Everything about Alluvial Deposit totally explained
Alluvium (from the
Latin,
alluvius, from
alluere, "to wash against") is
soil or
sediments deposited by a river or other running water. Alluvium is typically made up of a variety of materials, including fine particles of
silt and
clay and larger particles of
sand and
gravel.
Flowing water associated with glaciers may also deposit alluvium, but deposits directly from ice are not alluvium (see
glacial till).
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's in the
flood plains and
deltas of large rivers that large, geologically-significant alluvial deposits are found.
The amount of solid 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 He in China is literally translated "Yellow River", and the
Missouri River in the United States is also called Big Muddy. It has been estimated that the
Mississippi River annually carries 406 million tons of sediment to the sea, the
Huang He 796 million tons, and the
Po River in Italy 67 million tons.
Alluvium often contains valuable ores such as
gold and
platinum and 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
fertile plains (alluvial soils are often very fertile). The alluvial mud annually deposited by the
Nile has enabled the
Egyptians to grow crops since at least the
4th millennium BC without artificial fertilization.
Since the construction of the
Aswan Dam on
The Nile in
Egypt, 95% of the alluvium deposits at the mouth of the
Nubia-Nasser Lake are gone, thus depriving the
Nile delta of 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 pipelines to shore where it can be used to fertilize the desert.
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