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Coastal Landscapes in the UK (UK Coastal Landscape (Durdle Door (An arch.…
Coastal Landscapes in the UK
Coastal Weathering and Erosion
Rock is Broken Down by Mechanical and Chemical Weathering
Mechanical weathering
One main type of mechanical weathering that affects coasts - freeze-thaw weathering:
Breakdown of rock without changing its chemical composition
Temp alternates above and below 0*C
Water gets into rock that has cracks
When water freezes it expands, putting pressure on rock
When water thaws it contracts, which releases pressure on rock
Chemical weathering
Breakdown of rock by changing its chemical composition
Carbonation - type of chemical weathering that happens in warm and wet conditions
Rainwater has CO2 in it, which makes it a weak carbonic acid
Carbonic acid reacts with rock that contains calcium carbonate so the rocks are dissolved
Mass Movement
Shifting of rocks and loose material down a slope
Cause coasts to retreat rapidly
More likely to happen when the material is full of water - acts as a lubricant and makes material heavier
Slides - material shifts in a straight line
Slumps - material shifts with a rotation
Rockfalls - material breaks up and falls down slope
Waves wear away the coast using three processes of erosion
Hydraulic power - waves crash against rock and compress air in cracks
Abrasion - eroded particles in the water scrape and rub against the rock, removing small pieces
Attrition - eroded particles in the water smash into each other and break into smaller fragments
Destructive waves
High frequency - (10-14 waves per minute)
High and steep
Backwash is more powerful than swash, material is removed from coast
Coastal Landforms Caused by Erosion
Waves erode cliffs to form wave-cut platforms
Erosion at base of cliff
Forms a wave-cut notch, which is enlarged as erosion continues
Rock above notch becomes unstable and eventually collapses
Collapsed material is washed away and a new wave-cut notch forms
Repeated collapsing results in cliff retreating
Wave-cut platform is left behind
Headlands and bays form where erosion resistance is different
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/bays form where there are alternating bands of resistant and less resistant rock along a coast
Less resistant rock is eroded quickly and forms a bay which has a gentle slope
Resistant rock is eroded more slowly and its left jutting out, forming a headland which have steep sides
Headlands are eroded to form caves, arches and stackes
Headlands have weaknesses like cracks
Waves crash into headlands and enlarge the cracks - mainly by hydraulic power and abrasion
Repeated erosion and enlargement causes a cave to form
Continues erosion deepens the cave until it breaks through the headland - forming an arch
Erosion wears away the rock supporting the arch, until it eventually collapses - this forms a stack - an isolated rock that's separate from the headland
Coastal Transportation and Deposition
Transportation is the Movement of Material
Process called longshore drift
Waves follow direction of wind
Hit coast at an oblique angle
Swash carries material up the beach
Backwash carries material down the beach at right angles, back towards the sea
Over time, material zigzags along the coast
Four other processes of transportation
Traction
Saltation
Suspension
Solution
Deposition is the Dropping of Material
Material being carried by seawater is dropped on the coast - occurs when water carrying sediment slows down so it drops it
Coasts built up when deposition is greater than erosion
Constructive waves
Low frequency (6-8 waves per minute)
Low and long
Swash is more powerful and carries material up the coast
Coastal Landforms Caused by Deposition
Beaches formed by deposition
Found on coasts between the high water mark and the low water mark
Formed by constructive waves depositing material like sand and shingle
Sand beaches
Flat and wide
Sand particles small and the weak backwash can spread them out down the beach - creating a long, gentle slope
Shingle beaches
Steep and narrow
Shingle particles are large and the weak backwash can't move them back down the beach - creating a steep slope
Deposited sediment forms Spits, Bars and Sand Dunes
Spits
Form at sharp bends in the coastline
Longshore drift transports sand and shingle past bend and deposits it in the sea
Strong winds and waves can curve the end of the spit
Sheltered area behind the spit is protected from waves so lots of material accumulates in this area, which means plants can grow
Bars
Spit joins two headlands together
Bar cuts off the bay between the headlands from the sea
A lagoon can form behind the bar
Sand dunes
Formed when sand is deposited by longshore drift is moved up the beach by the wind
Obstacles cause wind speed to decrease so sand is deposited - this is colonised by plants and grasses. This vegetation stabilises the sand and encourages more sand to accumulate
Identifying Coastal Landforms
Identifying landforms caused by erosion
Caves and arches cant be seen because of rock above them
Stacks look like blobs in the sea
Cliffs are shown on maps as little black lines
Wave-cut platforms are shown as bumpy edges along the coast
Identifying landforms caused by deposition
Sand beaches are shown on maps as pale yellow
Shingle beaches are shown as white or yellow with speckles
Spits are shown by a beach that carries on out to sea
UK Coastal Landscape
Durdle Door
An arch. Erosion by waves opened up a crack in the limestone headland, which became a cave then a arch
Lulworth Cave
Small bay formed after a gap was eroded in a band of limestone. Behind the limestone is a band of clay, which has been eroded away to form a bay
Chesil Beach
A tombolo (type of bar) formed by longshore drift. It joins the Isle of Portland to the mainland. Behind it is a shallow lagoon called the Fleet Lagoon
Swanage Bay, The Foreland and Studland Bay
Two bays with beaches called Swanage Bat and Studland Bay. Areas of softer rock, in between them is a headland called The Foreland made from a band of harder rock. End of the headland has been eroded to become a stack called Old Harry and a stump called Old Harry's Wife
Coastal Management Strategies
Hard Engineering
Sea Wall
Wall made out a hard material like concrete that reflects waves back to sea
Prevents erosion of the coast and barrier to prevent flooding
Strong backwash, which erodes under the wall. Expensive to build and maintain
Gabions
Wall of wire cages filled with rocks
Absorb wave energy and so reduce erosion and flooding, fairly cheap
Ugly to look at and wire cages can corrode over time
Rock Armour
Boulders that are piled up along the coast
Absorb wave energy and so reduce erosion and flooding, fairly cheap
Can be moved around by strong waves, so need to be replaced
Groynes
Wooden or stone fences that are built at right angles to the coast - trap material transported by longshore drift
Create wider beaches which slow the waves, gives greater protection from flooding and erosion, cheap
Starve beaches further down the coast of sand, making them narrower
Soft Engineering
Beach Nourishment and Reprofiling
Sand and shingle from elsewhere
Creates wider beaches that slow waves, greater protection from flooding and erosion
Taking material from seabed can kill organisms, very expensive, has to be repeated
Dune Regeneration
Creating or restoring sand dunes by nourishment or planting vegetation to stabilise the sand
Sand dunes provide a barrier between the land and the sea. Wave energy is absorbed, stabilisation is cheap
Protection is limited to a small area. Nourishment is very expensive
Do Nothing - Managed Retreat
Removing current defences and allowing the sea to flood land behing
Over time the land will become marshland, which protects land from flooding and erosion
Cheap and easy strategy and doesn't need maintaining
Because land is lost to the sea, choosing areas to flood can cause conflicts
Coastal Management
Holderness Coast is Retreating
Erosion is causing the cliffs to collapse
Prevailing winds mean that the eroded material is moved south along the coast by longshore drift, exposing new areas of cliff to erosion
About 1.8m of land is lost to the sea every year
Over 11km of the Holderness coastline is managed using hard engineering strategies
Parts of Holderness are Protected by rock armour and groynes
In 1991, 450m of coastline around Mappleton had to be protected at a cost of £2 million, and using 61000 tonnes of rocks
Used rock armour and rock groynes
Defences saved Mappelton but caused conflict
The coastal management scheme was successful - the village and the B1242 road are no longer at risk
The rock groynes prevented sediment moving south along the coast by longshore drift, this increased erosion south of Mappeltion, and led to:
Loss of land
Loss of habitat for wildlife on Spurn Head
In 1999, a 1km stretch of coast near the gas terminal at Easington had to be protected by rock armour costing £6.6 million