AS Physical Geography

Page 1

Deltas are features found where rivers that contain much sediment flow into the sea; velocity is reduced and so deposition of material occurs.

Not all rivers have deltas at their mouths, and their size and shape vary greatly.

There are three different types of deltas:

1. Arcuate: Rounded, convex edges. For example the Nile.

2. Cuspate: Material evenly spread from the river. For example the River Ebro in Spain.

3. Birds foot: Spread over a wide area with many 'distributaries' extending out to sea. For example the Mississippi.

Deltas

Deltas build up in time and three beds can be observed:

Bottom set: This has the finest material, which is carried furthest in suspension and sinks to the sea bed.

Foreset: More rapidly deposited, coarser material. Builds out to sea.

Topset: Deposits from river with the most coarse material.

There are different factors influencing the formation of deltas:

Amount of sediment available.

Variations in volume of water discharges from thew river.

Aspect and geometry of the coast.

Coastal processes in operation, for example, wave action.

Changes in coast level.

Impacts of climate on growth of vegetation and marine organisms.

Deltas