What Are They? Edit
They are crescent-shaped lakes or wetlands which are the remainders of cut-off meanders on a floodplain. After the evaporation of all the water, they are referred as 'meander scars'.
How are they formed? Edit
Ox-bow lakes are formed in the lower course of a river, when the river forms large meanders. The flow of water is faster on the outside bend where erosion is most dominant. The river-cliff is subject to Hydraulic Action and Abrasion. On the inside bend, deposition is dominant. This leads to an accumulation of sand, rocks and other materials carried by the river as a point-bar or slip-off slope.
Eventually after time, the neck of the meander becomes narrower due to erosion on the outside. This stage is known as a 'gooseneck' meander.
Eventually a surge of water (often during flooding) breaks through this neck, straightening the river and also forming an oxbow which it is still connected to. Slowly, layers of alluvium build up on the neck of the oxbow. This eventually cuts it off from the river. Forming an oxbow lake. Starved from a supply of water, the lake eventually dries up and leaves a meander scar.
Although cut-off may occur rapidly, the entire cycle of meandering and oxbow lake formation is likely to take several hundred years or more. Oxbow lakes are common on the lower course of the Mississippi - a large-scale example is the 10km long Moon Lake.