Fluvial (river) processes Flashcards
erosion
the process by which a river wears away the land
transportation
the process by which a river carries its load
deposition
the process by which a river drops its load
what are the types of erosion?
-abrasion
-hydraulic action
-corrosion
-attrition
abrasion
erosion of banks and beds by load transported by a fast flowing current
hydraulic action
the sheer force and power of moving water on the sides of the river bed and in the cracks of the rock
corrosion
chemical action that dissolves the bed and banks
attrition
erosion of the bedload by contact with other loads, the bed and the banks, attrition rounds and smooths the bedload
what are the different types of transportation?
-traction
-saltation
-suspension
-solution
traction
heavy rocks and boulders are rolled along the river bed when the current is strongest
when does traction happen the most?
happens most in times of flood
saltation
small pebbles are bounced along the river bed when river flow is less than that needed for traction to take place
suspension
very small particles of sand or clay that are suspended in the water, these particles will settle if kept in a jar of water overnight and the water will look clear
solution
takes place when material is dissolved in water, it is invisible and does not colour the water
when does solution occur?
often in limestone landscapes where the water is very acidic
when does deposition occur?
when there is a reduction in river velocity which results in its load being deposited, starting with the largest sediment as this requires a lot of energy to remain in suspension
how does deposition occur?
- there is a sudden reduction in gradient
- the river enters a lake or a sea
- river flow has reduced following a period of low rainfall
- where there is shallow water
5.there is a sudden increase in the volume of sediment available - river overflows its bank so velocity outside the channel is reduced
how do fluvial processes cause vertical erosion?
hydraulic action deepens the river as there’s little energy left after overcoming friction which deepens the channel by eroding downwards
how do fluvial processes cause lateral erosion?
when the river goes into lower course it becomes less steep and it starts to meander, when the water goes round a bend the water is forced onto the outside of the bend which causes erosion sideways
what does the Hjulstrom curve show?
it’s very difficult for rivers to get smaller rocks moving but once they’ve been picked up they are very easy to transport
