Delta is a low plain composed of clay, sand, gravel, and other sediments deposited at the mouth of a river. Deltas are named for the Greek letter delta because many of them have a roughly triangular shape. The Greek historian Herodotus first applied the term in the mid-400’s B.C. Deltas form when rivers flow into large bodies of standing water, where their speed and ability to carry sediments are suddenly reduced.
The chief factors that affect the formation of deltas include climate, geological features, river size and flooding patterns, and the strength of ocean waves. Dams and other structures also influence the development of deltas. For example, construction of the Aswan High Dam in Egypt during the 1960’s decreased the amount of sediments that the Nile River carries to its delta. As a result, waves are destroying parts of the Nile Delta.
Deltas have fertile soil that makes them excellent agricultural areas. The rich land of the Mississippi Delta in Louisiana produces fruits, vegetables, and other crops. The Nile Delta has been farmed since ancient times. Some deltas, such as the Irrawaddy Delta in Myanmar and the Mekong Delta in Vietnam, support vast rice fields.
