How is a meander formed?

With distance downstream, the river gains more energy and a higher volume of water (as shown in Bradshaw's Model). Because the channel has increased in size, there is less friction. As the river erodes laterally (to the sides), it forms large bends and loops according to where the ground is easier to erode (ie where there is sofer, less resistant rock). A meander forms due to both deposition and erosion on either side of the river channel. On the outside of the bend, there is more energy due to decreased friction, so the force of the water erodes and undercuts the bank on this side. However on the inside of the bend, where the river flow is slower, the material is deposited. This side is called the "slip off slope".