What is a Delta and How is it Made?
If we look at the map of Egypt, we shall find the Nile, which is a very good example of a river with a delta at its mouth, and we shall notice how the river, when it meets the a, spreads out into a shape something like a triangle. Now that is the shape of the Greek capital letter D, the name for which is delta; and so land of this shape and origin made at the mouth of some rivers is called a river delta.
A river consists of moving water, and the motion of the water has power to rub away m the bed and the banks of the river a large quantity of solid material. This is not melted or dissolved in the river water, but is carried down by it. Now, when the river water meets the sea, its pace slackens, because it is opposed by the weight of the sea water. The solid matter held in the river water is likely to sink and form a wide bed or bank of mud.
Deltas are nearly always found at the mouths of rivers that flow into lakes or into closed seas or sheltered gulfs, because these seas and lakes do not have strong currents or tides to carry away the solid matter. Deltas grow quite fast. The Mississippi River is depositing so much solid matter (sediment) at its mouth that the shore line is moving into the Gulf of Mexico a mile in about sixteen years.
