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

  1. Temp alternates above and below 0*C
  1. Water gets into rock that has cracks
  1. When water freezes it expands, putting pressure on rock
  1. 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

  1. Rainwater has CO2 in it, which makes it a weak carbonic acid
  1. 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

Deposited sediment forms Spits, Bars and Sand Dunes

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

Shingle beaches

Flat and wide

Sand particles small and the weak backwash can spread them out down the beach - creating a long, gentle slope

Steep and narrow

Shingle particles are large and the weak backwash can't move them back down the beach - creating a steep slope

Spits

Bars

Sand dunes

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

Spit joins two headlands together

Bar cuts off the bay between the headlands from the sea

A lagoon can form behind the bar

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

Identifying landforms caused by deposition

Caves and arches cant be seen because of rock above them

Stacks look like blobs in the sea

Sand beaches are shown on maps as pale yellow

Cliffs are shown on maps as little black lines

Wave-cut platforms are shown as bumpy edges along the coast

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

Soft Engineering

Do Nothing - Managed Retreat

Sea Wall

Gabions

Rock Armour

Groynes

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

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

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

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

Beach Nourishment and Reprofiling

Dune Regeneration

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

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

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

Parts of Holderness are Protected by rock armour and groynes

Defences saved Mappelton but caused conflict

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

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

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