Delta’s

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power point done for class on the formation of deltas

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Delta’s

  1. 1. Depositional Fluvial Landforms<br />Delta’s<br />
  2. 2. A delta is a feature of deposition formed when a river flows into a standing body of water <br />Deposition occurs as the velocity drops on entering the standing body of water, this reducing the capacity and competence of the river  bedload and suspended material are ‘dumped’<br />Delta’s<br />
  3. 3. Delta’s form when velocity drops as the river enters a standing body of water, typically this is at the coast as the river flows into the sea<br />Delta’s<br />An example of a delta formed when a river flows into the sea in south west Greenland<br />
  4. 4. Flocculation occurs as fresh water mixes with salt water - e.g where a river flows into the sea -(then called brackish water), and is the process by which tiny particles in suspension like clay and silt (which under normal fresh water conditions would likely never fall out of suspension) coagulate with the salt in the water by chemical reaction and become heavy enough to ‘sink’ and be deposited <br />Flocculation <br />
  5. 5. Deltas only form where rate of deposition exceeds rate of sediment removal – i.e. Where the critical threshold is no longer met and the system has fallen out of dynamic equilibrium. These conditions are likely where:<br />The calibre of the load of the river is very large (therefore requiring a high amount of energy to keep in transport)<br />The costal area into which the river dumps its load has a small tidal range and weak currents  meaning there is limited wave action and therefore little subsequent transport of sediment taking place after its initial deposition allowing large deltas to form<br />Typical conditions for a Delta<br />
  6. 6. Delta’s are usually composed of three types of deposit<br />Topset beds: The larger and heavier particles are the first to be deposited as the river looses energy<br />Foreset beds: Medium calibre particles travel a little further before they are deposited as more steep angled ‘wedges’ of sediment<br />Bottomset Beds: The very finest particles travel the furthest before very low velocity/flocculation leads to their deposition <br />Composition of Delta’s<br />
  7. 7. Composition of Delta’s<br />
  8. 8. Delta’s can be categorised into three main shapes<br />Arcuate <br />Birds Foot <br />Cuspate<br />Types of Delta<br />
  9. 9. Arcuate Delta’s<br /><ul><li>The most common shape of delta
  10. 10. Characteristics: curving shoreline (smoothed by long shore drift), distinct pattern of drainage (branching of distributaries), and typically more ‘gravely’ deposits .
  11. 11. Example: the Nile Delta </li></li></ul><li>Birds Foot Delta<br /><ul><li>‘Fingers’ of deposition build out into the sea along the distributaries channels giving an appearance like a birds claw. Typically with a finer sediment
  12. 12. Example: the Mississippi delta</li></li></ul><li><ul><li>A cuspate delta is shaped like a tooth by gentle but regular opposing currents in the water body the river flows into, or longshoredrift
  13. 13. Example: The river Ebro delta in Spain</li></ul>Cuspate Delta<br />
  14. 14. Web:<br />Image [slide 3]: http://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/NarsarsuaqGreenland-ArcuateDelta.jpg/380px-NarsarsuaqGreenland-ArcuateDelta.jpg<br />Image [slide 10] : http://strata.geol.sc.edu/MARINESEDIMENTS/delta/Nile.jpg<br />Image [slide 11]:http://www.es.ucsc.edu/~es10/classnotes/images/MississippiDelta.drawn.jpg<br />Image [slide 12]:http://www.iberianature.com/material/photos/google_earth_spain_2/images/delta_de_ebro.jpg<br />Info:http://wiki.answers.com/Q/Examples_of_cuspate_deltas<br />Books: AQA text book, Oxford dictionary of Geography<br />Bibliography <br />
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