Geography Coasts Assessment

Fetch

Fetch

The distance the wind blows over the water

Backwash

The water that flows back towards the sea after a wave breaks

Swash

The water that rushes up the beach after a wave breaks

Amount of energy of a wave

• Wind speed

• How long the wind has been blowing

• Distance of sea the wind can blow over

How waves work

• Circular orbit in open water

• Friction with seabed distorts circular movement

• Top moves faster - elliptical

• Wave begins to break

• Backwash and swash from new and old waves

Constructive waves

• Strong swash

• Very weak backwash

• Low and long wavelength

• Carries and deposits

• Formed by storms 100kms away

Destructive waves

• Restricted swash

• Very strong backwash

• Closely spaced - can interfere

• High and steep

• Formed by local storms

Weathering

Breakdown and decay of rock by natural processes acting on rocks, cliffs and valley sides in situ.

Freeze thaw

Water collects in cracks of rocks and freezes and expands repeatedly while seeping further into the rock, causing fragments to break off

Soft weathering

Sea water evaporates to leave salt crystals ehich grow and expand in cracks in rocks causing pressure leading to bits of rock breaking off

Carbonation

CO₂ in rain makes contact with alkaline rocks (chalk and limestone) causing them to dissolve

Mass movement

The movement of rock, soil or mud down a slope under the influence of gravity, with heavy rain usually the trigger. The scale of movement is determined by the extent of weathering on the slope

Sliding

Large blocks of rock sliding down a cliff face as a landslide, triggered by heavy rain/ earthquakes

Slumping

Saturated or weak rocks collapse often along a curved surface

Rock falls

Often result due to freeze-thaw weathering to form a scree at the cliff foot

Hydraulic power

The power of the waves as they smash into a cliff and trap air into holes and cracks in the rock, eventually causing it to break apart, cavitation

Abrasion

The wearing away of cliffs or rocky platforms by rocks carried by the sea being dragged over the platform

Corrasion

Fragments of rock from the sea are hurled at the cliff

Attrition

Rock fragments knock against each other to become smoother and more rounded

Longshore drift

Movement of sediment on a beach due to wave direction moving the sediment along the beach in a zig zag pattern

Coastal deposition

Waves lose energy in sheltered bays where they are protected by spits and bars - sediment is deposited to form beaches

Headlands and bays

Form when rocks of different strength are exposed, weaker bands erode faster to form bays and resistant rocks form headlands

Wave cut notch

Formed when erosion wears away at a cliff, causing it to collapse, erode and retreat in a cycle

Caves, arches stacks and stumps formation

1. A joint/ fault forms in resistant rock

2. Abrasion and hydraulic action widen it to form a cave

3. Waves make the cave larger until it cuts through the headland to form an arch

4. Arch is eroded and the roof is too heavy so collapses

5. This leaves a tall stack, which over time erodes to become a stump

Bwa Gwyn

Arch formed by erosion on the Anglesey coastline - previously quarried for china clay

Beaches

• Formed due to coastal deposition from constructive waves

• Sandy = shallow, long and flat with sand dunes and tunnels

• Rock/ pebble = steep, short destructive waves, storms

Beach profile change

Berm levels in the backshore formed by constructive waves, bars and destructive waves

Sand dune formation

• Sand settles against obstacles to form a ridge

• The area facing the wind forms a crest as the sand become unstable and collapses

• This causes them to move further inland

• Can become bigger (marram grass)

• This stabilises the dunes and makes them more fertile as they decompose

Spit formation

1. Longshore drift transports sand along the coast

2. Coastline changes shape

3. Spit grows out into the sea

4. Spit is exposed to changes in wave and wind direction

5. Saltmarsh forms in sheltered water behind spit

Bar formation

Longshore drift causes a spit to grow across a bay - trapping a lagoon behind it, can form further offshore, can be driven onshore by rising sea levels

EXAMPLE: barrier beach Chesil Beach Dorset

Solution

Dissolved chemicals often derived from limestone or chalk

Suspension

Particles suspended within the water

Traction

Large pebbles rolled along the seabed

Saltation

Hopping/ bouncing of particles too heavy to be suspended

Concordant coast

Band of more and less resistant rock run parallel to the coast

Discordant coast

Bands of more resistant and less resistant rock run at right angles to the coast

Wave refraction

1. Waves change direction as they approach the shore along a discordant coastline

2. The faster moving parts refract towards the headland, concentrating more wave energy and increasing the rate of erosion

3. Low energy waves build beaches in the bays

Dorset Coast geology

• Portland limestone = cliffs

• Bagshot beds, Wealden clays and sandstone = bays

• Chalk = arches and stacks

Lulworth Cove

• Located along a concordant coastline

• Purbeck limestone is highly resistant + forms steep cliffs

• Lulworth cove = rapidly eroding clay behind limestone

Chesil Beach

• Bar that joins island + mainland

• Lagoon behind bar = barrier beach

Durdle Door

• Arch created when caves fully eroded

• Limestone + sandstone headland

The Foreland

• Strong chalk = resistant to erosion

• Cliffs, headland + Old Harry

Swanage and Studland Bay

• Bagshot, Wealden and tertiary beds with unconsolidated sands and clays

• Less resistant to erosion → bay formation

Holderness Coast - WHERE

• North England

• 61km between Humber Estuary (S) and Flamborough Head

• Waves can remove 7-10m of coastline

• One of the fastest eroding coastlines → geology

Holderness Coast - EROSION

• Powerful destructive waves over North Sea

• Wave refraction → Southern side of headland