River landforms Flashcards
What are upper course features?
Steep sided v- shaped valleys interlocking spurs rapids waterfalls gorges
What are middle course river features?
Wider, shallower valleys
meanders
oxbow lakes
What are lower course river features?
Wide flat-bottomed valleys
floodplains
deltas
What happens at the upper course?
As the river moves through upper course, it cuts downwards. The gradient here is steep and the river channel is narrow. There’s more vertical erosion in the upper course. Vertical erosion helps create the upper course features.
How are interlocking spurs created?
As the river erodes landscape in upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs.
When do rapids and waterfalls form?
When a river runs over alternating layers of hard and soft rock
What happens in the middle course?
River has more energy and a high volume of water. Gradient is gentle and lateral (sideways) erosion has widened the river channel. River channel has also deepened. A large river channel means less friction, so water flows faster.
How are meanders formed?
As the river erodes laterally (to the right then left) it forms large bends and then horse-shoe like loops called meanders.
What is the cause for the formation of meanders?
Due to the deposition and erosion and meanders gradually migrate downstream.
What does the force of the water do in meanders?
The force of the water erodes and undercuts the river bank on the outside of the bend where water flow has the most energy due to decreased friction
What happens on the inside of the bend?
The river flow is slower, material is deposited as there’s more friction
How do oxbow lakes form?
The horseshoe becomes tight overtime, until the ends become very close together. As the river breaks through, e.g during a flood when the river has a higher discharge and more energy, and the ends join, the loop is cut-off from the main channel. The cut off loop is called an oxbow lake.
How is a new meander formed?
Upstream a large bend becomes a horseshoe and is eventually cut-off to become an oxbow lake. Downstream the river is eroding its outer bank and depositing on its inner bank to create a new meander.
What happens in the lower course?
in the lower course the river has a high volume and a large discharge. The river channel is deep and wide and the landscape around it is flat. As the river reaches the end of its journey, energy levels are low and deposition takes place.
What is a floodplain?
The area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich sediment deposited by floodwaters. A build up of sediment on the banks of a river can create levees, which raise the river bank. (floodplains are good for agriculture)
