Geoscience Reference
In-Depth Information
Most rivers eventually flow into the sea or a lake, where they deposit sediment which
builds up into a landform known as a delta. The name comes from the Greek letter delta,
Δ, shaped like a triangle or fan, one of the classic shapes a delta can take. Examples of this
type of delta include two of Africa's largest: those at the conclusion of the Niger and Nile
Rivers.
The river provides the sediment that makes up a delta, but there are many other influences
on its shape, including the volume of water flowing, the amount of sediment, and the relat-
ive importance of the flow of the river, the ebb and flow of tides, and the energy of waves.
Fan-shaped deltas like the Niger and Nile are dominated by the action of the waves. Deltas
dominated by the flow of the river typically extend further out into the sea as a lobe, its
channels branching like the toes or claws of a bird. The Mississippi River delta is an ex-
ample of the 'bird-foot delta' type. Tide-dominated deltas form in locations with a large
tidal range or fast tidal currents. They are typified by numerous islands elongated parallel
to the main tidal flow and perpendicular to the shore line. Good examples are the deltas
of the Fly River in New Guinea and the delta at the confluence of the Brahmaputra and
Ganges Rivers.
