Weathering and Erosion
Weathering breaks down rocks and makes it easier for the processes of erosion and transportation to operate.
In upland areas, the process of 'freeze-thaw' weathering can shatter rocks on valley sides. Rock fragments fall into river channels amd are shaped and moved by processes of erosion and transportation.
There are four main processes of erosion:
- Abrasion/Corrasion: fragments of rock carried by a river wear away the bed and banks of the river. When a river is in flood it can carry tons of material and the effect of abrasion will be greater. It is responsible for the deepening of river valleys in upland areas.
- Attrition: pebbles and rocks collide with each other, reducing their size and making them increasingly smooth.
- Hydraulic Action: the power of moving water being forced against river banks causes them to collapse and be washed away.
- Corrosion/solution: chemical reaction occurs when slightly acid water dissolves calcium, breaking down rock such as limestone.
The ability for a river to erode depends on the amount of energy it has. This is variable because it depends on the volume of the water in the river. After heavy rainfall, the volume of water will increase and it will have more energy. This gives it the power to move significant amounts of materials, including large rocks and boulders.
After a prolonged period of dry weather, the volume of the water in the river…