Download - Delta
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Depositional Fluvial Landforms
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A delta is a Depositional Fluvial Landform inhumid geomorphic region except for Nile delta ofEgypt which is in arid region.
A delta is a feature of deposition formed when a riverflows into a standing body of water.
Deposition occurs as the velocity drops on entering thestanding body of water, this reducing the capacity andcompetence of the river bed load and suspendedmaterial are ‘dumped’.
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Delta forms 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.
An example of a delta formed when a river flows into the sea in south west Greenland
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Flocculation occurs as fresh water mixes with saltwater- e.g where a river flows into the sea -(then calledbrackish water), and is the process by which tinyparticles in suspension like clay and silt (whichunder normal fresh water conditions would likelynever fall out of suspension) coagulate with the salt inthe water by chemical reaction and become heavyenough to ‘sink’ and be deposited.
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Delta is a site of deposition
Formation of a delta depends on the estuarine dynamics
It also depends on the velocity of river
In long term processes size & shape of a delta depends on rock characteristics, rate of erosion, rate of rainfall in the upper river basin and in the ways river flwos.
Singh, S, 2005
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Deltas only form where rate of deposition exceeds rate of sediment removal. These conditions are likely where:
The calibre of the load of the river is very large (therefore requiring a high amount of energy to keep in transport).
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
Suitable place in the form of shallow sea or lake shores
Long courses of river; means long river system
Relatively calm seaSingh, S, 2005
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Accelerated rate of erosion in the catchment area of the river
Large amount of sediment supply
Geologically inactive sea coast; means almost stable condition of sea bottom
Singh, S, 2005
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Hyperpycual: The density of river water is greater than the sea water
Homopycual: The density of river water is same as the sea water
Hypopycual: The density of river water is less than the sea water
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Delta is a very complex depositional system including three morphological process i.e. fluvial, terrestrial and marine environment.
Delta’s are usually composed of three types of deposit
Topset beds: The larger and heavier particles are the first to be deposited as the river looses energy
Foreset beds: Medium calibre particles travel a little further before they are deposited as more steep angled ‘wedges’ of sediment
Bottomset Beds: The very finest particles travel the furthest before very low velocity/flocculation leads to their deposition
Singh, S, 2005
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Classification of delta by dominance Wave dominated delta –i.e. Nile delta, Egypt
Tide dominated delta –i.e. Ganges delta, Bangladesh, India
Estuarine dominated delta –i.e. Mackenzia, Hudson delta
Classification of delta by shape Arcuate –i.e. Ganges delta, Nile delta
Birds Foot –i.e. Mississippi delta
Cuspate –i.e. Ebro delta in Spain
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Delta type:Arcuate deltaTide dominated delta
http://eol.jsc.nasa.gov/debrief/STS066/rep2.htm
Ganges Delta, Bangladesh
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NASA satellite image in false color
Nile Delta, Egypt
Delta type:Wave dominated delta Arcuate delta
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http://earthobservatory.nasa.gov/IOTD/view.php?id=50500
River Deltas, Lake Ayakum, Tibet
Delta type:Arcuate delta
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Mississippi Delta
Delta type:Birds Foot
Jesse Allen, University of Maryland’s Global Land Cover Facility, andLANDSAT 1
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Okavango Delta, Botswana
Delta type:Arcuate deltaTide dominated delta
http://www.flickr.com/people/8942661@N02
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Colorado River Dry Delta
http://gallery.usgs.gov/photos/10_15_2010_rvm8Pdc55J_10_15_2010_0#.Ur0mcvfTnrd
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Web: Image [slide 12]: http://eol.jsc.nasa.gov/debrief/STS066/rep2.htm
Image [slide 13] : NASA satellite image in false color
Image [slide 13]: http://earthobservatory.nasa.gov/IOTD/view.php?id=50500
Image [slide 14]: Jesse Allen, University of Maryland’s Global Land Cover Facility,
andLANDSAT 1
Image [slide 15]: http://www.flickr.com/people/8942661@N02
Image [slide 16]: http://gallery.usgs.gov/photos/10_15_2010_rvm8Pdc55J_10_15_2010_0#.Ur0mcvfTnrd
Info: www.wikipedia .com
www.slideshare.com
Books: Singh, S; Geomorphology, Prayag PustakBhawan, 2005
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Thank You