Geography-Coasts

• Coasts


  • They are Natural Systems
  • They have inputs, outputs, flows and stores of sediment and energy
• INPUTS


  • Sediment can be brought into the system in various ways
  • Energy inputs come from the wind, waves, tides, and currents
• OUTPUTS


  • Sediment can be washed out to sea, or deposited further along the coast
• FLOWS/TRANSERS


  • eg processes such as erosion, weathering, transportation and deposition can move sediment within the system
• STORES COMPONENTS


  • Landforms such as beaches, dunes, and spits
• Dynamic equilibrium-inputs and outputs are balanced


  A change in one causes negative feedbacks that restore the balance of the system
• Negative feedback


  When a change in the system causes other changes that have the opposite effect. E.g. as a beach is eroded, the cliffs behind are exposed to wave attack. Sediment eroded from the cliffs are deposited on the beach, causing it to grow in size again.
• Positive feedback


  Changes the balance of the system, creating a new equilibrium. The change causes other changes that have a similar effect. E.g. as a beach starts to form it slows down waves, which can cause more sediment to be deposited, increasing the size of the beach. The new equilibrium is reached when long term growth of the beach stops
• Sources of Energy in Coastal Systems


  • Air- wind
  • Water-waves, tides, currents
• Wind


  Created by air moving from areas lf high pressure to areas of low pressure. During events such as storms, the pressure gradient is high and winds can be very strong
• Wind


  • Strong winds can generate powerful waves.
  • In some areas wind consistently blows from the same direction (a prevailing wind)- this caused higher energy waves than winds that change direction frequently
• Waves


  • Created by the wind blowing over the surface of the sea
  • The friction between the wind and the surface of the sea gives the wafter a circular motion
• Waves


  • Wave height is affected by the wind speed and the fetch of the wave
  • The fetch is the maxim distance of sea the wind has blown over in creating the waves. A high wind speed and a long fetch create higher and more powerful waves
• Wave breaking


  1. Aa waves approach the shore they break. Friction with the sea bed slows the bottom of the waves and makes their motion more elliptical (squashed and oval-shaped). The crest of the wave rises up and then collapses

  2. Water washing up the beach is called the swash. Water washing back towards the sea is called the backwash
• Constructive waves


  Constructive waves have a low frequency. They're low and long which gives them a more elliptical cross profile. The powerful swash carries material up the beach and deposits it
• Destructive waves


  Destructive waves are high and steep, with a more circular cross profile. They have a higher frequency. The strong backwash removes material from the beach.
• Wave frequency


  It's how many waves pass a point in a particular time
• The waves in an area are usually mainly constructive or mainly destructive
• Tides


  The periodic rise and fall of the ocean surface, caused by the gravitational pull of the Moon and the Sun
• Tides 


  Tides affect the position at which waves break on the beach (at high tide they break higher up the shore). The area of land between maximum high tide and minimum low tide is where most landforms are created and destroyed
• Currents


  • The general flow of water in one direction-it can be caused by wind or by variations in water temperature and salinity
  • They move material along the coast
• High-energy coasts


  • Receive high inputs of energy in the form of large, powerful waves. These can be caused by strong winds, long fetches and steeply shelving offshore zones. High-energy coastlines tend to have sandy caves and rocky landforms, e.g. cliffs, caves, stacks and arches. The rate of erosion is often higher than the rate of deposition
• Low-energy coasts


  • Receive low inputs of energy in the form of small, gentle waves. These can be caused by gentle winds leg. if the location is sheltered, short fetches and gently sloping offshore zones. Some coastlines are low energy because there is a reef or island offshore, which protects the coast from the full power of waves. Low-energy coastlines often have saltmarshes and tidal mudflats. The rate of deposition is often higher than the rate of erosion
• Sediment Sources in Coastal Systems

  • Rivers carry eroded sediment into the coastal system from inland
  • Sea level rise can flood river valleys, forming estuaries. Sediment in the estuary becomes part of the coastal system
  • Sediment is eroded from cliffs by waves, weathering and landslides
  • Sediment can be formed from the crushed shells of marine organisms
  • Waves, tides and currents can transport sediment into the coastal zone from offshore deposits (e.g. sandbanksi
• Sediment budget


  The difference between the amount of sediment that enters the system and the amount that leaves. If more sediment enters than leaves, it's a positive sediment budget and overall the coastline builds outwards. If more sediment leaves than enters, it's a negative sediment budget and overall the coastline retreats
• Sediment cells


  Lengths of coastline loften between two headlands) that are pretty much entirely self-contained for the movement of sediment (.e. sediment doesn't move between cells). This means that processes going on in one cell don't affect the movement of sediment in another cell-each cell is a closed coastal system
• Coastal Processes


  • Erosion
  • Transport
  • Deposition
• Ways Waves Erode the Coastline

  • Hydraulic action
  • Compression
  • Expansion
  • Wave plucking
  • Solution
  • Abrasion
• Processes of Eroded Material Being Moved

  • Suspension
  • Saltation
  • Traction
  • Longshore drift
• Processes of Dropping Eroded Material

  • Marine deposition
  • Aeolian deposition
• Reasons for Deposition


  • Sediment load increases
  • Wind or water flow slows down
• Types of Sub-aerial Weathering

  • Salt weathering
  • Freeze-thaw weathering
  • Chemical weathering
  • Biological weathering
• Types of Mass Movement

  • Landslides
  • Slumping
  • Rockfalls
  • Mudflows
  • Soil creep
• Coastal Landforms Caused by Erosion

  • Cliffs and wave cut platforms
  • Caves, arches and stacks
  • Headlands and bays
• Coastal Landforms Caused by Deposition

  • Beaches
  • Spits
  • Bars
  • Tombolos
  • Dunes
• Cliff profile features


  Landforms found in cliffs, also called coastal landforms
• Formation of caves


  Weak joints in rock are eroded to form caves
• Formation of arches


  Caves on opposite sides of a narrow headland join up to form an arch
• Formation of stacks


  When an arch collapses, it forms a stack
• Caves, arches and stacks are the result of erosion of rock