Coasts GCSE Revision

Erosion : breaking down of the rock particles being carried downstream by the river.

TYPES OF EROSION:•Hydraulic Action- water continually hits the rocks and compresses air into cracks, when the wave goes out the air rushes out and rock breaks away. The cracks thus get bigger. •Abrasion (or corrasion)-waves break and hurl rocks and debris at the rocks to erode. •Corrosion/ Solution- Chemicals within the water wear away rock. Sea water and weak acids dissolve the rock and minerals. •Attrition- When rocks hit one another and get smaller and break up.

WEATHERING Weathering- the breakdown and decay of rock by natural processes, without the involvement of any moving forces.•Chemical Weathering- Breakdown of rock by changing its chemical composition (Acid Rain)•Mechanical Weathering- Breakdown of rock without changing its chemical composition( freeze-thaw) •Biological Weathering- Roots of vegetation can grow into cracks in a rock and split the rock apart.

COASTAL PROCESSES• Swash- the process of the wave coming in.• Backwash- the process of the wave going out.• Constructive waves have strong swash and weak

backwash. They break about 6-9 times a minute, and are long in relation to their height. They need calm conditions. (BUILD UP THE COASTLINE)

• Destructive waves have a weak swash and strong backwash. This erodes pebbles and shingle. High in proportion to their length. -happen in Autumn or Winter (ERODE THE COASTLINE)

• Fetch- the distance a wave has travelled.

WAVE CUT PLATFORMS 1. Weather weakens the top of the cliff.2. The sea attacks the base of the cliff forming a wave-cut notch.3. The notch increases in size causing the cliff to collapse.4. The backwash carries the rubble towards the sea forming a

wave-cut platform.5. The process repeats and the cliff continues to retreat.

• Cliff Recession-The process of a cliff getting small and falling apart.

• Causes of Cliff Recession-• Erosion- Hydraulic Action, Abrasion• Geology- Soft rock, Resistant Rock• Fetch- Destructive Waves, Constructive

Waves• Impermeable rock- can’t absorb water• Permeable rock- takes in water

CLIFF COLLAPSES ARE MASS MOVEMENTSMass Movement- the downslope movement of material due to gravity.

Slides - Material shifts in a straight line.

Slumps – material shifts with a rotation

Rockfalls- material shifts vertically

BAYS AND HEADLANDS

FORMATION OF A COVE • When alternating bands of hard and soft

rock running parallel to the coast (e.g. LULWORTH COVE IN DORSET)

EROSIONAL AND DEPOSITIONAL PROCESSES CHANGING A LANDFORM

OVERTIME • Caves occur when waves force their way into cracks in the cliff face.

The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.

• If the cave is formed in a headland, it may eventually break through to the other side forming an arch.

• The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.

• The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.

• One of the best examples in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.

THINGS THAT AFFECT THE SIZE AND ENERGY OF A WAVE:

– Length of time the wind is or has been blowing

– Strength of the wind– Fetch- distance of water over which

the wind has blown to produce a wave.

– Other waves

LONGSHORE DRIFT Longshore drift- material movement along a coastline. (takes material with it)

•Waves move towards the coast at an angle, as they break, swash carries material up and along the beach at the same angle. As the swash dies away, backwash and material fall at 90° because of gravity. Material goes in a zig-zag pattern. The prevailing wind is South Westerly and the backwash continues at 90°. •Longshore drift is continuous and can take a lot of a beach.

PROCESSES OF TRANSPORTATION

Solution Minerals are dissolved in sea water and carried in solution. The load is not visible.

Suspension Small particles are carried in water, eg silts and clays, which can make the water look cloudy.

Saltation Load is bounced along the sea bed, eg small pieces of shingle or large sand grains.

Traction Pebbles and larger sediment are rolled along the sea bed.

DEPOSITIONWhen the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash and is associated with constructive waves.Deposition is likely to occur when:•waves enter an area of shallow water.•When a wave loses energy •waves enter a sheltered area, eg a cove or bay.•there is little wind.•there is a good supply of material.

COASTAL AND DEPOSITIONAL LANDFORMS

BEACHES Beaches are areas of sand, pebbles and shingle that are formed by deposition produced by wave processes.  Beaches are by no means uniform and contain a huge variety of sediment types and sizes, and have many different shapes.Gently sloping beaches are formed by strong destructive waves that backwash more material away from the beach that they swash up the beach.Steeply sloping beaches occur by constructive waves that swash more material up the beach than they backwash away, building up a steep beach gradient.

Features Spits Tombolos Bars

What is it? a ridge of sand and shingle projecting from the mainland into the sea

a ridge of sand and shingle joining the mainland to an island

a ridge of sand and shingle which has joined two headlands, cutting off a bay

How does it form?

when there is a break in the coastline and drop in energy, long-shore drift deposited the material and build up spit

formed when spit continue to grow outwards connecting the mainland to the offshore island just like bridges

(a)form when a spit grows the whole way across a bay (b) a sandbank develops offshore, parallel to the shore until it joins the mainland 

Example Hurst Castle Spit

Isle of Portland Slapton Sands 

CASE STUDY : DORSET• Durdle Door - cave, arch • Lulworth Cove• Chesil Beach- tombolo,

lagoon • Swanage and Studland

bay – stack, stump

WHY SHOULD WE PROTECT THE COAST

METHODS OF PRESERVING THE COAST

ARE THE METHODS SUSTAINABLE ?