Erosional and depositional landforms
Meanders
As the river makes its way to the middle courseThe middle section of a river which has sloping land., it gains more water and therefore more energy. lateral erosionThe wearing away of the landscape when a river erodes sideways. starts to widen the river. When the river flows over flatter land they develop large bends called meanderA bend in a river..
- 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 actionErosion caused by the force of river water hitting cracks in the side of the river bank. The air in the cracks becomes compressed and then explodes outwards, breaking off bits of rock. and abrasionWhen rocks carried by the sea water wear away the landscape, eg cliff face/headland.).
- The lateral erosion on the outside bend causes undercutting of the鈥痓ank鈥痶o form a river cliffSteep bank created on the outside of a river bend by the erosive effect of fast-flowing water undercutting the bank..
- Water on the inner bend is slower, causing the water to slow down and deposit the eroded material, creating a gentle slope of sand and shingle.
- The build-up of deposited sediment is known as a slip-off slopeGently sloping bank found on the inside of a river bend because of slow-flowing water, depositing sediment. (or sometimes river beach).
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 meanders move closer together. When there is a very high dischargeThe volume of water in a river passing a point in a given time. Measured in cumecs (cubic metres per second). (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.