Costal landscape + change

• Costal plain = land which gradually slopes down towards the sea.

  Sand dunes and mud flats are common here.
• Strata = the different layers of rock within an area and how they relate to each other

  
• Deformation = the degree to which rock units have been deformed (tilted or folded) by tectonic activity
• Faulting = major fractures that have moved rocks from their original position
• Geological structure produces two dominant types of coasts:

  • Concordant: when rocks run parallel to the coastline
  • Discordant: when different rock strata interest the coast at an angle, creating varied geology (headlands and bays common)
• Faults = major weaknesses within rock layers. Physical weathering makes this worse
• Joints = occur in most rocks, dividing rock strata up into blocks
• Fissures = smaller cracks in rocks which represent weaknesses in the rock (erosion/weathering then occurs)
• Igneous (granite, basalt and dolerite)

  • V slow erosion rate
  • Crystalline rocks - interlocking crystals make it strong
  • Granite and others have few joints so less areas of weakness
• Metamorphic (slate and marble)

  • Slow
  • Crystals are all orientated in one direction which produces weaknesses
  • Often folded and heavily fractured
• Sedimentary (sandstone, limestone and shale)

  • Medium -> fast
  • geologically young rocks so weaker
  • Has many fractures and bedding planes
  • many allow water to flow through them
• Unconsolidated sediment (sand, clay and silt)

  • Not compacted to become sedimentary rock
  • Easily eroded
• waves

  • potential energy of a wave is proportional to its height
  • friction from sand causes the height to increase and the wavelength to decrease

  
• Destructive waves:

  • frequent (13-15 waves / min)
  • strong backwash
  • has a deeper nearshore so more energy carried through

  
• Constructive waves:

  • nearshore is shallower with gently sloping sand beaches which reduces wave energy
  • waves are elliptical giving it a strong forward motion
  • swash is strong
  • less frequent (6-8 /min)

  
• Attrition: rocks and pebbles hitting each other, eroding them
• Abrasion: destructive waves chuck sand / pebbles at rocks
• Hydraulic action: large destructive waves act on rocks, which can cause compressed air into the rocks. The sudden pressure can crack them
• Wave cut notch:

  • at high tide, destructive waves reach base of cliff
  • abrasion and hydraulic action act on it
  • causes wave cut notch and sometimes caves
• Cliff retreat:

  rock above a wave cut platform is unsupported and can collapse

  weathering can also accelerate this

  
• Sediment cells:

  • Has sources, transfers and sinks.
  • theoretically a closed system
  • erosion in one place (source) causes deposition in others (sinks)
  • the sediment budget is sediment from sources and that lost to sinks

  
• Dynamic Equilibrium:

  • Negative feedback = tends to maintain equilibrium, e.g. when wave erosion causes rock fall which then protects the cliff base from further erosion
  • Positive feedback = increases change in system e.g. wind blowing on sand dune can cause further erosion and more vegetation loss
• Mechanical weathering:

  • Salt crystallisation = when sea water splashes on rock, and sodium + Mg salt compounds enter joints and cracks them
  • freeze thaw = water gets into cracks, freezes, expands and forces rocks apart
• Chemical weathering:

  • Oxidation = O2 + Fe in rocks causes chemical breakdown of minerals. Results in lack of bondage so crumbles
  • Carbonation = when CO2 + H2O reacts and makes an acid, causing it to corrode (carbonic acid) affects limestone
• Biological weathering:

  • Growing vegetation = when roots enter the rocks and slowly break apart the rock. It can be mixed with freeze thaw too.
  • seaweed = contains sulphuric acid, which can be released and cause chemical weathering (carbonation)
• Rotational slumping = when a section of a cliff (remaining intact) goes down a cliff. This leaves behind a rotational scar.

  common in unconsilidated sediment like clay

  
• Eustatic change = change in sea level relative to land. Caused by melting ice. Risen by 120m in 10,000 years
• Isostatic change = change in land level relative to sea level. In glacial period, the north was pushed down which rose the south. Now it’s rebounding (north) and much sediment in deposited in the south further sinking it
• Tectonic change = as plates move, continental shelves and land are pushed upwards. Volcanos can create new islands but tsunamis can flood coasts
• Climate change + sea level rise:

  • thermal expansion occurs, increasing the volume of water (contributes to 50%> of sea level rise)
  • melting glaciers shall add to sea level rise
  • sea level rise of 2m expected by 2100
  • erosion rates intensified by sea level rise
• Human action + sea level rise:

  • changes sediment cells
  • e.g. Groynes cause terminal Groyne Syndrome
  • dredging offshore removes sand which reduces wave friction. Also can cause narrower beaches (Hallsands)
• Lithology = rock type

  geology = characteristics of the land (Faults, jointing

  ,etc )
• Factors affecting flood risks:

  • Height - low lying land at risk of being flooded (Kiribati)
  • Areas experiencing is isostatic sinking.
  • vegetation removal like bubring mangroves for fuel
• Mangroves mitigate costal flooding by:

  • reduce the height of the wave, reducing erosion on coast (energy is proportional to height of wave)
  • their roots trap sediment, increasing the height of the land
  • they reduce storm surge levels
• Hard engineering:

  • Groynes- increase size of beach, increased likelihood of more tourism, not ugly. However, cost £1000/m, causes terminal groyne syndrome
• Hard engineering:

  • Sea walls - effectively stops erosion, prevents water inland, gives a sense of security. However, £5000/m, looks ugly
• Hard engineering:

  • Rip rap (boulders w/ large surface area to dissipate waves) - long lasting, can be placed at vulnerable points like base of sea wall. However, costs £50/m^3, looks ugly, water can still pass through
• Hard engineering:

  • Revetments (sloped walls in front of the back shore reduces the force of them)- absorbs wave energy and traps sediment, long shore drift can continue. However, £1500/m, constant maintenance.

  
• Hard engineering:

  • Offshore breakwaters (boulders dropped parallel to shore. Dissipates waves) Longshore drift continues behind them, can create water areas behind for water sports. However, costs £1-2m, other defences may be needed

  
• Soft engineering:

  • Beach nourishment. Looks natural, supports tourism industry. however, costs £10/m^3, may have to be rebuilt after storms (slapton), dredging to get sand can cause future problems (hall sands)