How are deltas formed?

Refers to AQA AS Geography (Chapter 1 - Rivers, floods and management)

  • Created by: Bethany
  • Created on: 09-05-13 10:22
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  • Formation of Deltas
    • Where are deltas located and why are they found here?
      • At the mouth of a river as it enters a sea or lake.
      • The deposition occurs here due to the velocity and sediment-carrying capacity of the river decreasing on its enterence to the lake or sea.
        • bedload and suspended material are dumped.
      • Can only be found when the rate of deposition EXCEEDS the rate of sediment removal.
        • The following conditions are likely to be met
          • The sediment load is very large
            • Mississippi River
            • Nile River
          • The coastal area into which the river empties its load has a small tidal range/ weak currents. There is limitied wave action so there is little transportation of sediment after deposition has taken place.
            • Gulf of Mexico
            • Mediterranean Sea
    • What is flocculation?
      • Occurs as fresh water mixes together with salt water.
        • Clay particles coaggulate due to a chemical reaction
        • Causes clay to settle on the river bed.
    • What are the three types of deposit that deltas are usually composed off?
      • THE LARGER AND HEAVIER PARTICLES - The first to be deposited as the river loses its energy
        • Form TOPSET BEDS
      • THE MEDIUM GRADED PARTICLES - Travel a little further before they are deposited as steep-angled wedges of sediment.
        • Form the FORESET BEDS
      • THE VERY FINEST PARTICLES - Travel furthest into lake before being deposition.
        • Form the BOTTOMSET BEDS
    • What shapes can characterise a delta?
      • Arcuate delta e.g. Nile Delta
        • Curving Shoreline
        • Mant tribuataries break away from the main channel as deposition within the channel itself occurs
        • Longshore drift keeps the seaward edge of the delta fairly smooth
      • Birdsfoot delta e.g Mississipi
        • Fingers of deposition along distribuatires' channels, giving 'birds claw' appearence.
      • Cuspate delta
        • Pointed like a cup or tooth
        • Shaped by gentle, regular, but opposing sea currents/ longshore drift.


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