're not strong enough to take a lot of material away - this means there is a lot of deposition and very little erosion.
• Waves that deposit more material than they erode are called constructive waves.
• Constructive waves have a low frequency.
• They're low and long.
• The swash is powerful and it carries material up the coast.
• The backwash is weaker and it doesn't take a lot of material back down the coast. This means material is deposited on the coast. 

• Beaches are found on coasts between the high water mark (the highest point on the land the sea level gets to) and the low water mark (the lowest point on the land the sea level gets to.)
• They're formed by contructive waves depositing materal like sand and shingle. 
• Sand and shingle beaches have different characteristics: 

1. Sand beaches are flat and wide - sand particles are small and the weak backwash can move them back down the beach, created a long, gentle slope.

2. Shingle beaches are steep and narrow - shingle particles are large and the weak backwash can't move them back down the beach. The shingle particles build up and create a steep slope.

Spits 

• Form at sharp bends in the coastline. E.g, river mouth.
• Longshore drift transports sand and shingle past the bend and deposits it in the sea.
• Strong winds and waves can curve the end of the spit (forming a recurved end.)
• The sheltered area behind the spit is protected from waves - lots of material accumulates in this area, which means plants can grow there.
• Over time, the sheltered area can become a mud flat or a salt marsh. 

Bars 

• A bar is formed when a spit joins two headlands together.
• The bar cuts off the bay between the headlands from the sea.
• This means a lagoon can form behind the bar.

Sand Dunes

• Sand dunes are formed when sand deposited by longshore drift is moved up the beach by the wind.
• Obstacles (e.g, driftwood) cause wind speed to decrease so sand is deposited. 
• This sand is colonised by plants and grasses. The vegetation stabilises the sand and encourages more sand to accumulate there, forming small dunes called embryo dunes.
• Over time, the oldest dunes migrate inland as newer embroyo dunes are formed.

Hard engineering - man-made structures built to control the flow of the sea and reduce flooding and erosion. 

Soft engineering - schemes set up using knowledge of the sea and its processes to reduce the effects of flooding and erosion.

Hard engineering - Sea Wall 

• A wall made out of hard material like concrete that reflects waves back to the sea.
• Prevents erosion of the coast.
• Acts as a barrier to prevent flooding.
• Creates a strong backwash which erodes under the wall.
• Sea walls are very expensive to build and to maintain.

Gabions 

• A wall of wire cages filled with rocks usually built at the foot of cliffs.
• The gabions absorb wave energy and so reduce erosion.
• They're cheap and easy to build.
• They're ugly to look at.
• The wire cages can corrode over time.

Rock armour 

• Boulders that are piled up along the coast. (Also sometimes called rip-rap)
• The boulders absorb wave energy and so reduce erosion and flooding. 
• Fairly cheap defence.
• Starve beaches futher down the coast of sand, making them narrower.
• Narrower beaches don't protect the coast as well, leading to greater erosion and floods.

Groynes 

• Wooden/stone fences that are built at right angles to the coast. 
• Trap materials transported by longshore drift.
• Create wider beaches which slow the waves.
• This gives greater protection from flooding and erosion.
• They're a fairly cheap defence. 
• They starve beaches further down the coast of sand, making them narrower.
• Narrower beaches don't protect the coast as well, leading to greater erosion and floods.

Beach nourishment and reprofiling 

• Sand and shingle from elsewhere/ lower down the beach that is added to the upper part of beaches. 
• Creates wider beaches which slow the waves.
• Gives greater protection from flooding and erosion.
• Taking material from the seabed can kill organisms. 
• Very expensive defence, has to be repeated.

Dune regeneration 

• Creating or restoring sand dunes by either nourishment or by planting vegetation to stabilise the sand.
• Sand dunes provide a barrier between the land and the sea.
• Wave energy is absorbed which prevents flooding and erosion.
• Stabilisation is cheap.
• The protection is limited to a small area.
• Nourishment is very expensive.

Managed retreat

• Areas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be of low value - eg places not being used for housing or farmland.
• The advantages are that it encourages the development of beaches(a natural defence) and salt marshes (important for the environment) and cost is low.
• Managed retreat is a cheap option, but people will need to be compensated for loss of buildings and farmland.