Processes forming river landscapes - middle course
Meander
- Water twists and turns around stones and other obstructions resulting in areas of slower and faster water movement.
- The river starts to flow from side to side in a winding course but still in a relatively straight channel.
- Water moving faster has more energy to erode. This occurs on the outside of the bend and forms a river cliff.
- The river erodes the outside bends through corrasion, corrosion and hydraulic action.
- Water moves slowly on the inside of the bend and the river deposits some load, forming a river beach/slip-off slope.
- Continuous erosion on the outer bankThe outside bend of a meander. and deposition on the inner bankThe inside bend of a meander. forms a meander in the river.
- The meander will migrate downstream and change shape over time.
Oxbow lake
- The river is meanderingWhen a river winds its way downstream. across the valley.
- The river is eroding laterally (from side to side).
- The river flows faster on the outside bends and erodes them.
- The river flows slowly on the inside bends and deposits material so its course is changing.
- Continual erosion and deposition narrows the neck of the meander.
- Often during a flood the river will cut through the neck.
- The river continues on its straighter path and the meander is abandoned.
- New deposition seals off the ends and the cut-off becomes an oxbow lake that will eventually dry up.