New Geography in Action Junior Cycle Geography Deltas
Deltas are landforms of deposition found in the old stage of a river. A delta is a triangular or fan- shaped area of land at the mouth of the river where it enters a lake or the sea.
Formation: • The river slows down when it enters a lake or the sea and loses energy, causing it to deposit its load.
• Deltas form where river mouths become choked with sediment, causing the main river channel to split into many smaller channels or distributaries on their way to the sea. Deltas form only under certain conditions:
• The river must be transporting a large amount of sediment.
• The sea must have a small tidal range and weak currents.
• The sea must be shallow at the river mouth.
Examples of deltas: the Mississippi delta in the USA, the Ganges and Brahmaputra delta in India and Bangladesh, and the Nile delta in Africa.
ACT VITY
Can you apply the D-E-P-E-D formula to explain one landform of river deposition to your classmates? Use the outline on page 41 of your Activity Book to help you.
: Figure 9.21 The structure of a delta Delta
Distributary channels
(i) Name the three stages of a river. (ii) Why does deposition become the main process in the old stage of a river?
(iii) Name two landforms found at each stage of the river and state whether they are landforms of erosion or deposition.
(iv) Explain how each of the processes of erosion can be involved in the formation of waterfalls.
/ I can identify all landforms of erosion and deposition and I understand their formation in the youthful, mature and old stages of a river.
/ I can explain in detail the formation of one landform of erosion. / I can explain in detail the formation of one landform of deposition.
