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Terrace deposit
From Wikipedia, the free encyclopedia
A terrace deposit is geological term for a flat platform of land created alongside of a river or sea, where, at some time in the past, the river has cut itself a deeper channel. The former floodplain of the river is therefore at a higher point and is known as a terrace. Rivers can create a sequence of terraces over millennia as they erode away more material.
Terraces are formed by river rejuvenation, when the river gains in gravitational potential energy. The terraces themselves are often made from fluvial material previously dumped by the river to create the earlier floodplain, These terrace deposits are broadly horizontal layers of gravel, sand and finer sediments that can sometimes contain prehistoric archaeological finds.
Another notable source of stream terracing is the aggradation of legacy sediments behind dams. These sediment deposits can accumulate very rapidly, in under 300 years, and can be observed to be in excess of five meters in height.
Here is a good example of a River Terrace: http://www.geographie.uni-erlangen.de/mrichter/gallery/photos/asia/images/river_terraces_near_kasbeki.jpg
