Rivers Flashcards
What is the long profile of a river?
How a river changes in gradient across its whole course
What is a cross section of a river?
How the cross section of a river channel and valley vary at points along a river
What is the cross section of a river in its upper course?
Steep valley sides.
Narrow and shallow channel.
What is the cross section of a river in its middle course?
Wider valley and some erosion on sides of valley.
Wider river channel with floodplain.
What is the cross section of a river in its lower course?
Wider, almost flat river valley with gentle slopes.
Wider and deepest channel with a large floodplain.
What type of erosion happens in the upper course of the river and why?
Vertical because the discharge is smaller but faster
What type of erosion happens in the middle course of the river and why?
Lateral becasue the material carries by the river can erode the banks
What is hydraulic action?
When the force of the river compresses air trapped in cracks in the banks and the increased pressure weakens and gradually wears away at the banks.
What is abrasion?
When rocks carried by the river rub and scrape along the river bed and banks, wearing them down.
What is solution?
When water is slightly acidic, it dissolves certain types of rocks on the river bed and banks and carries them as the river water flows
What is attrition?
As rocks carried by the river collide within each other and break into smaller pieces
What is traction?
When large particles are rolled along the river bed by the force of the water at times of high discharge
What is saltation?
When small rocks and sand particles are bounced along the river bed by the low of the water
What is suspension?
When fine clay and sand particles are carried along within the water even at low discharges
How are waterfalls formed?
1) water runs over alternating bands of hard rock on the top and soft rock on the bottom
2) erosion will start to break down the rocks
3) hydraulic action wears away the soft rock as water runs over it
4) overtime the soft rock starts to undercut the hard rock
5) the hard rock is then left unsupported - so overtime the weight of it collapses into the river bed
6) then the fallen rocks will erode the river bed to create a plunge pool
7) the erosional processes will repeat - the waterfall will retreat
8) creating a steep sided gorge
How are meanders formed?
1) As water flows around bends, faster water on the outside of the bend erodes the riverbank, while slower water on the inside deposits sediment.
2) Over time, this process creates pronounced bends in the river, known as a meander.
How are oxbow lakes formed?
1) on the inside of the bend, the flow is slower and so sediment is deposited
2) the neck of the river then grows narrower
3) when the neck of the river breaks through the river will take the shortest route - which is the straight course
4) the loop becomes sealed off altogether as a result of deposition which is known as an oxbow lake
