River delta
A river delta is a landform shaped like a triangle. It is where the mouth of a river flows into an ocean, or even into a desert. It is formed by sediment carried by the river being deposited in the wider mouth. This happens because the water moves less quickly there.
Over time, the delta forms a series of fingers: places where the water flows, and places above water where plants grow. As time passes, these "fingers" change their position. The landform is typical of the tropical rivers of the past as well as the present.
The word "delta" comes from the Greek letter delta, Δ , because the deltas are shaped like the letter. A river delta can cover just a few square miles, or an area of hundreds or thousands of square miles of land.
There have been times in the past when the tropical rivers were larger than today. The South of England was, in the Jurassic period, part of a larger continent. There is today just a remnant of this huge tropical river. The mud from this river is like huge fingers, with gravel between the fingers. This can be seen in quarries where building materials are sorted for sale.[1][2]
The deposition of mud and sand causes an alluvial fan, which is the name given to the phenomenon.[3]
River Delta Media
Lena river delta
A delta forms where a river meets a lake
Sacramento–San Joaquin (California) Delta at flood stage, early March 2009.
Delta lobe switching in the Mississippi Delta,* 4600 yrs BP,* 3500 yrs BP,* 2800 yrs BP,* 1000 yrs BP,* 300 yrs BP,* 500 yrs BP,×* current
Okavango's delta.
The Kokemäki River (Kokemäenjoki) flows through the city of Pori in Satakunta, Finland. Its delta, where the delta islands remain between the distributaries, starts near the centre.
Delta in Ismenius Lacus quadrangle, as seen by THEMIS.
Delta in Lunae Palus quadrangle, as seen by THEMIS.
Other websites
- Louisiana State University Geology - World Deltas
References
- ↑ Orton G.J. & Reading H.G. 1993. Variability of deltaic processes in terms of sediment supply, with particular emphasis on grain size. Sedimentology. 40 (3): 475–512.
- ↑ Anthony, Edward J. 2015. Wave influence in the construction, shaping and destruction of river deltas: A review. Marine Geology 361: 53–78. [1]
- ↑ Boggs, Sam 2006. Principles of sedimentology and stratigraphy (4th ed). Upper Saddle River N.J.: Pearson Prentice Hall. pp. 289–306. ISBN 0131547283