Question

Why are alluvial soils also called riverine soils?

Answer 1

Hint: Alluvial soils are those that have been deposited by surface water. They can be found along rivers, in floodplains and deltas (such as the Mississippi Delta), on stream terraces, and in areas known as alluvial fans. This category is caused by larger floods, which cause the soil to spread out in the shape of a triangle fan.

Complete answer:
Alluvial soil is also known as riverine soil because it is found in river basins and is formed when the velocity of streams and rivers slows. Alluvial soil is formed by the deposition of sediments carried by rivers starting from the mountains (its origin). When the river overflows, this soil is deposited on the riverbanks.

These soils differ from many other soils in that they are formed through a long process of rock transformation that can take millennia.

Alluvial soils serve many functions, the most important of which is to act as the earth's kidneys. Alluvial soils filter sediments and nutrients from flowing water. They can also remove other pollutants from rivers and improve water quality for downstream users.

Because floods deposit new sediment at the surface on a regular basis, alluvial soils can have a distinct layered appearance. The dark and light colours alternate, as do the various sizes of round gravel particles. This distinct layering process is known as stratification, and it can be seen in many floodplains.

Alluvial soils are formed by flooding. The new sediment is derived from the stream watershed. And it is susceptible to changes in land use. Examples include deforestation, agricultural ploughing, and disturbance during construction activities. These human activities can cause upland erosion, and the resulting sediment flows downriver and is deposited.

Moving eroded soil and nutrients from one location to another can be beneficial at times. Many ancient civilizations, such as Mesopotamia and ancient Egypt, thrived on river banks. Their agricultural societies would not have thrived if not for the fertile alluvial soils deposited on the riverbanks.

Flood deposition can also bring contamination from upland pollution in some cases. Floodplains containing potentially harmful chlorinated compounds and trace metals are more likely in urban and industrial watersheds. Pollution can be visible at times, with dead plant life and garbage on the soil's surface. However, the contamination is not visible in other areas. Soil testing is required.

Note: Many different soil colours, chemical properties, and human artefacts have been discovered buried in floodplains around the world. These enable scientists to retrace the history of human occupation and land use. Alluvial soils in modern urban areas contain discarded garbage that has been carried in with flood waters and buried. Plastics are commonly found in the most recent surface deposits. Older manufactured materials, such as glass, brick, and stone, can be found in deeper deposits. As a result, alluvial soils are critical areas for archaeologists and soil scientists to date human occupation.