delta

  a depositional feature found at river mouths under certain conditions. Where the river enters the body of water (sea or lake) there is energy loss and load is deposited. If the rate of deposition exceeds the rate of removal in any current within the body of water then the material will build up. As the upper surface approaches sea-level the river may be forced to split into distributary channels which remain free of further deposition. Plants may colonize the top of the deposit and help it to build up above the sea level to form new land. Three types are identified:

  arcuate - a fan-shape with the 'point' at the river mouth.

  cuspate - a triangular shape with the 'point' facing the body of water and base at the river mouth.

  bird's foot - as it suggests, with the 'toes' pointing out to the body of water.

  It is now thought that the different shapes are formed according to the salinity of the body of water. High salinity means slow mixing and so the sediments flows further out across the body of water creating a cusp. Low salinity means quick mixing and deposition and so more arcuate shapes.