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Songhua River, northeast China. Swirls and curves, showing paths the river once took, as well as oxbow lakes, are easily seen in this satellite photo.

An oxbow lake is a U-shaped lake water body formed when a wide meander from the mainstem of a river is cut off to create a lake. This landform is called an oxbow lake for the distinctive curved shape that results from this process. In Australia, an oxbow lake is called a billabong.

When a river reaches a low-lying plain in its final course to the sea or a lake, it meanders widely. Deposition occurs on the convex bank (known as a point bar) because of the ‘slack water’, or water at low velocity. In contrast, both lateral erosion and undercutting occur on the concave bank (or cut bank) where the stream’s velocity is the highest. Continuous erosion of a concave bank and deposition on the convex bank of a meandering river cause the formation of a very pronounced meander with two concave banks getting closer. The narrow neck of land between the two neighbouring concave banks is finally cut through, either by lateral erosion of the two concave banks or by the strong currents of a flood. When this happens, a new straighter river channel is created and an abandoned meander loop, called a cut-off, is formed. When deposition finally seals off the cut-off from the river channel, an oxbow lake is formed. This process can occur over a time scale from a few years to several decades and may sometimes become essentially static.

A Horseshoe or oxbow lake near Hughes, Arkansas, USA.
The bulges in the border reflect changes in the course of the river; when the river shifted its course and cut off the former channel, the border did not change.

By itself, the word oxbow can also mean a U-shaped bend in a river or stream, whether or not it is cut off from the mainstream.^[1][2]

Early stages of formation of coastal plain ox-bow lake. Gower Peninsula, southwest Wales

The Reelfoot Lake in west Tennessee is an oxbow lake formed when the Mississippi River changed course following the New Madrid Earthquake of 1811–1812. There are many oxbow lakes alongside the Mississippi River and its tributaries. The largest oxbow lake in North America, Lake Chicot (located near Lake Village, Arkansas), was originally part of the Mississippi River.

The town of Horseshoe Lake, Arkansas is named after the horseshoe shaped oxbow lake at the eastern tip of which the town is located.

Cuckmere Haven in Sussex, England contains a widely meandering river with many oxbow lakes, often referred to in physical geography textbooks.

1. ^ Ask Oxford.
2. ^ Merriam-Webster.

• NASA Remote Sensing Tutorial: Fluvial/Deltaic/Coastal Landforms

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Oxbow lakes