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Nile River delta, as seen from Earth orbit. Photo courtesy of NASA.

A delta is the mouth of a river where it flows into an ocean, sea, desert or lake, building outwards (as a deltaic deposit) from sediment carried by the river and deposited as the water current is dissipated. Deltaic deposits of larger, heavily-laden rivers are characterised by the river channel dividing into multiple streams (distributaries), these divide and come together again to form a maze of active and inactive channels. A related notion is estuary, which is another type of the river mouth.

Delta formation

This arcuate delta has formed on the south-west coastline of Greenland, near Narsarsuaq.

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Where delta formation is river-dominated and less subject to tidal or wave action, a delta may take on a multi-lobed shape which resembles a bird's foot. The Mississippi Delta is an example of this type.

The most famous delta is that of the Nile River, and it is this delta from which the term is derived, because the Nile delta has a very characteristic triangular shape, like the (upper-case) Greek letter delta ( $\Delta$ ). Other rivers with notable deltas include the Ganges/Brahmaputra combination (this delta spans most of Bangladesh and West Bengal), the Niger, the Amazon, the Mississippi, the Sacramento-San Joaquin, the Rhine, the Rhône, the Danube, the Ebro, the Volga, the Lena, the Tigris-Euphrates, the Indus, the Krishna-Godavari, the Kaveri, the Irrawaddy, and the Mekong.

In rare cases the river delta is located inside of a large valley and is called an inverted river delta. Sometimes a river will divide into multiple branches in an inland area, only to rejoin and continue to the sea; such an area is known as an inland delta, and often occur on former lake beds. The Niger Inland Delta is the most famous example; another is the Danube Inland Delta on the Little Alföld. The Okavango Delta is an example of a delta with no outlet to the sea.

List of deltas

External link

Louisiana State University Geology - World Deltas

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 Where delta formation is river-dominated and less subject to [[tide|tidal]] or [[Ocean surface wave|wave]] action, a delta may take on a multi-lobed shape which resembles a [[bird]]'s foot. The [[Mississippi River Delta|Mississippi Delta]] is an example of this type.
 [[Image:Ganges River Delta, Bangladesh, India.jpg|right|200px|thumb|The [[Ganges]] river delta in [[India]] and [[Bangladesh]] is one most fertile regions in the world.]]
-The most famous delta is that of the [[Nile|Nile River]], and it is this delta from which the term is derived, because the Nile delta has a very characteristic [[triangle (geometry)|triangular]] shape, like the (upper-case) [[Greek alphabet|Greek letter]] [[delta (letter)|delta]] (<math>\Delta</math>). Other rivers with notable deltas include the [[Ganges River|Ganges]]/[[Brahmaputra]] combination (this delta spans most of [[Bangladesh]] and [[West Bengal]]), the [[Niger River|Niger]], the [[Amazon River|Amazon]], the [[Mississippi River|Mississippi]], the [[Sacramento River|Sacramento]]-[[San Joaquin River|San Joaquin]], the [[Rhine]], the [[Rhone River|Rh&ocirc;ne]], the [[Danube Delta|Danube]], the [[Ebro]], the [[Volga River|Volga]], the [[Lena River|Lena]], the [[Tigris-Euphrates alluvial salt marsh|Tigris-Euphrates]], the [[Indus River|Indus]], the [[Krishna River|Krishna]]-[[Godavari River|Godavari]], the [[Kaveri River|Kaveri]], the [[Irrawaddy River|Irrawaddy]], and the [[Mekong]].
+The most famous delta is that of the [[Nile|Nile River]], and it is this delta from which the term is derived, because the Nile delta has a very characteristic [[triangle (geometry)|triangular]] shape, like the (upper-case) [[Greek alphabet|Greek letter]] [[delta (letter)|delta]] (<math>\Delta</math>). Other rivers with notable deltas include the [[Ganges River|Ganges]]/[[Brahmaputra]] combination (this delta spans most of [[Bangladesh]] and [[West Bengal]]), the [[Niger River|Niger]], the [[Amazon River|Amazon]], the [[Mississippi River|Mississippi]], the [[Sacramento heleed    River|Sacramento]]-[[San Joaquin River|San Joaquin]], the [[Rhine]], the [[Rhone River|Rh&ocirc;ne]], the [[Danube Delta|Danube]], the [[Ebro]], the [[Volga River|Volga]], the [[Lena River|Lena]], the [[Tigris-Euphrates alluvial salt marsh|Tigris-Euphrates]], the [[Indus River|Indus]], the [[Krishna River|Krishna]]-[[Godavari River|Godavari]], the [[Kaveri River|Kaveri]], the [[Irrawaddy River|Irrawaddy]], and the [[Mekong]].
 In rare cases the river delta is located inside of a large valley and is called an [[inverted river delta]]. Sometimes a river will divide into multiple branches in an inland area, only to rejoin and continue to the sea; such an area is known as an '''inland delta''', and often occur on former lake beds. The [[Niger Inland Delta]] is the most famous example; another is the [[Danube Inland Delta]] on the [[Little Alföld]]. The [[Okavango Delta]] is an example of a delta with no outlet to the sea.