Meanders are formed because continuous erosion at the undercut slope (the side slope directly impacted by the channel flow) widens the river bends and steepens the side slope while the slip-off slope becomes flatter due to deposition. However, since the slip-off slope is at the neck of the meander, it becomes narrower and narrower as a result of erosion, and eventually the river cuts through and changes its course. The old meander turns into an oxbow lake, while the hill or terrace where the slip-off slope is located becomes a meander core. This is a typical combination of meander geometry.