Alluvium (from the
Latin, "alluvius", from "alluere", "to wash against") is soilor sediments deposited by a river or other running water. Alluvium is typically made up of a variety of materials, including fine particles of siltand clayand larger particles of sandand gravel.
Flowing water associated with glaciers may also deposit alluvium, but deposits directly from ice are not alluvium (see
A river is continually picking up and dropping solid particles of rock and soil from its bed throughout its length. Where the river flow is fast, more particles are picked up than dropped. Where the river flow is slow, more particles are dropped than picked up. Areas where more particles are dropped are called alluvial or
flood plains, and the dropped particles are called alluvium.
Even small streams make alluvial deposits, but it is in the
flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found.
The amount of matter carried by a large river is enormous. The names of many rivers derive from the color that the transported matter gives the water. For example, the
Huang Hein China is literally translated "Yellow River", and the Mississippi Riverin the United States is also called Big Muddy. It has been estimated that the Mississippi Riverannually carries 406 million tons of sediment to the sea [cite book | last = Mathur | first = Anuradha | coauthors = Dilip da Cunha | title = Mississippi Floods: Designing a Shifting Landscape | publisher = Yale University Press | date = 2001 | location = New Haven, CT | isbn = 0-300-08430-7] , the Huang He796 million tons, and the Po Riverin Italy 67 million tons [cite book | last = Dill | first = William A. | title = Inland fisheries of Europe | url = http://www.fao.org/docrep/009/t0377e/t0377e00.htm | publisher = UN Food and Agriculture Organization | date = 1990 | location = Rome, Italy | isbn = 92-5-102999-7] .
Alluvium often contains valuable ores such as
goldand platinumand a wide variety of gemstones. Such concentrations of valuable ores is termed a placer deposit.
Throughout history, many shallow lakes have been filled in with alluvium to leave
fertileplains (alluvial soils are often very fertile). The alluvial mud annually deposited by the Nilehas enabled the Egyptians to grow crops since at least the 4th millennium BCwithout artificial fertilization.
Since the construction of the
Aswan Damon The Nilein Egypt, 95% of the alluvium deposits at the mouth of the Nubia-Nasser Lakeare gone, thus depriving the Nile deltaof its fertility. Since 1964, 3.8 billion cubic meters of sediments have deposited in this man-made lake. Proposals have been made to dredge this alluvium and pump it in slurry pipelinesto shore where it can be used to fertilize the desert. [ABULNAGA Baha - EL-SAMMANY Moustafa " Mine Over Water" International water power & dam construction (Int. water power dam constr.) ISSN 0306-400X CODEN IWPCDM International water power and dam construction - 2003, vol. 55, no11, pp. 22-26 ]
*"Dennis Garrett", [http://www.alaskafreegold.com Blue Ribbon Mine, Alaska]
Wikimedia Foundation. 2010.