The river valley Flashcards
What is hydraulic action?
The sheer force of the water hitting the bed and banks causes erosion.
When is hydraulic action most effective?
When the water is moving fast and when there is a lot of water
What is abrasion?
It occurs when the load the river is carrying repeatedly hits the river bed and the banks, causing some of the material to break off
What is attrition?
When the stones and boulders carried by the river knock against each other and over time are weakened, causing bits to fall off and reduce in size
What is solution erosion?
Solution occurs when the river flows on certain types of rock, such as chalk and limestone. These are soluble in rainwater and become part of the water as they are dissolved by it
Which ways can a river erode?
Downwards (vertical) and sideways (lateral)
As a river goes further down its course what type of erosion takes over?
As a river gets further down its course, vertical erosion becomes less important and lateral erosion takes over
What are the 4 ways a river transports its load?
Traction, saltation, suspension and solution
What is traction?
Is the method used for moving the largest material. This is too heavy to lose contact with the bed, so material such as boulders are rolled along
What is saltation?
Moves the small stones and grains of sand by bouncing them along the bed. This lighter load leaves the river bed in a hopping motion
What are the four ways a river can erode?
Hydraulic action, abrasion, attrition and solution
What is the river channel?
The part of the river valley occupied by the water itself
What is a rivers load?
Material of any size carried by the river
What is suspension?
Is a means of carrying very fine material within the water, so that it floats in the river and is moved as it flows
What is solution?
The dissolved load and only occurs with certain rock types that are soluble in rainwater. This is true of chalk and limestone and the load is not visible
What is deposition?
Where the river dumps or leaves behind material that it has been carrying
Why does a river deposit its largest material first?
It is the heaviest to carry
Why will a river deposit a smaller load much further downstream
It is smaller so less heavy and can be carried further downstream
Why may a river slow down and deposit some of its load?
The speed of the water slows
The volume of water in the river falls
The amount of eroded material in the water increases
The river reaches its mouth
When specifically may a river deposit its load by the speed of the water or volume of water change?
When the gradient changes at the foot of a mountain or when a river enters a lake or the sea
What is the long profile of a river?
A line representing the course of the river from its source (high up) to its mouth where it ends usually in a lake or the sea, and the changes in height along its course f
Where will a river on its long profile have the most potential energy and why?
Near the source due to the steep drop
What should a typical long profile look like?
A concave shape, the steep reduction in height near the source gives way to a more gradual reduction further downstream
Why is a perfect long profile rare?
Land is uplifted, sea levels change and bands of hard and soft rock cross the path of the river
What is the cross profile of a river?
a line that represents what it would like to walk from one side of the valley, across the channel and up the other side
Generally what does the cross profile show?
The valley becomes wider and flatter with lower valley sides
What are some features of the upper course?
Vertical erosion Shallow, narrow channel Hydraulic action, abrasion, and attrition Some traction and saltation at high flow Deposition of large material Large load
What are the features of the middle course
Some vertical erosion, lateral erosion is more important
Hydraulic action less important
Suspension main, transportation by saltation and traction is still present
Deposition more obvious
Load size reduced
Wider, deeper channel
What is the lower course of a river like?
Less erosion, only little lateral Widest, deepest channel All erosion much less important Suspension dominant Deposition of fine materials Large amount of load size now very small
What forms in areas near the source (upper course) where vertical erosion is dominant?
Waterfalls and gorges
What landforms are made downstream (middle course) where lateral erosion is more dominant
Meanders and oxbow lakes
What landforms are made nearer the mouth (lower course) where deposition is most significant?
Flood plains and levees
Which landforms occur as a result of erosion?
Waterfalls and gorges
Which landforms occur due to deposition?
Levees, flood plains
Which landforms occur as a result of both erosion and deposition?
Meanders and of bow lakes
What is a waterfall?
The sudden and often vertical drop of a river Lang its course
What is a gorge?
A narrow, steep sided valley
