coasts

• what are the factors that make coasts natural systems


  they have:

  -inputs

  -outputs

  -flows/transfers

  -stores/components
• what is input and output

  input=sediment can be brought into the system-wind, waves, tides and currents

  
  

  outputs: sediment can be washed out to sea or deposited further along the coast
• what are flows and stores

  flows/transfers= erosion, weathering, transportation, deposition

  
  

  stores/components= landforms-beaches, dunes, spits
• what is an example of negative feedback at the coast


  as a beach is eroded, the cliffs behind it are exposed to wave attack

  sediment eroded from the cliffs is deposited back on the beach-causing it to grow in size again
• what is an example of positive feedback at the coast


  as a beach starts to form it slows down waves, which causes more sediment to be deposited-increasing the size of the beach

  new equilibrium is reached when long term growth of the beach stops
• what are the sources of energy in coastal systems


  -wind

  -waves

  -tides

  -currents
• how is the wind an input of energy at the coast


  air moving from areas of high pressure to areas of low pressure

  
  

  during storms the pressure gradient is high=winds are strong

  
  

  strong winds=generate powerful waves-some areas wind consistently blows from same direction=prevailing wind=higher-energy waves
• how are waves an input of energy at the coast


  created by wind=friction gives circular motion

  effect on shore=height dependant

  wave height impacted by wind speed+ fetch

  
  

  high wind speed+ long fetch=higher more powerful waves

  break when get to shore-friction with sea bed-slows bottom=more elliptical=crest rises and collapses

  swash=onto shore

  backwash=moving back toward sea
• what are constructive waves


  low frequency 6-8 per min

  
  

  low + long- more elliptical cross profile

  
  

  powerful swash carries carries material-deposits-low energy
• what are destructive waves


  high and steep

  
  

  circular cross profile

  
  

  higher frequency 10-14 per min

  
  

  strong backwash erodes the beach- high energy
• how are tides an input of energy at the coast


  the periodic rise + fall of the ocean surface-caused by gravitational pull of the moon and the sun

  
  

  affect position waves break on the beach

  
  

  the area of land between max high tide and min low tide is where most landforms are created + destroyed
• how are currents an energy input at the coast


  general flow of water in one direction

  
  

  caused by wind, variations in water temps and salinity

  
  

  move material along the coast
• what are high energy coasts

  receive high inputs of energy=large powerful waves

  caused by: strong winds, long fetches, steeply shelving off shore zones

  
  

  sandy coves + rocky landforms( cliffs caves stacks arches)

  
  

  rate of erosion>rate of deposition
• what are low energy coasts


  low inputs of energy=small, gentle waves

  
  

  short fetches+ gently sloping offshore zones

  
  

  due to reef or island offshore-protects coast from waves

  
  

  saltmarshes + tidal mudflats

  
  

  rate of deposition>rate of erosion
• what are the inputs of sediment into the coastal system


  -rivers

  -sea level rise-forms estuaries

  -eroded from cliffs

  -from crushed shells

  -offshore deposits(sandbanks)
• what is a sediment budget


  the difference between the amount of sediment that enters a system and the amount that leaves
• what are sediment cells


  also littoral cells

  
  

  lengths of coastline-between headlands- self-contained for movement of sediment

  
  

  processes in one cell dose not affect another

  
  

  each cell is a closed coastal system
• what are the 6 ways of eroding a coastline


  -abrasion

  -hydraulic action

  -cavitation

  -wave quarrying

  -solution

  -attrition
• what is transportation and what are the 4 main processes


  the process of eroded material being moved

  -solution

  -suspension

  -saltation

  -traction
• what is longshore drift


  swash carries sediment up the beach, in direction of prevailing winds

  backwash carries sediment back down beach at right angles to sea

  this moves sediment along the coastline
• what is deposition, and what are the two types


  the process of dropping eroded material

  
  

  marine-seawater

  aeolian-wind
• when does this deposition happen


  sediment load exceeds ability of wind/water to carry it

  if sediment load increase-water/wind flow slows down(less energy)
• why do wind and water slow down


  friction increases=shallow or reaches land

  
  

  flow becomes turbulent= encounters obstacle-flow is rougher+ speed decreases

  
  

  if wind drops wave height speed + energy will decrease as well
• what is sub- aerial weathering


  gradual breakdown of rock by ice, salt, plant roots and acids- weakens cliff= more vulnerable to erosion
• what is mechanical weathering and give an example


  to do with climate and pressure

  
  

  freeze-thaw

  temps fluctuate above and below freezing

  water enters joints and crevices

  temp drops below 0C, water freezes and expands

  over time repeated freeze thaw action weakens the rocks and causes pieces to fall off
• what is chemical weathering and give an example


  breakdown of rocks =changing chemical composition

  carbonation

  co2 in atmosphere dissolves in rainwater= weak carbonic acid

  acid reacts with rock that contains calcium carbonate- rocks are gradually dissolved(limestone)
• what is biological weathering

  vegetation and coastal organisms
• what is salt weathering


  caused by saline water

  
  

  saline water enters pores or cracks in rocks at high tide

  as tide goes out the rocks dry and the water evaporates forming salt crystals

  as salt crystals form they expand-exerting pressure on this rock=pieces fall off
• what is wetting and drying

  some rocks contain clay

  when clay get wet it expands, and the pressure caused by this breaks fragments off the rock
• what is mass movement


  when material moves down a slope- due to gravity

  
  

  in coastal areas its most likely to occur when cliffs are undercut by wave action- unsupported overhang- likely to collapse
• what are the types of mass movement


  -slides=shifts in straight line

  -slumps-shifts with a rotation

  -rockfalls=breaks up and falls

  -mudflows=flows downslope

  also gradual by soil creep
• where/when does mass movement occur


  -unconsolidated rocks-little friction to hold them together

  
  

  -heavy rain-saturates-reduces friction

  
  

  -runoff-erode fine particles + transport them downslope
• what are the coastal landforms caused by erosion


  -cliffs

  -wave-cut platforms

  -headlands+ bays

  -caves, arches + stacks
• how are cliffs formed and wave cut platforms


  sea erodes the land-over time cliffs retreat due to the action of waves and weathering

  
  

  this causes a notch to form at the high tide water mark-develops into a cave- rock above becomes unstable-collapses

  wcp- flat surfaces left behind when a cliff is eroded
• how are headlands and bays formed

  bands of alternating less resistant and more resistant rock at right angles to the shoreline

  
  

  softer rock eroded quickly- forming a bay. harder rock eroded less=headland
• how do caves, arches and stacks form


  cliff profile features

  weak joints/fissures eroded to form caves

  erosion through cause arch when arch collapses it forms a stack- the foreland
• what are the coastal landforms caused by deposition?


  -beaches

  -spits

  -offshore bars and tomolos

  -barrier islands

  -sand dunes

  -estuarine mudflats and saltmarshes
• How are beaches formed?


  -constructive waves deposit sediment on shores=a store in coastal system

  -shingle beaches=steep+narrow-larger particles-which pile up at steep angles

  -sand beaches-formed from smaller particles=wide and flat

  -have distinctive features-berms are ridges of sand +pebbles found at high tide mark

  -runnels are grooves in sand running parallel to shore-formed by backwash draining to the sea

  -cusps= crescent-shaped indentations that form on beaches of mixed sand+shingle
• How are spits formed?


  -form where coast suddenly changes direction-across river mouths

  -longshore drift continues to deposit material across river mouth-leaving bank of sand+shingle sticking out to sea

  -a straight spot that grows out roughly parrellel to the coast= simple split

  -occasional changes to dominant wind + wave direction may lead to a spit having curved end=recurved end

  -over time several recurved ends abandoned as waves return to original direction

  -a spit that has multiple recurved ends from several periods of growth=compound spit

  -area behind spit is sheltered from waves+ often develops into mudflats+saltmarshes
• How are offshore bars and tombolos formed?


  -bars formed when spit joins two headlands together

  -occurs across a bay or river mouth

  -a lagoon forms behind the bar

  -bars also form off the coast when material moves towards the coast-normally as sea level rises-may remain partly submerged by sea=offshore bars

  -bars connects the shore to an island=tombolo

  - Kynance cove, St Ninians isle