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At the final course of a river, when it enters the sea, it mixes with the surrounding water, and its velocity of flow is checked, causing it to deposit its load of gravel, sand, silt and clay. The first materials deposited are the gravel and sand, as they are by far the heaviest and coarsest. Next to be dropped is the silt. Because it is fine, the clay is transported in suspension quite far out in the sea. When salt water causes the clay to flocculate, it becomes heavier and sinks. As layers upon layers of alluvial materials are deposited, a platform of alluvium is built up and it eventually rises above the water, which can now be called the delta. The water then overflows the banks into different channels called distributaries, which build up their own levees. The vegetation that later grows on the alluvium stabilizes the delta.
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 RiverThe Nile ( Arabic: an-nil , in Africa, is one of the two longest rivers on Earth. Whether the Nile is longer than South America's Amazon still remains the subject of much debate. This is, for the most part, due to two reasons: first, the lengths of rivers, 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) letter deltaDelta (upper case Δ, lower case δ) is the 4th letter of the Greek alphabet. In the system of Greek numerals it has a value of 4. A river delta is named after the letter delta because it has roughly the triangular shape of the upper-case delta. (Δ). Other rivers with notable deltas include the GangesThe River Ganges Ganga in Indian languages) is a major river in northern India. It originates as the Bhagirathi from the Gangotri Glacier in the Uttaranchal Himalayas and joins the Alaknanda near Deoprayag to form the Ganga. Then on, the Ganga flows acros/ BrahmaputraThe Brahmaputra is one of the major rivers of Asia. In Sanskrit, it means "son of Brahma". It originates in the Himalayan mountains in western Tibet, in China and flows 2900km into the sea in the Bay of Bengal in Bangladesh. It is called Tsangpo in Tibet combination (this delta spans most of BangladeshThe People's Republic of Bangladesh is a country in South Asia that forms the eastern part of the ancient region of Bengal. Bangladesh literally means "The Country of Bengal". Lying north of the Bay of Bengal, on land it borders India almost exclusively,), the NigerThe Niger River is the principal river of western Africa, extending over 2500 miles (about 4000 km). It runs in a crescent through Guinea, Mali, Niger, Benin and Nigeria, discharging through a massive delta, known as the Oil Rivers, into the Gulf of Guine, the Amazon, the Mississippi, the Rhine, the Rhône, the Danube, the Mekong, and the Ebre.