Pawtuxet's Oxbow Lake
Animation - from a British school portal
Definition - from Merriam-Webster
A crescent-shaped often ephemeral lake formed in the abandoned channel of a meander by the silting up of its ends after the stream has cut through the land within the meander at a narrow point.
Formation - from Wikipedia, the free encyclopedia
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 because of the ‘slack water’, or water at low velocity.
In contrast, both lateral erosion and undercutting occur on the concave 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. Some rivers shift in this way on a time scale from a few years to several decades whereas others are essentially static.