Upper, middle and lower course of a river Flashcards
Upper course:
What is an interlocking spur?
In the upper course there is more vertical erosion. The river cuts down into the valley. If there are areas of hard rock which are harder to erode, the river will bend around it. This creates interlocking spurs of land which link together like the teeth of a zip.
Upper course:
How is a v-shaped valley formed?
Rivers begin high up in the mountains so they flow quickly downhill eroding the landscape vertically.
The river cuts a deep notch down into the landscape using hydraulic action, corrasion and corrosion.
As the river erodes downwards the sides of the valley are exposed to freeze-thaw weathering which loosens the rocks (some of which will fall into the river) and steepens the valley sides.
The rocks which have fallen into the river help the process of corrasion and this leads to further erosion.
The river transports the rocks downstream and the channel becomes wider and deeper creating a V-shaped valley between interlocking spurs.
Upper course:
How is a waterfall formed?
The river flows over bands of softer and harder rocks.
Softer rock is more quickly eroded.
The river undercuts the harder rock leaving an overhang.
The river forms a plunge pool below the waterfall.
Overhanging rock is unsupported and falls into the plunge pool.
The waterfall is moved upstream.
This process continues and a gorge is cut back into the hillside.
Middle course:
How is a meander formed?
Water twists and turns around stones and other obstructions resulting in areas of slower and faster water movement.
The river starts to flow from side to side in a winding course but still in a relatively straight channel.
Water moving faster has more energy to erode. This occurs on the outside of the bend and forms a river cliff.
The river erodes the outside bends through corrasion, corrosion and hydraulic action.
Water moves slowly on the inside of the bend and the river deposits some load, forming a river beach/slip-off slope.
Continuous erosion on the outer bank and deposition on the inner bank forms a meander in the river.
The meander will migrate downstream and change shape over time.
Middle course:
How do you form an ox bow lake?
The river is meandering across the valley.
The river is eroding laterally (from side to side).
The river flows faster on the outside bends and erodes them.
The river flows slowly on the inside bends and deposits material so its course is changing.
Continual erosion and deposition narrows the neck of the meander.
Often during a flood the river will cut through the neck.
The river continues on its straighter path and the meander is abandoned.
New deposition seals off the ends and the cut-off becomes an oxbow lake that will eventually dry up.
Lower course:
How is a levee formed?
The river is on its floodplain with a very low gradient.
The river is mainly depositing (silt and sand).
When the river floods a lot of silt is deposited on the river banks and much less on the floodplain.
Frequent flooding continues this build up.
When the river is flowing normally it deposits in the river bed.
This raises the river above the floodplain.
Usually the built-up levées protect the plain from flooding.
