How delta formed?

Answer 1

Deltas are complex depositary features which are formed at the mouths of rivers. Some major deltas are the Nile delta in Egypt, the Mississippi delta in the USA and the Ganges delta in Bangladesh.

They mainly form because the velocity of a river slows where the fresh water mixes with the salt water of the sea and the reduction of velocity causes sediment carried by the river, the heaviest sediment first.