Coasts

Depositional landforms/features

Deposition = laying down of sediment to form new features and landforms

Coasts are built up when deposition greater than erosion

Deposition increased when:

  • lots of erosion elsewhere on coast (results in lots of material available)

  • lots of transportation of material into area

Low energy waves (constructive) carry material to coast in strong swash but are not strong enough to take a lot away (weak backwash)

Beaches:

  • Beaches are found between high water mark and low water mark

  • Constructed from sand and shingle

  • Found in sheltered bays (waves refracted and loose energy)

  • sand beaches:

    • flat and wide

    • gentle gradient

    • small sand particles

    • ridges and runnels present = series of ridges and troughs running parallel to coast near low water mark. Formed by deposition during backwash and the runnels are formed when water runs back to ocean

  • shingle beaches:

    • narrow

    • steeper gradient

    • large particles (pebbles)

    • creates storm beaches (when spring tides throw largest material up onto back of beach)

    • berms present - built up by constructive waves when high tide cycle goes from spring to neap

    • cusps present = semi-circular depressions. Smaller, more temporary formed by collection of waves reaching same point - sides of cusp channel incoming swash into centre of depression producing stronger backwash which drags material down beach from centre of cusp

    • ripples = small, elongated ridge. Waves and currents flow across loose sand which dragged along bottom and is piled up to form ripples

  • 2 main types of beach:

    • Swash aligned beaches:

      • formed when waves approach parallel to coastline and wash and backwash move sediment up and down the beach

      • creates a wide beach with an even profile along the shoreline

    • drift aligned beaches:

      • formed by longshore drift when waves approach on an angle

Spits

  • higher up coast the coastline is erroded

  • erroded material transported down coast in LSD

  • material deposited where coastline/current changes direction as current slows

  • sediment builds up on sea floor over time and eventually breaks surface of water - permanent

  • as more sediment deposited it grows out further into sea

  • end of spit curved by action of waves approaching it from different directions

  • colonised by grass and bushes - mudflats and salt marshes form in sheltered area of spit (= habitats)

  • vulnerable to erosion

  • CS: Spurn head, Holderness coast

    • 3% of material eroded from holderness coast deposited at spurn point each year

    • 5.5km long

Bars

  • formed when a spit extends out to sea and joins together 2 headlands

  • lagoon forms behind bar

  • e.g. Slapton Ley, Devon

Tombolo

  • formed when spit extends out to sea from mainland and joins to an island

  • e.g. Chesil Beach

Barrier islands

  • long, narrow strip of sand/sediment that forms offshore and parallel to coastline

  • typically form chains

Cuspate forelands

  • formed by waves moving sediment and building up a spit, erosion creating a cusp and cusp crowing into triangle shaped piece of land

  • LSD from both directions makes sediment build up cusp on both sides

Erosion landforms

Mass movement - landslides

  • downslope movement of large block of material that moves as a coherent mass - retains internal structure until hitting base of slope

  • common on steep, wet slopes (e.g. coastline)

  • e.g. Hallsands, South Devon

Rotational slumping

  • soft rock overlays resistant rock

  • happen because:

    • marine processes erode and bottom of cliff

    • rainwater infiltrates cliff

    • slip plane created

    • weight of saturated clay cause slump

  • e.g. Holbeck Hall Hotel, Scarborough

Rockfalls

  • triggered by undercutting or freeze thaw weathering

  • e.g. Beachy Head, sussex

How is material transported by water:

  • traction - large pebbles/boulders rolled along seabed

  • saltation - medium particles bounce along seabed (light enought to be picked up for small periods of time)

  • suspension - smaller particles carried in suspension within water - floating

  • solution - dissolved chemicals

Weathering

  • chemical - weak carbonic acid in rainwater attacks limestone cliffs

  • mechanical - repeated freezing and thawing of water absorbed in previous rocks leads to cracks and breakdown in rock

  • biological - burrowing of plants and animals into rock at coast - weakens and breaks up rock

Longshore drift

  • gradual movement of sediment along a coastline

  • waves strike coasts at angle of prevailing wind and sediment deposited at same angle with swash

  • backwash perpendicular to coastline - moved sediment perpendicular

  • repetition moves sediment along coastline

Erosional landforms:

crack - hydraulic action

cave - hydraulic action

arch - 2 caves or 1 cave all the way through headland

stack - biological, freeze thaw weathering and erosion breaks down arch

stump - wave cut notch eroded until stack becomes unstable and topples over leaving stump - will be eroded by abrasion making it smaller and smoother

Geo

  • inlet, gully or narrow and deep cleft in face of a cliff

  • created by erosion along faults in rock

  • may have caves (leading to blow holes, or collapse)

Aeolian processes:

  • picking up, transportation and deposition of sediment by wind

  • carried relatively short distanced either by surface creep, saltation or suspension

    • surface creep = wind rolls sand along surface

    • saltation = temporarily lifts graind ‘bounce’

    • suspension - picked up and carried by wind

salt marshes

Mudflats:

  • develop of sheltered coastlines with no powerful waves - often in estuaries or landward of spit. Need to be in low lying areas that are submerged at low tide and has silt and clay sediment

  • fine particles in suspension undergo flocculation and individual clay particles clump (aggregate) together to form larger, heavier particles that fall to bed

  • flocculation = small colloidal particles settle out of suspension to become sediment in form of flakes

  • not permanent as very vulnerable to sea level changes

  • e.g. Morecambe bay - largest mudflat in England

Salt marsh:

  • tidal landform consisting of silt and mud

  • form in halosere environment (tolerant of salty conditions) between land and open salt water (upper coastal intertidal zone)

  • protect shorelines from erosion by buffering wave action and trapping sediments

  • complex plant succession categorised by wetland species such as reeds and rushes

  • conditions required: sheltered river estuaries/behind spits, low wave energy, fine sediment available, inter tidal mudflats present, flocculation occurs

  • factors affecting salt marsh development: weather (storms may erode), sediment supply (enhance/diminish), sea level, climate (affects species, growth, sea levels), wave type, tidal/river regime, human action (recreational, industrial, commercial)

  • e.g. Keyhaven

SEA LEVEL CHANGE

Glacial periods and glacial retreat - long term seas level change due to climate change

post glacial rebound = rise of land masses after removal of huge weight ice sheets during last glacial period

EUSTATIC - sea rising/falling

ISOSTATIC - land rising/falling

TECTONIC

sea level rise:

  • during glacial periods, temps fall and ice sheets and glaciers form on land = global eustatic fall

  • continental ice increases in size = localised isostatic depression = sea levels rise

  • temperatures rise during interglacials = melting ice = global eustatic rise

  • continental ice continues to melt and weight on land decreases = isostatic uplift

  • localised fall in sea levels rise- post glacial rebound

impacts of sea level rise on Kiribati

(33 islands in Pacific)

islands only 1m above sea level

many islands could disappear in next 50 years

sea level rising 1.2cm a year in some places = 4x more than global average

rising sea levels are contaminating water sources and affecting ability to grow crops

Emergent landforms -

  • raised beaches - isostatic change uplifts land forcing coastal features to rise above former level - forms relic cliffs e.g. Isle of Islay in scotland

  • marine platforms

Submerged landforms

  • Rias - drowned river valleys- rivers created v shaped valleys with high upland areas - as sea levels rise they floor river valleys leaving only high land visible e.g. sydney harbour

  • fjords - drowned glacial valley - as sea levels rise deep glacial troughs (u shaped valley) are submerged e.g. milford sound

  • dalmatian coastline - valleys run parallel to coastline are flooded so islands created that run parallel to coastline e.g. croatia

spring tide = earth sun and moon are in straight line = tide strongest

neap tide = moon and sun positioned 90 degrees to each other in relation to earth = tide weakes

sand dunes

Psammosere = ecological succession that began life on newly exposed coastal sand e.g. sand dune

climax vegetation = dominant mix of vegetation species that characterise an environment given time for colonisation to occur and reach stability

plant succession = directional change in types of plant species that occupy a given area through time (involves colonisation, establishment and extinction)

sand dune = small ridges/hills of sand found at top of beach above usualy maximum reach of waves

Sand dunes have gentle slope on windward side, crest at top and unstable, steep slip slope of sheltered side

at low tide sand dries out allowing prevailing winds to move loose sand up beach - large tidal range = more time to dry out

Sand dunes develop in

  • largely sandy beaches

  • large tidal zone

  • shallow beach gradient (good conditions for sediment transport)

  • persistent onshore winds to dry and move sand particles by saltation inland

How do sand dunes develop:

  • process of change from bare sand to forest called succesion

  • vegetation colonised in seres (series of stages)

  • final sere is in dynamic equilibrium with climatic environent e.g. temperate deciduous forest

  • pioneer species = first type of plant to colonise sand dunes near to sea in embryo dunes e.g. sea couch grass

  • embryo dune - fore dune - yellow dune - grew dune - dune slack - woodland

  • sand needs obstruction to accumulate around e.g. seaweed, driftwoods etc. - forms embryo dune

  • embryo dune must be colonised by plants to stabalise sand - extreme conditions (high pH, wind speed, salt spray etc.) = many dunes destroyed if not colonised (up to 1m)

  • fore dune - colonised by marram grass, lyme grass etc. - drought resistant plants - help trap more sand so dunes increase in height (up to 5m)

  • yellow dune - greater biodiversity of plants as conditions more favourable. As plants die and decay a humus layer builds up trapping water and nutrients (only slightly alkaline pH, more shelter, less spray), up to 80% of sand vegetated (5-10m)

  • grey dune - very stable - mosses and lichens fill remaining space - vegetation cover up to 100% - small shrubs e.g. brambles may appear. Much shelter, humus and soil begins to form (10+m and wider)

  • dune slack - found between mature dunes and may undergo waterlogging and surface water - well adapted plants e.g. cotton grass, rushes, creeping willow

  • mature dunes - climax vegetation develops

CS: SALTFLEEBY-THEDDLETHORPE DUNE

  • 1377 acres of sand dunes, salt marsh, sand and mudflats

  • home to dragon flies and water spiders

  • endangered animals such as Jack Toad and wading birds live here as well as rare plants such as Fairy flax

coastal management

½ of worlds population live within 60km of coastline

¾ of large cities are at coast

shoreline management plans

  • hold the line - sea defences stop erosion

  • advance the line - move coast further into sea with sea defences

  • managed realignment - allowing shoreline to move landward with control

  • no active intervention

hard engineering:

  • sea wall

  • groynes

  • rock armour

  • gabions

soft engineering:

  • beach nourishment

  • dune regeneration

  • land us management

Case studies

HOLDERNESS COAST:

  • fastest eroding coastline in Eurpoe - 1.8m a year:

    • rock type - cliffs made from boulder clay = less resistant to erosion and slumps when wet

    • naturally narrow beaches - give less protection to coast as doesn’t reduce power of waves

    • man made structures e.g. groynes - narrows uprotected beaches elsewhere even more

    • powerful waves - travel long distances over North Sea = long fetch = a lot of energy

  • Mappleton:

    • subject to intense erosion at 2m per year - resulted in access road being 50m from cliff edge

    • Use hold the line

    • Rock groynes:

      • £2 million on 2 rock groynes to protect main coastal road and Mappleton

      • granite imported from Norway

      • increasing wideness of beach to break waves faster

    • Added vegetation cover at cliff base (soft engineering)

    • Great Cowden

      • south of mappleton

      • rate of erosion increased significantly - terminal groyne syndrome - 2m to 10m per year

      • Sue Earl’s farm lost

    • Positives for coastal defenses at Mappleton

      • saves homes

      • saves farmland = food

      • build up beach = tourism = jobs and multiplier effect

    • Negatives

      • expensive and ugly

      • stop longshore drift to places further down coast = erosion - also increased flood risk

  • Hornsea

    • hold the line because:

      • wind turbines at Hornsea provide power to 1.4 million homes

  • Spurn point (spit formation)

    • 3% of sediment from Holderness coast deposited here each year