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
- The sediment load is very large
- The following conditions are likely to be met
- 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.
- Occurs as fresh water mixes together with salt water.
- 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
- THE LARGER AND HEAVIER PARTICLES - The first to be deposited as the river loses its energy
- 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.
- Arcuate delta e.g. Nile Delta
- Where are deltas located and why are they found here?
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