Delta

Delta is the alluvial deposit formed at the mouth of a river from the deposition of the particles which it has held in suspension or rolled forward upon its bed. The term was originally applied to the tract of land thus formed (mainly within historical times) by the Nile, which, being inclosed by two main branches and the sea, has the form of the Greek letter Δ, delta. The formation of deltas depends more upon the absence of opposing currents at the mouth of the river than upon the quantity of sediment held in suspension when it reaches the sea. Deltas are consequently of almost invariable occurrence in inland lakes, in the quiet estuaries of the nearly tideless Mediterranean, and in the sheltered bays and gulfs of other seas. When, on the other hand, there are strong ebb-tides, or powerful oceanic currents, the detritus is carried off into the sea.