Incised or Entrenched Meanders

The key to understanding incised meanders lies in the contrast between where meanders usually form and where these particular ones are found. Normally, a meandering river is a sign of maturity and gentleness — it winds lazily across a flat floodplain. But an incised meander is a deep, sweeping curve carved directly into solid rock, a dramatic reminder that a river's history can be far more complex than its present appearance.

To see why this happens, start with the river's gradient. A stream flowing rapidly over a steep slope directs most of its erosive energy downward, scouring the bottom of its channel. Lateral erosion — the sideways cutting that widens a valley — is comparatively weak on such steep gradients. This is why steep mountain streams tend to run straight and narrow, cutting deep gorges rather than wandering.

The situation reverses on gentle slopes. Here, the stream's energy is spent less on downward cutting and more on sideways erosion. This active lateral erosion undercuts the banks, allowing the river to develop a sinuous, meandering course. It is common to find such meandering courses over floodplains and delta plains, where the gradient is very gentle and the river has the freedom to swing back and forth across its own deposits. …