Alluvial soil consists of clay, silt, sand, gravel, metals and other earthly material and is typically found near a water source. Build-up of alluvial soil in moving water can change the water's flow.
Alluvium refers to loose soil or sediments that have been eroded and reshaped by moving water and moved to another area. Alluvial soil has been found to contain iron ore, gold, platinum, gemstones and tin ore. Typically, alluvium sediment is younger than the rock on which it lands and can therefore cause confusion as to the age of the rock underneath and in the surrounding area. Large quantities of alluvial soil can form floodplains, deltas and fans. Examples of large alluvial deltas can be found in the Mississippi, Nile, Ganges, Brahmaputra and Huang rivers. Alluvial soil fans are deposits that form a triangular shape as a result of runoff from moving water, such as a fast-moving stream, canyon or waterfall. The running water carries the alluvial soil to a flat plan, where it spreads out and changes the flow of water around it. The narrow point of the alluvial fan is called the apex, and the wide triangle part is called the apron. Because alluvial soil contains many nutrients and comes from a water source, it is excellent soil for planting.