First 242 words of the document:
A delta is usually composed of fine sediment which is deposited when a river loses energy
and competence as it flows into an area of slowmoving water such as a lake or the sea.
When rivers like the Mississipi or the Nile reach the sea, the meeting of fresh and salt water
produces an electric charge which causes clay particles to coagulate and to settle on the sea
bed, a process called flocculation.
The finest materials are carried furthest and form the bottom of the sea beds. These will be
covered by slightly coarser materials which are deposited to form a slope and make up the
forest beds. The upper layers, nearest to the land and composed of still coarser deposits are
the horizontal topset beds.
Deltas are so called because it was thought that their shape resembled that of delta, the
fourth letter of the Greek alphabet. Geomorphologists have categorised the three different
basic shapes of deltas.
Arcuate: having a rounded, convex outer margin e.g. the Nile.
Cuspate: where the material brought down by a river is spread out evenly on either ide of its
channel, e.g. the Tiber.
Bird's Foot: where the river have many distributaries bounded by sediment and which
extend out to sea like the claws of a birds foot, e.g. the Mississippi