delta

Click a letter for the index

Or search the encyclopaedia:

 

 

Go

 

Click image to enlarge
River sediments deposited when a river flows into a standing body of water with no strong currents, such as a lake, lagoon, sea, or ocean. A delta is the result of fluvial and marine processes. Deposition is enhanced when water is saline because salty water causes small clay particles to adhere together. Other factors influencing deposition include the type of sediment, local geology, sea-level changes, plant growth, and human impact. Some examples of large deltas are those of the Mississippi, Ganges and Brahmaputra, Rhône, Po, Danube, and Nile rivers. The shape of the Nile delta is like the Greek letter delta or Δ, and gave rise to the name.

The arcuate (arc-shaped) delta of the Nile, found in areas where longshore drift keeps the seaward edge of the delta trimmed and relatively smooth, is only one form of delta. Others include birdfoot (projecting) deltas, where the river brings down enormous amounts of fine silt, as at the Mississippi delta; and tidal (linear) deltas, like that of the Mekong, China, where most of the material is swept to one side by sea currents. Cuspate deltas are pointed, and are shaped by regular opposing, gentle water movement, as seen at the Ebro and Tiber deltas in Italy.

Yellow stands for mineral wealth. Green represents the country's vegetation and natural resources. Red recalls the blood spilt during the liberation struggle. Effective date: 18 April 1980. >>