Alluvium is the result of water flow

What is alluvium? The definition of this term can be given in many ways. It all depends on who is interested in this subject. For a schoolboy, for a student, for a housewife, for a simple layman, the definitions may sound different.

Probably, every man has been to the river for once. And if this happened in the spring, during the flood, he would have noticed a huge amount of various material (stones, fragments of rocks, blocks, sand, silt, branches of trees and shrubs, well, if not different anthropogenic debris), dragged downstream . In principle, all this is alluvium.

So, alluvium is everything that a river carries with it? No, not exactly. Then, maybe, the alluvium is part of the riverbed that the river makes to itself in the parent rock? Not at all.

Scientific definition of the term

Well, let's give him a scientific definition after all. Alluvium is a sediment deposited by water streams, consisting of rounded and sorted clastic material, as well as organic matter. The very word comes from the Latin alluvio, which means "nanos", "namiv".

Alluvium of plains and mountain rivers

There are two main types of alluvium, which depend primarily on tectonics and the terrain where the river flows. It is an alluvium of mountainous and lowland rivers.

Alluvium of mountain rivers

Rivers in the mountains are usually characterized by a high flow velocity, their deposits consist mainly of boulders and pebbles. The other smaller and soft rocks do not have time to linger on the river and are carried downstream.

Nanosam of mountain rivers are characterized by the following features:

• They consist of coarse detrital material, in which the pebble is predominant;
• A diverse mineral composition of debris;
• Weak sorting of the material;
• There is no clear stratification.

Alluvium of lowland rivers.

Plain rivers have a lower flow velocity and, accordingly, they are not capable of carrying large debris over long distances.

Therefore, the deposits of flat rivers are characterized by other features:

• Consist of a fine-grained material, in which sand and sandy loam predominate;
• Fairly homogeneous mineral composition;
• Good sorting of material;
• The presence of coarse oblique lamination, which is transformed into a shallow oblique layering.

Zoning of river alluvium and its characteristics

Zoning is characteristic of almost any natural phenomenon or object. Although for alluvial soils it is less pronounced than for others, and their main constituent is just alluvium. This, however, does not exclude the effect of zonality on alluvium, primarily on its mineral composition and acidity.

True, the larger the river and its floodplain, the weaker is the zoning of alluvial deposits.

On the average, in the northern humid regions, alluvial soils usually have an acid reaction, they are characterized by the absence of carbonates and non-salinity. With the advance to the south, in the more arid regions, they acquire a neutral, and then an alkaline reaction, characterized by a saturated carbonate content.

Delta, floodplain, old and channeled alluvium

Alluvial deposits in the flat rivers differ in complexity and variety. Therefore, according to the nature of precipitation and the places of their accumulation, it is common to divide alluvial deposits into channel, delta, floodplain and old-earth sediments.

Delta alluvium is formed in deltas of rivers and is characterized by sandy-clayey composition.

Channel alluvium is formed in riverbeds and consists mainly of sand and coarser debris such as boulders, gravel and pebbles. They formed sandbanks, braids and islands on the river.

Flooded alluvium is formed during the flood period and consists of a variety of loam, clay and fine-grained sands enriched with organic.

The old alluvium is deposited at the bottom of the vintage and consists of mud with a lot of organic matter.

Alluvial deposits are widespread all over the world. Long ago it was on their development that all the major ancient world civilizations, such as Ancient Egypt in the Nile Valley or Ancient Mesopotamia in the valleys of the Tigris and Euphrates rivers began to emerge.

In the modern world, the most productive agricultural lands are located in the territories with floodplain alluvium. It also often contains placers of minerals and even precious minerals.