Delta Formation PDF

Explain with the aid of a labelled diagram the formation of ONE landform of deposition that you have studied. Landform: Delta A delta is a feature of fluvial deposition that I have studi...

Explain with the aid of a labelled diagram the formation of ONE landform of deposition that you have studied. Landform: Delta A delta is a feature of fluvial deposition that I have studied. A delta is a flat area of land made of alluvium, formed when a river enters a sea or lake. Deltas are found in the old stage of rivers. An Irish example of a delta may be found at the estuary of the River Shannon., while an international example maybe found at the mouth of the River Nile in Egypt. In order for a delta to form the amount of sediment deposited by the river must be greater than the amount of sediment removed by the tides and currents. Therefore, deltas usually form at sheltered river mouths where sea currents and tidal action is weak, like in the Mediterranean Sea. When a river enters the sea or a lake, its velocity decreases as the river is a small body of water meeting a larger body of water (the sea). The river loses its energy and, as a result, the river begins to deposit its load. The deposition is sorted and laid down in three distinctive layers: 1. Fine particles are carried out to sea and are deposited horizontally in advance of the main delta. These are the bottom-set beds. 2. Coarser materials form inclined layers over the bottom-set beds and gradually build out, each one in front of and above the precious ones, causing the delta to advance seawards. These are the fore-set beds. 3. This layer is deposited nearest to the land and is the heaviest layer, fine particles of clays, silts, and muds are laid down, continuous with the river’s flood plain. These are the top-set beds. This material builds up in layers called beds to form islands, which grow and eventually cause the estuary to split up into many smaller streams, called distributaries. Marine deltas form at the mouths of rivers entering the sea, example the Roughty River in Kenmare Bay, Co. Kerry. There are three types of marine delta: Arcuate delta: This is a triangular delta, formed form coarse material. It develops where sea currents are quite strong and the edges of the delta can’t be kept straight, e.g. the Nile Delta. Bird’s foot delta: this consists of fine material and a small number of distributaries that extend out like a claw of a bird’s foot, e.g. the Mississippi Delta. Estuarine delta: This is a delta which is yet to extend beyond the coastline. The sediments have been deposited in the shallow water along the sides of the estuary, e.g. the Shannon Estuary. Should this process occur in a lake, it is called a lacustrine delta (e.g. Glendalough, Co. Wicklow).