The current of the water removes , transports and deposits crushed, predominantly mineral solids in the form of rubble ( gravel , crushed stone ), sand and mud along a river . More material is carried away (eroded) than deposited at fast-flowing parts of the river. Only in places with less flow is more deposited than eroded. Only sand and mud are deposited on particularly sluggishly flowing river sections, from which the alluvial soils are formed. This occurs particularly in estuary deltas and in the so-called alluvial plains away from coasts and lakes.
The amount of solids carried and deposited by large rivers is enormous. The names of many rivers refer e.g. B. on the color of the fine-grained material, which is transported in suspension by the river and gives it its color. The name of the Chinese river Huang He means “Yellow River” and the Missouri River in the USA is nicknamed Big Muddy (literally: big muddy). It is estimated that the Mississippi River in the USA annually transports 406 million tons of loose sediment , the Huang He even about 796 million tons and the Italian Po still about 67 million tons.
Although smaller rivers can also cause such deposits, it is the alluvial soils in large river deltas that have a certain geological importance. These floors are typically made from a variety of different materials. The fine components, also known as silt , consist mainly of sand and clay . But also larger particles such as B. Gravel and rubble are often available in a wide range of grain sizes. In addition, these alluvial soils can contain large amounts of ores , precious metals such as gold and platinum, and precious stones . Such so-called soap deposits can be very productive. Alluvial soils are usually very rich in nutrients due to their mostly high content of organic compounds . For example, the annual deposition of sediments on the banks of the Nile means that grain has been grown in Egypt without artificial fertilization since the 4th millennium BC . In the course of time, many shallow lakes have been inundated with alluvios, creating very fertile areas.
- P. Vageler: The Mkatta plain. Contributions to the knowledge of the East African alluvial soils and their vegetation. Berlin 1910.
- The earth. Journal of the Society for Geography in Berlin. 1963.
- Edwin Blank (Hrsg.): Handbuch der Bodenlehre. J. Springer, 1929.
- Soil Research: Soil science research (Recherches sur Le Sol). International Society of Soil Science, 1928.
- William A. Dill: Inland fisheries of Europe. UN Food and Agriculture Organization, Rome, Italy 1990, ISBN 92-5-102999-7 .
- Schüler Duden (Ed.): The geography . Dudenverlag, Mannheim 1991, ISBN 3-411-04222-2 , pp. 16 .