Distinctive landscapes : coasts

What is a landscape and what makes a coast distinctive?

• Landscape = the visible features of an area: physical (relief, rivers, coast, vegetation) + human (buildings, roads, farmland) • Natural landscape = shaped by physical processes; built landscape = dominated by human structures; most UK coasts are a mix • Coasts are distinctive because of geology (rock type + structure → cliffs, bays, headlands), climate (wave energy, storms, weathering) and human activity (defences, tourism, settlement)

Geomorphic processes on the coast: weathering, mass movement, erosion, transport, deposition

• Geomorphic process = a natural process that shapes the land and creates landforms • Weathering = breakdown of rock in situ, no moving agent • Mass movement = downslope movement under gravity (sliding, slumping) • Erosion = wearing away by a moving agent (waves + the sediment they carry) • Transport = movement of sediment by waves + currents • Deposition = sediment dropped when energy falls • Sub-aerial processes = weathering + mass movement above the waves; they weaken the cliff so waves can undercut it → collapse

What controls wave energy? (fetch, wind, season)

• Size + energy of waves depends on fetch (distance of open water the wind blows over), wind strength and wind duration • UK prevailing wind = south-west → long Atlantic fetch → most powerful waves on south-west-facing coasts • Winter storms (depressions) = stronger winds for longer → larger, destructive waves • Summer = calmer, smaller, constructive waves

How does a wave break? Define swash, backwash, wavelength, frequency and gradient.

• Wave nears shore → base slowed by friction with the shallowing seabed, top keeps moving → wave steepens, topples + breaks • Swash = water + sediment up the beach; backwash = back down the beach under gravity • Wavelength = distance between crests; frequency = waves per minute; gradient = steepness (tall + short wavelength = steep)

Constructive waves

• Low, gentle gradient, long wavelength, low frequency (6-8 per minute) • Swash stronger than backwash • Long gap between waves → water percolates into the beach → backwash weak, only carries fine particles back • Deposit sediment → build the beach up (steeper, berms at high-tide mark) • More common in calm summer weather

Destructive waves

• Tall, steep, short wavelength, high frequency (10-12 per minute) • Backwash stronger than swash • Next wave arrives before the backwash drains → beach saturated → little percolation → strong backwash drags material out to sea (scouring) • Erode sediment → flatter, lower beach → waves reach the cliff base → more cliff erosion • Storm beach = ridge of boulders/shingle thrown above high tide by storm waves; berm = ridge built by constructive waves

Compare constructive and destructive waves

• Constructive: low, long wavelength, 6-8 per minute, swash > backwash, deposit sediment, build a steeper beach, mostly summer • Destructive: tall + steep, short wavelength, 10-12 per minute, backwash > swash, erode sediment, flatten the beach, mostly winter storms

Explain the four processes of coastal erosion

• Hydraulic action: waves force air into cracks → compressed → released as the wave retreats → repeated → rock weakens + breaks off • Abrasion: sand + pebbles hurled at the cliff scrape it like sandpaper; cuts the wave-cut notch • Attrition: sediment collides → smaller + rounder (boulder → pebble → shingle → sand); wears down sediment, not the cliff • Solution: slightly acidic seawater dissolves calcium carbonate rocks (limestone, chalk) and carries them away

What affects the rate of coastal erosion?

• Wave energy (fetch, wind, storms) • Rock type: soft erodes fast, hard erodes slowly • Geological structure: joints, faults + bedding planes are weaknesses • Beach: a wide beach absorbs wave energy and protects the cliff • Weathering + mass movement weaken cliffs • Human activity: sea walls reflect energy + scour the beach; groynes starve downdrift beaches; dredging removes sediment; building on cliff tops adds weight + drainage

Rock resistance and permeability

• Resistant rock (granite, basalt, hard limestone) erodes slowly → steep cliffs, headlands • Less resistant rock (clay, sand, shale) erodes fast → gentle slopes, bays • Permeable rock (chalk, sandstone) lets water through; impermeable rock (clay) does not • Permeable on impermeable → water builds up at the boundary → adds weight + lubricates → slumping/landslides • Chalk + limestone also dissolve in weak acid (chemical weathering)

Geological structure and cliff profile

• Joints, faults + bedding planes = lines of weakness exploited by hydraulic action + weathering • Rock dips towards the sea → blocks slide down bedding planes → landslides, gentler cliff • Rock dips inland → steeper, more stable cliff • Soft rock (clay): weathers easily, saturates + slumps → gentle rounded profile • Hard rock: steep near-vertical face until the base is undercut → rockfall

Explain the types of weathering on coastal cliffs

• Freeze-thaw (mechanical): water in cracks freezes + expands ~9% → pressure → thaws → repeats → crack widens → pieces break off; needs temperatures around 0°C + jointed rock • Carbonation (chemical): rain + CO2 = weak carbonic acid → reacts with calcium carbonate (limestone, chalk) → soluble calcium bicarbonate washed away; oxidation: iron in rock reacts with oxygen → rock crumbles • Biological: roots widen cracks; burrowing animals + nesting birds loosen material; lichens produce weak acids

Explain mass movement on cliffs: sliding, slumping and rainfall

• Sliding: block moves along a plane of weakness (bedding plane dipping to sea) when the base is undercut or lubricated → rockfall/landslide, straight scar, debris at base • Slumping: saturated soft clay → heavier + less friction → rotational movement along a curved slip plane → concave scar, hummocky base → gentler profile • Heavy rain: adds weight; water can't drain through impermeable clay → pore water pressure rises + lubricates → gravity overcomes friction; worse if the base is undercut

Explain how sediment is transported

• Traction: largest sediment (boulders) rolled or slid along the bed • Saltation: small pebbles, gravel + coarse sand bounce along the bed • Suspension: fine sand, silt + clay carried within the water (cloudy) • Solution: dissolved minerals (from limestone, chalk) carried invisibly • Type depends on particle size/weight + wave energy; storms can move larger particles

Explain longshore drift

• Waves approach at an angle (prevailing wind) → swash carries sediment up the beach at that angle • Backwash flows straight back down the steepest slope (at right angles to the coast) under gravity • Sediment moves in a zigzag along the coast in the direction of the prevailing wind (south coast of England: west → east) • Sediment budget: inputs (cliff erosion, rivers, offshore) vs outputs (drift, storms) → beach grows if inputs > outputs

What is deposition, and why does it happen in bays?

• Deposition = waves lose energy → drop the sediment they carry • Happens in sheltered areas (bays, behind spits), shallow water (friction), when wind/wave energy falls, at river mouths, or when the sediment load is too large • Constructive waves deposit because swash > backwash • Bays: wave refraction spreads energy across the bay (concentrated on headlands) → low energy → deposition → beach

Explain how headlands and bays form

• Concordant coast = rock bands parallel to the coast → fairly even erosion; discordant coast = alternate hard + soft bands at right angles to the coast → differential erosion • Soft rock erodes faster (hydraulic action, abrasion) → bay; resistant rock left sticking out → headland (e.g. Swanage Bay) • Wave refraction: waves slow in shallow water at the headland + bend → energy concentrated on the headland, spread out in the bay • Headland = steep cliffs, rocky, high energy; bay = curved, lower land, sheltered, often a beach

Explain cliff retreat, wave-cut notch and wave-cut platform

• Waves attack the cliff base between high + low tide → hydraulic action, abrasion + solution cut a wave-cut notch • Notch deepens → cliff above unsupported → collapses (gravity + weathering above) → backwash removes debris • Repeats → cliff retreats, leaving a gently sloping rocky wave-cut platform exposed at low tide • Platform widens → waves lose energy crossing it (friction) → erosion slows

Explain how caves and arches form

• Wave refraction concentrates energy on the headland • Hydraulic action + abrasion exploit cracks at the cliff base → cave; weathering above (freeze-thaw) weakens the rock • Cave deepens + erosion breaks through the headland → arch (e.g. Durdle Door, Dorset) • Arch base widened by erosion, roof thinned by sub-aerial weathering

Explain how stacks and stumps form

• Arch roof thinned by weathering above + erosion below → unstable → collapses → stack (isolated column, e.g. Old Harry Rocks) • Stack undercut by abrasion + hydraulic action, weathered above → collapses → stump (low, covered at high tide) • Sequence: headland → crack → cave → arch → stack → stump

Explain how beaches form and how sand and shingle beaches differ

• Beach = sand/shingle deposited between low + high tide; forms in sheltered, low-energy areas (bays) • Constructive waves: swash > backwash; water percolates → backwash weak → sediment left behind → beach builds up • Sediment supplied by cliff erosion, rivers + longshore drift • Sand beach = gentle, formed in very low energy; shingle beach = steeper, more energetic waves, drains quickly → swash weakened → shingle left behind

How is beach sediment sorted?

• Largest sediment deposited first, at the top of the swash (needs most energy to move) • Swash loses energy + volume (percolation) → progressively smaller sediment deposited; weak backwash only carries the smallest back down → sand at the low-tide end • Pattern: large + angular near cliff/top of beach → smaller + rounded towards the sea (more attrition) • Exceptions: storms, groynes, tides

Explain how sand dunes form

• Onshore wind blows dry sand from a wide sandy beach inland • Trapped by obstacles (driftwood, plants) → embryo dunes • Pioneer plants (marram grass) trap more sand; roots stabilise it; dead plants add organic matter • Dunes grow taller + more stable: embryo → fore → yellow → grey dunes

Explain how a spit forms

• Spit = long narrow ridge of sand/shingle attached at one end, extending into the sea or across an estuary (e.g. Spurn Point, Humber)

• Longshore drift moves sediment along the coast

• Where the coast changes direction (bend, river mouth) sediment carries on straight → deposited in sheltered, shallow water (waves lose energy)

• Ridge builds above sea level + grows in length • Behind the spit: sheltered → salt marsh/mudflats

Why do spits have hooked ends, not cross estuaries, and have salt marsh behind them?

• Hook: secondary wind/wave direction, or waves refracting round the tip, change the direction of drift → sediment deposited in a curve

Spit doesn't close the estuary: river flow + tidal currents remove sediment at the mouth

• Salt marsh: sheltered, low-energy water behind the spit → fine silt/clay deposited (mudflats) → salt-tolerant plants (samphire, cord grass) trap silt → surface builds above the tide

What are bars and offshore bars?

• Bar = ridge of sand/shingle across the mouth of a bay, joining two headlands • Forms when longshore drift builds a spit across the bay until it connects → traps water behind → lagoon (e.g. Loe Bar, Cornwall / Loe Pool) • Offshore bar = underwater ridge parallel to the shore, formed where waves break, lose energy + deposit sediment; can move onshore with constructive waves

Why is the coast managed?

• Protect people, homes, businesses, roads, farmland, tourism, habitats + heritage sites from erosion and flooding • Sea level rise + more frequent storms increase the risk • Cost-benefit analysis: is the value of what is protected greater than the cost of the defence?

Hard engineering vs soft engineering

• Hard = artificial structures (sea walls, groynes, rock armour, gabions): effective but expensive, intrusive, can change sediment movement elsewhere • Soft = works with natural processes (beach nourishment, dune regeneration): cheaper, more sustainable, blends in, but needs repeating + gives less protection in severe storms

Sea wall and rock armour: how they work, advantages and disadvantages

• Sea wall: concrete/stone wall, curved face reflects wave energy back to sea. + very effective, lasts decades, can be a promenade. - very expensive, unnatural, reflected waves scour the beach at its base (e.g. Blackpool) • Rock armour: large boulders at the cliff/wall base; gaps absorb + break up waves. + cheaper, quick to build, long-lasting, habitats. - rocks costly to transport, unattractive, hazard to people, may increase erosion further along (e.g. Mappleton)

Groynes, gabions and revetments: how they work, advantages and disadvantages

• Groynes: wood/rock barriers at right angles to the beach trap longshore drift sediment → wider beach. + relatively cheap, tourism. - starve downdrift beaches → more erosion there (e.g. Mappleton, Bournemouth)

• Gabions: wire cages of rocks at the cliff base. + cheap, easy, plants grow through. - short-lived (cages rust), weak against big waves, unsightly

• Revetments: sloping wood/concrete barriers absorb wave energy. + cheaper than sea walls. - costly vs soft engineering, need maintenance (e.g. Blackpool)

Beach nourishment, dune regeneration and cliff stabilisation: how they work, advantages and disadvantages

• Nourishment: sand/shingle added (dredged offshore) → bigger beach absorbs energy. + natural, tourism, cheaper. - repeated regularly, dredging harms seabed, less effective in severe storms (e.g. Bournemouth)

• Dune regeneration: plant marram grass + fence off → roots stabilise sand, dunes absorb wave/wind energy. + cheap, sustainable, habitats. - not for cliffs, ongoing management, damaged by storms/visitors (e.g. Sefton Coast, Formby)

• Cliff stabilisation: regrade slope, drainage, vegetation → less weight + lubrication → less mass movement. - expensive, doesn't stop undercutting

Managed retreat and do nothing: how they work, advantages and disadvantages

• Managed retreat (realignment): defences removed/breached → sea floods low-lying land in a controlled way → salt marsh/mudflats absorb energy. + cheap long-term, sustainable, habitat. - land, homes + farmland lost, compensation, controversial (e.g. Medmerry, West Sussex) • Do nothing (no active intervention): no spending, natural processes continue. + free, no sediment disruption. - land + homes lost, property values fall, hardship; used where value < cost (e.g. Happisburgh, Norfolk)

Shoreline Management Plans, sediment cells and knock-on effects

• SMP options: hold the line, advance the line, managed realignment, no active intervention → chosen for each stretch of coast using economic, social + environmental factors • Sediment cell = stretch of coast where sediment movement is largely self-contained (11 main cells in England + Wales) • Defences interrupt longshore drift → sediment trapped in one place → downdrift beaches starve + shrink → cliffs erode faster (e.g. Mappleton protected the village but increased erosion further along the coast) → plan for the whole cell

Why do people disagree about coastal management, and how does climate change affect the coast?

• Different priorities: residents + businesses want protection; councils + Environment Agency have limited budgets + use cost-benefit, NIMBYISM + tourism

environmental groups prefer soft engineering/managed retreat; landowners resist losing land

• Climate change: sea level rise (thermal expansion + melting ice) → waves reach further up the coast; more frequent, intense storms → larger destructive waves + storm surges → more erosion + flooding

Evaluate hard engineering, soft engineering and managed retreat

• Hard: strong, long-lasting protection where value is high (towns, roads, industry); but expensive, unnatural, disrupts sediment, encourages risky development, may not be sustainable with sea level rise → best in densely populated or economically important areas

• Soft + managed retreat: work with nature, cheaper, natural-looking, habitats, sustainable; but need repeating, less protection in severe storms, retreat = land/property loss + controversial → best where less valuable land is at risk; often combined with hard enginee