Topic 4 - River Processes And Pressures (set A)✔️ Flashcards
Features of a rivers upper course? what type of valley and channel shape is expected?
Has a steep gradient with steep sided V-shaped valleys and narrow, shallow channels
Features of a rivers lower course? what type of valley and channel shape is expected?
Has a gentle gradient with very flat, wide valleys and a deep channel
Features of a rivers middle course? what type of valley and channel shape is expected?
Has a medium gradient with gentle sloping valley sides and a wider deeper channel
What is a rivers course?
The path of the river as it flows downhill - from the source (start) to the mouth (end)
Effect of vertical erosion? Where is it dominant?
Deepens the river valley (and channel) making it v-shaped - dominant in the upper course of the river
Explain how is vertical erosion caused?
High turbulence causes the rough, angular particles to be scraped along the river bed, causing intense downward erosion
Features of lateral erosion?which courses is it most dominant?
Widens the river valley (and channel) during the formation of meanders it is dominant in the middle and lower courses
3 features of the river Edens upper course?
- source is in an area of hard, resistant rock
- valley is steep sided, and the channel has a steep gradient due to vertical erosion
- river channel is narrow and shallow - velocity and discharge is low due to friction from rough channel bed
4 features of the river Edens lower course?
- valley is very wide and flat
- high velocity due to little friction from the smooth channel sides
- large discharge - joined by other rivers
- river channel is very wide and deep (more then 50m wide)
3 features of the river Edens middle course?
- middle parts made from softer, easily eroded rocks like sandstone - results in lateral erosion so river becomes wider
- valley sides become gentler slopes and the gradient of the channel is less steep
- river channel becomes wider and deeper and discharge increases as more streams join main river
Explain in depth each stage of how the mechanical weathering ‘ freeze thaw’ shapes valleys?
1) happens when tempertaures alternate above and below 0 degrees
2) water gets into rocks that have cracks - when the water freezes it expands which puts pressure on the rock - when the water thaws it contracts which releases the pressure on the rock
3) repeated freezing and thawing widens the cracks and causes the rocks to break up
How does hydraulic action cause erosion?
The force of water breaks rock particles away from the river channel
How does abrasion cause erosion?how common is this type of erosion?
Eroded rocks picked up by the river scrape and rub against the channel, wearing it away - most erosion is caused by abrasion
Explain how solution causes erosion of sediment?
River water dissolves some types of rock eg chalk
Name the four processes of transportation?
- traction
- saltation
- solution
- suspension
Explain how traction transports sediment along a river?
Large particles like boulders are pushed along the river bed by the force of the water
Explain how saltation transports sediment along a river?
Pebble-sized particles are bounced along the river bed by the force of the water
Explain how suspension transports sediment along a river?
Small particles like silt and clay are carried along by the water
Explain how solution transports sediment along a river?
Soluble materials dissolve in the water and are carried along
Define deposition?what causes it?
Deposition - when a river drops the eroded material its transporting and happens when the river slows down
Give three examples of why a river might slow down?
- the volume of water in the river falls
- amount of eroded material in the water increases
- river reaches its mouth
Explain in depth how a waterfall is formed? Refer to erosion?
1) river flows over an area of hard rock followed by an area of softer rock
2) softer rock is eroded (by hydraulic action and abrasion) more then the hard rock creating a step
3) water continues to go over the step eroding the softer rock more and more
4) steep drop is eventually created called a water fall
Explain in depth how a gorge is created from a waterfall?
1) hard rock is eventually undercut by erosion - it becomes unsupported and collapses
2) collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock (by abrasion) creasing a deep plunge pool
3) over time, more undercutting and collapsing will cause the waterfall to retreat - leaving behind a steep sided gorge
What are interlocking spurs?
In the upper course of a river most erosion is verical which creates steep, v-shaped valleys - the rivers are not powerfull enough to erode laterally (sideways) so they wind around the hillsides that stick out in their path - hillsides that interlock with each other (as river winds around them) are interlocking spurs
What are meanders?
Large bends developed by rivers in their middle and lower courses in areas where there are both shallow and deep sections in the channel
Explain steps 1 and 2 on how a meander forms?
1) current is faster on the outside of the bend because the river channel is deeper (so there’s less friction to slow the water down)
2) so more erosion (abrasion and hydraulic action) takes place on the outside of the bend - which froms river cliffs
Explain steps 3 and 4 on how a meander forms?
3) current is slower on the inside of the bend because the river channel is shallower (so there is more friction to slow the water down)
4) so eorded material is deposited on the inside of the bend - forming slip-off slopes
Explain in depth how a meander can turn into an ox-bow lake?
1) erosion causes outside bends to get closer - until only a small bit of land is left called the neck
2) river breaks through this land during a flood and the river starts to flow along the shortest course
3) deposition of sediment eventually cuts of the meander - forming an ox-bow lake
