Meander migration, oxbow lake formation, and neck cutoff events
Meandering rivers migrate laterally as the outer bank erodes (cut bank) and the inner bank accretes (point bar), driven by helical secondary flow in bends. As sinuosity increases, meander loops tighten until the neck between two bends becomes narrow enough that a flood cuts across, isolating the old loop as an oxbow lake. The cutoff straightens the channel locally, but sinuosity rebuilds — this cyclical process is a fundamental rhythm of alluvial valley evolution.