Middle Course Processes and Features Flashcards
What are meanders?
Bends in the course of a river.
What is the thalweg?
The fastest flow.
Where is the fastest and slowest flow and what processes occur with each one?
Fastest flow, outside bend, erosion
Slowest flow, inside bend, deposition.
What does sinuous mean?
Bendy
How are meanders formed?
Water flows slowly over shallow areas (riffles) in the riverbed and faster through the deeper sections (pools). This sets in motion a helicoidal (spiralling) flow that corkscrews across from one bank to another. This starts the erosion and deposition which shape a meander.
What is riffle?
Deposited rock that might stick out. Riffles cause friction with water flow making the flow slower.
What is a pool?
An area of fast flowing water.
What does the helicoidal flow do?
Removes material from the outside bend.
How is an oxbow lake formed?
1) Narrow neck of the meander is eroded.
2) This creates a short cuts, causing the bend of the meander to stop being used as the main flow.
3) A new straight river course is formed, making a redundant loop.
4) Deposition occurs helping to infill and detach the loop. Marsh plants colonise, drying out the area. The loop becomes and oxbow lake.
How is an oxbow lake formed (In depth)?
1) Water in a meander is pushed to the outside bend.
2) Greater velocity means that the river has more energy to erode.
3) Processes such as abrasion will cause lateral erosion
4) continual erosion on the outside bend narrows the meander neck
5) The river floods and takes the shortest route, cutting through the neck.
6) The thalweg is now in the centre of the channel.
7) Deposition occurs along the banks of the river.
8) the meander becomes cut off to leave an ox-bow lake.
9) the lake will slowly dry up unless rainfall is very high.
What are the characteristics of an ox-bow lake?
- Steep drop to the lake down former cliff
- deepest water at the outside edge
- Fairly stagnant water
- Marsh plants colonise the edges
- gentle slip off slope into the lake on inside bend.
