geography (rivers) Flashcards
what affects speed of flow?
river processes
- roughness of channel
- gradient of channel
- wetted perimeter
what affects volume of flow?
- climate
- presence of vegetation
- size of channel
- permeability of rocks
what are the erosional processes?
- corrasion
- attrition
- solution
- hydraulic action
corrasion - grinding action
attrition - softening of edges over time
solution - carbonic acids reacting with limestone
hydraulic action - repeated pounding on cracks widening them
what are the transportational processes?
- Traction
- Saltation
- Suspension
- Solution
traction - rolling of large boulders along surface
saltation - bouncing of small rocks on surface
suspension - not touching surface, fine particles
solution - dissolved substances carried by water
what affects deposition?
- sudden increase in load
- flow along shallow side of river
- entering larger water body
- periods of low precipitation
- presence of vegetation to obstruct
formation of waterfall
erosive landform
- river flows along rocks of alternating resistance
- one eroded more than the other, causes a change in gradient
- over time, river plunges from a great height with tremendous force to form waterfall
- repeated pounding on riverbed causes depression known as plunge pool, has rocks swirling in it
formation of valley
- is a low area between hills and mountains
- in upper course river has enough energy to erode vertically downwards, so valleys are steep and v shaped
- in lower course river erodes laterally, so valley is U shaped and wide
formation of levees
depositional landform
- during a period of high precipitation, the volume of river will suddenly increase
- the channel cannot hold this increased volume so it overflows its banks and causes floods
- as floodwater spreads it slows down and deposits its load
- heavier load deposited first and finer load deposited last
- over time the load is stacked up and a natural levee is formed
formation of deltas
- river will begin to deposit load when it reaches the sea
- over time the accumulation of sediments will form an extensive platform jutting out into the sea
- plants will grow on the platform to stabilise it, hence a delta is formed
factors affecting formation of delta
- many tributaries to ensure high volume of load
- tidal wave must not be too strong to remove deposited sediments
- no large body of water in the river to trap sediments
- active erosion in river to ensure constant supply of load
formation of oxbow lake
erosional and depositional landform
- when a meander becomes very distinct, the neck of land seperating two meanders will slowly reduce
- when it gets cut off, a straight channel with a loop in the side will form
- over time, deposition occurs at the mouths of the loop, and eventuallly it will be cut off from the meander
- the resultant landform is oxbow lake which will then be dried up eventually due to lack of source
what are the uses of river
Transport
+opportunity for trade
-oil spills pollution etc
industry
+can increase production and gdp
-can cause pollution yet again
tourist attractions
+can increase gdp
-pollution
