13Deltas

Edward J. Anthony

Aix Marseille Université, Institut Universitaire de France, Europôle Méditerranéen de l’Arbois, Aix en Provence Cedex, France

13.1 Deltas: definition, context and environment

13.1.1 A definition of deltas

Wright (1985) defined deltas as subaqueous and subaerial coastal accumulations of river-derived sediments adjacent to, or in close proximity to, the source stream, including the deposits that have been secondarily reworked by waves, currents or tides. Most river deltas are formed on the margins of marine basins, and the deltas of some of the biggest rivers are the largest coastal landforms in the world (Evans, 2012), but deltas exist in all sizes (Fig. 13.1). It is relevant to note at the outset that sediment transported from deltas is important in sourcing adjacent coasts in sediments, both relict and modern (Fig. 13.2). The word delta, however, is used in a more general sense to describe any feature resulting from this type of marginal accumulation, including in lakes, lagoons, ponds and reservoirs. Deltas form where conditions in the receiving basin are not energetic enough to disperse all of the sediment brought down by rivers. The term ‘delta’ comes from Greek for the letter D, and is attributed to Herodotus, the 5th century BC Greek historian who first recognized the similarity of the shape of the subaerial Nile delta to this letter.

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