Erosional and depositional landforms

Meanders

As the river makes its way to the middle course, it gains more water and therefore more energy. Lateral erosion starts to widen the river. When the river flows over flatter land it can develop large bends called meanders.

  • As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed and therefore increased erosion (through hydraulic action and abrasion).
  • A steep bank called a river cliff is created on the outside of the meander.
  • The lateral erosion on the outside bend causes undercutting of the river cliff leaving an overhanging bank.
  • Water on the inner bend is slower, causing the water to deposit eroded material, creating a gentle slope of sand and shingle.
  • The build-up of deposited sediment is known as a slip-off slope (or sometimes river beach).
The fast current on the outside bank causes lateral erosion, creating a river cliff. The slow current on the inside bank causes deposition, creaitng a slip-off slope.

Oxbow lakes

Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time. Erosion narrows the neck of the land within the meander and as the process continues, the meander necks move closer together. When there is a very high discharge (usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.

Erosion makes the neck narrow. During floods, the river takes the shortest course through the neck. The river has a new straighter course and the abandoned meander is called an oxbow lake.