Coasts

• Littoral Zone

  Area of shoreline where land is subject to wave action
• Littoral Zone Subdivisions

  - Offshore

  - Nearshore

  - Foreshore

  - Backshore

  - Beach
• Offshore

  Where waves begin to break in the deeper water. Friction between the waves and the sea bed may cause some distortion of the wave shape.
• Nearshore

  Friction between the seabed and waves distorts the wave sufficiently to cause it to break.

  Possible breakpoint bar formation.
• Foreshore

  The area between the high tide and the low tide mark.
• Backshore

  The area above the high tide mark, affected by wave action only during major storm events.
• Why are Littoral zones dynamic zones of rapid change?

  Short term - Changing inputs, through flows and outputs of energy and material. High and low tide variation, wave energy due to weather.

  Long term - Sea level variation due to climate change
• Classifying Coasts - Long Term Criteria (2)

  - Geology

  - Sea Level Change
• Classifying Coasts - Geology

  - Characteristics of land, including lithology (rock type) and structure (arrangement of rock units).

  - Used to classify coasts as cliffed, sandy, estuarine, concordant and discordant
• Cliffed Coastline (4)

  - High energy environment

  - Rate of Erosion exceeds Deposition.

  - High relief varying from a few meters to hundreds of meters

  - Resistant Geology
• Sandy Coastline (5)

  - Low Relief with Sand Dunes and Beaches

  - Less Resistant Geology

  - Low energy environment

  - Rate of Deposition exceeds Erosion

  - Constructive waves
• Estuarine Coastline (5)

  - Low Relief with Salt Marshes and Mudflats

  - Form in River Mouths

  - Low energy environment

  - Rate of Deposition exceeds Erosion

  - Less Resistant Geology
• Classifying Coasts - Sea Level Change

  - Used to Classify Coasts as Emergent or Submergent

  - Caused by eustatic/isostatic changes

  - Caused by climate change
• Climate Change caused by Cycles

  - Sea Levels rise and fall in 100,000 year cycles

  - Due to Earths Orbit

  - Falls for 90,000 years as ice sheets expand

  - Rises for 10,000 years during interglacial periods

  - Rises when all surface ice melts
• Emergent Coastline


  As Sea Levels fall, coastline land is exposed which was previously covered by the sea
• Submergent Coastline


  As Sea Levels rise, the land is covered
• Concordant Coastline


  - Alternating bands of rock that run parallel to the coastline

  - Also called Dalmatian Coasts
• Discordant Coastline


  - Alternating bands of rock that run at 90 degrees to the coastline

  - Also called Atlantic Coasts
• Classifying Coasts - Short Term Criteria (3)

  - Energy Inputs

  - Sediment Inputs

  - Advancing/Retreating
• Classifying Coasts - Energy Inputs (5)

  - Used to classify High/Low Energy Coastlines

  - Waves (Main Input)

  - Tides (Moon's Gravitational Pull)

  - Currents

  - Rivers
• Classifying Coasts - Sediment Inputs

  - Sediment is added through deposition and removed through erosion

  - Sediment Inputs received by waves and wind, tides, currents, mass movement and tectonic processes
• Classifying Coasts - Advancing/Retreating


  - Classified as Advancing/Retreating due to processes

  - Long Term Processes = Emergent/Submergent Coastline

  - Short Term Processes = Eroding/Outbuilding Coastline
• Outbuilding Coastline


  - Erosion < Deposition

  - Net gain of sediment

  - Coastline advances
• Eroding Coastline


  - Erosion > Deposition

  - Net loss of sediment

  - Coastline retreats
• Cliffed Coasts - UK

  - Occupy 1,000km of UK coastline

  - Mainly located in North and West

  - High relief = 427m (Conachair Cliff, Isle of Hirtha)

  - Low Relief = 3m (Chappel Porth, Cornwall)
• Weathering


  Breakdown of rock in situ, and may be a mechanical, biological or chemical process.
• Erosion


  Wearing away of land due to wave action
• Mass movement


  Downslope movement of material due to the force of gravity.
• Formation of Coastal Plains

  - Formed by Coastal Accretion (Continuous net deposition causes coastline to extend seawards)

  - Can extend biologically if plants colonise shallow water, trapping sediment
• Where does Coastal Accretion come from? (2)

  - Offshore sources (transported by waves, currents and tides)

  - Terrestrial sources (transported by rivers, glaciers, wind or mass movement)
• Dynamic Equalibrium


  - When Erosion = Deposition

  - Continuous flows of energy and material through the coast but size of stores remains unchanged
• Concordant coastline - Lulworth Cove


  - Resistant Portland Limestone forms a protective stratum layer parallel to sea.

  - Less Resistant Purbeck Limestone and Wealden Clay lie behind the Portland Limestone.

  - Portland limestone erodes very slowly, retreating landwards by marine undercutting.

  - At points where Portland Limestone is weaker, erosion managed to break through leading to the erosion of the less resistant Purback Limestone and Wealden Clay. This is done by lateral erosion.

  - Destructive waves have a stronger backwash so material is dragged out the cove. This can cause small beaches.

  - Waves continue to erode Portland Limestone. Attrition and abrasion are responsible for the erosion and the cove is widened more and more.
• Concordant Coastline - Croatia

  - Dalmatian coastline on the Adriatic Sea (Croatia in particular)

  - Formed where the geological structure consists of folds parallel to the coastline

  - Folded Ridges (Anticlines) and Down Folded Valleys (Synclines) are aligned parallel to the coast

  - Sea Level rise at the end of the Devensian glacial period caused flooding of Synclines

  - This produced narrow islands parallel to the coast that are seperated by narrow sea channels
• Concordant Coastline - Haff Coastline


  - Formed when deposition produced unconsolidated geological structures parallel to the coastline

  - During Devesian Ice age, sea levels were 100m lower than today

  - Thick layers of sand and gravel deposited by meltwater rivers

  - Holocene interglacial constructive waves moved the deposited sediment landwards as sea levels rose

  - Bars formed across bays and river mouthes, causing lagoons to be formed behind the bar (East of Gdansk)
• Discordant coastline - Swanage Bay


  - Isle of Purbeck in East Dorset

  - The waves erode the less resistant Wealden Clay which eventually forms a bay, where wave energy is low.

  - More resistant rock is resistant to erosion, so sticks out and forms a headland, where the wave energy is high.

  - Jurassic Portland Limestone forms a headland extending 1km out into sea

  - Resistant Cretaceous chalk forms another headland extending 2.5km out into the sea

  - As the waves approach the headland, it absorbs wave power and refracts - meaning they change motion and direction around the headland.

  - After the wave hits the headland, it is likely to become a constructive wave. These waves carry material and deposit it as swash is more powerful than backwash.

  - The bay will eventually come forwards and become a beach, whilst the headlands are slowly eroded by hydraulic action.

  - The coastline eventually becomes smooth until the process repeats.
• Geological Structure


  Characteristics and arrangement of rock units.
• Strata


  Different layers (or beds) of rock.
• Bedding Plane


  Surface separating layers of strata.
• Deformation


  Degree of tilting of folding of rock.
• Dip


  Angle of inclination of titled strata.