How is a oxbow lake made?

Answer 1

As a river meander downstream, erosion occurs on the outside exits of each meander and deposition on the inside exit. (Erosion occurs on the outside because this is where the water is flowing fastest and hence has more energy to erode.)

An oxbow lake is basically formed when the meander behind erodes faster than the one in front. This then causes the river to break through and creates a straighter segment of channel. The water diverts away from the previous meander and chooses the straighter alternative. The water in the meander has low energy so deposits its load which over time will cause the previous meander to be completely cut off from the main river and will cause an oxbow lake.