coasts 2

• cornwall -

  • can withstand frequent winter storms without suffering rapid erosion due to resistant rock types
  • igneous rocks (basalt and granite)
  • older compacted sedimentary rocks (old red sandstone)
  • metamorphic rocks (slates and schists)
• the wash -

  • area of low, flat relief - coastal plain
  • largest estuary system in uk - formed by 4 rivers
  • range of habitats - tidal creeks, mud flats, marshes, lagoons
• southern and eastern uk coastlines -

  • in comparison with western and northern Britain - eastern and southern coasts consist of areas of weaker and younger sedimentary rocks (chalks, clays, sands and sandstone)
  • eastern uk - low lying sandy beaches (eg bamburgh beach)
• high energy coastlines -

  • form rocky coasts
  • in the uk - stretches of the Atlantic-facing coast where waves are powerful (eg Cornwall or north-western Scotland)
  • where rate of erosion exceeds rate of deposition
  • erosional landforms - headlands, cliffs etc
• low energy coastlines -

  • form sandy and estuarine coasts
  • in the uk - stretches of coast where the waves are less powerful or sheltered from large waves (Lincolnshire and northumberland)
  • where the rate of deposition exceeds rate of erosion
  • depositional landforms - beaches, spits and coastal plains
• coastal system -

  • driven by wave energy
  • inputs, processes and outputs
• coastal system inputs -

  • marine - waves, tides, storm surges
  • atmospheric - weather/climate, climate change, solar energy
  • land - rock type and structure, tectonic activity
  • people - human activity, coastal management
• coastal system processes -

  • weathering
  • mass movement
  • erosion
  • transport
  • deposition
• coastal system outputs -

  • erosional landforms
  • depositional landforms
  • different types of coasts
• littoral zone -

  • stretches out into the sea and onto the shore
  • zone - because tides and storms affect a band around the coast
  • constantly changing because of dynamic interaction between processes operating in the seas, oceans and on land
• littoral zone varying factors -

  • short-term factors - individual waves, daily tides and seasonal storms
  • long-term factors - changes to sea levels or climate change
• littoral zone sections -

  • backshore - usually above the influence of the waves
  • foreshore - inter-tidal or surf zone
  • nearshore - breaker zone
  • offshore - beyond influence of waves
  • backshore and foreshore are areas where the greatest human activity occurs and the physical processes of erosion, deposition, transport and mass movement largely operate
• sediment supply -

  • processes of weathering and erosion produce output in the form of sediment - then transported and deposited to produce coastal landforms
  • sources of sediment are complex
• sediment supply: the wash -

  • main source of sediment originates from cliffs eroding east of the wash (along north Norfolk coast) - cliffs retreated at 1m per year for 1000s of years - sandstone so 60% of sediment consists of sand
  • some sediment consists of tidal currents - pick up glacial deposits from shallow sea floor
  • erosion from holderness cliffs further north also provides sediment - carried southwards in suspension
  • 4 rivers discharge into the wash - bring very fine sediment
• classifying coasts -

  • geology - create rocky, sandy and estuarine coasts - also concordant and discordant
  • level of energy - creating high or low energy coasts
  • balance between erosion and deposition (which is more dominant process) - creates either erosional or depositional coasts and associated features
  • changes in sea level - creating either emergent or submergent coasts
  • no classification is definitive - eg Cornwall high energy coast is mainly rocky but with some stretches of sand and estuaries
• jurassic coast -

  • coast of south Devon and east Dorset
  • lulworth crumple - limestone folding - thin beds of purbeck limestone and shale are clearly visible in side of cliff - layers of rock were folded in response to tectonic movements 30 million years ago
• coastal morphology = related to underlying geology, rock type and geological structure (lithology)

  • lithology
  • relief - height and slope of land - affected by geology and geological structure
  • direct relationship between rock type, lithology and cliff profiles
• lithology = geological structure of the rock:

  • strata - layers of rock
  • bedding planes - natural breaks in strata caused by gaps in time during periods of rock formation
  • joints - fractures caused by contraction as sediments dry out or earth movements during uplift
  • folds - pressure during tectonic activity makes rocks buckle and crumple (eg lulworth crumple)
  • faults - the stress or pressure a rock is subjected to exceeds its internal strength (causes fracture) - faults then slip/ move along fault planes
  • dip - angle at which rock strata lie

  
• geology and rates of coastal recession -

  • igneous rocks - (eg granite) crystalline, resistant and impermeable
  • sedimentary rocks - (eg limestone, chalk, sandstone, shale) formed in strata - jointed sedimentary rocks (eg sandstone, limestone) are permeable - others (eg chalk) have air spaces between the particles making them porous - shale is fine grained and compacted making it impermeable
  • metamorphic rock - (eg marble, schist) very hard, impermeable and resistant
  • unconsolidated materials - loose (eg boulder clay of holderness coast) - not cemented together in any way and are easily eroded
• reasons for differing rates of coastal erosion -

  • strata projecting into sea as headlands - indicating resistance to erosion - some strata more permeable than others
  • geology and lithology
  • weathering and mass movement
• concordant coasts = where bands of more resistant and less resistant rock run parallel to the coast

  • Dorset coast - rock type varies between resistant purbeck limestone which forms steep cliffs - to less-resistant clays and sands
  • rock types alternate along coast
  • isle of purbeck - southern coast is concordant coast
  • lulworth cove - over time sea gradually eroded resistant purbeck limestone at entrance - rapid erosion of less-resistant clays behind limestone led to formation of a cove or bay
  • kimmeridge bay - cliffs consist less-resistant clay
• Dalmatian coasts = another type of concordant coastline

  • formed as a result of a rise in sea level
  • valleys and ridges run parallel to each other - when valleys flooded because of sea level rise, tops of ridges remained above the surface of the sea as a series of offshore islands that run parallel to the coast
  • eg Dalmatian coast in Croatia
• haff coasts = also consist of concordant features

  • long spits of sand and lagoons aligned parallel to the coast
• discordant coast = geology alternates between bands of more-resistant and less-resistant rock which run at right angles to the coast

  • isle of purbecks eastern coast is discordant - runs south from Studland bay to durlston head - more-resistant rocks emerge at the coast as headlands and cliffs, less-resistant rocks form bays
  • geology and geological structure of the isle of purbeck has influenced coastal morphology of its eastern coast:
  • chalk is strong and resistant to erosion so it has formed cliffs and a headland at the coast
• headlands and bays -

  • headlands = jut out into the sea (eg the foreland)
  • bays = lie between headlands (eg swanage bay)
  • commonly form when rocks of different strengths are exposed at the coast
  • more-resistant rocks (eg chalk, limestone - igneous/metamorphic rock) form headlands
  • weaker rocks (eg shale, clay) are eroded to form bays
• headlands and bays: affecting incoming waves -

  • headlands - force the incoming waves to refract or bend - concentrating energy at the headlands - increased waves erosive power which leads to a steepening of the cliffs and their eventual erosion into arches and stacks
  • bays - when waves enter a bay their energy is dissipated and reduced - leads to the deposition of sediment (sand or shingle) forming a beach
• headlands and bays: wave power -

  • headland - when waves approach, the depth of the water decreases - causes waves to get higher and steeper - velocity also reduces and they become closer together - increases erosive power
  • bays - when waves enter a bay, the water is deeper - therefore they don't lose their velocity as rapidly - lower and less steep than those of the headland - allows deposition rather than erosion to take place
• what causes waves?

  • form when wind blows over water
  • size is related to wind speed (greater speed, greater wave)
  • build up over time - storm waves increase in size over several days
  • wind creates frictional drag - produces movement in the upper surface of the water
  • water particles move in circular orbit as waves move (ripple) across the surface
• what happens when waves approach the coast?

  • water becomes shallower and the circular orbit of the water particles changes to an elliptical shape
  • the wavelength and velocity both decrease and wave height increases causing water to back up from behind
  • force pushes wave higher so it becomes steeper before spilling and breaking onshore
  • water rushes up the beach as swash and flows back as backwash
• swell waves -

  • some waves originate in mid-ocean and maintain energy for 1000s of miles
  • fetch = distance of water they move over - greater the fetch the larger the wave
  • uk coast - these mid ocean waves appear as larger waves among smaller locally generated waves (swell waves)
• constructive waves -

  • wave form - low surging waves with a long wavelength
  • wave break - strong swash, weak backwash
  • beach gain
• destructive waves -

  • wave form - high plunging waves with a short wavelength
  • wave break - weak swash, strong backwash
  • beach loss
• beach morphology changes -

  • beaches consist of loose material so morphology alters as waves change
  • seasonal changes in wave type create summer and winter profiles - sediment dragged offshore by destructive waves in winter and returned by constructive waves in summer
  • material along a beach profiles varies in size and type depending on distance from shoreline
• summer beach profile -

  • steeper - constructive waves more common then destructive
  • constructive waves less frequent so wave energy dissipates and deposits over a wide area (weakening backwash):
  • swash of a constructive wave deposits larger material at top of beach - creating a berm (usually of shingle)
  • as berm builds up, backwash becomes weaker - only has enough energy to move smaller material so beach material becomes smaller towards shoreline
• winter beach profile -

  • destructive waves occur at a higher frequency
  • berms are eroded by plunging waves and high-energy swash
  • strong backwash transports sediment offshore - depositing it as offshore bars
  • sometimes backwash exerts current known as a rip or undertow - dragging sediment back as the next wave arrives over the top
• winter storm Dawlish 2014 -

  • waves destroyed part of sea wall
  • left a section of rail Tracy dangling in mid air and cutting rail connection between Devon, Cornwall and the rest of the UK for 2 months
• abrasion -

  • when waves advance they pick up sand and pebbles from the seabed
  • when they then break at the base of the cliff the transported material is hurled at the cliff food - chips away at rock
• hydraulic action -

  • when a wave advances air can be trapped and compressed - in joints in the rock or between breaking wave and the cliff
  • then when wave retreats the compressed air expands again
  • continuous process can weaken joints and cracks in the cliff - causing pieces of rock to break off
  • force of breaking wave can also hammer a rock surface
  • at high velocities where bubbles form in the water and them collapse they erode by hammer-like pressure effects
• corrosion -

  • cliffs formed from alkaline rock (eg chalk or limestone) or an alkaline cement bonds the rock particles together solution by weak acids in seawater can dissolve them
• attrition -

  • gradual wearing down of rock particles by impact and abrasion as the pieces of rock are moved by waves, tides and currents
  • process gradually reduces particle size and makes stones rounder and smoother