rivers Flashcards
where are interlocking spurs found?
upper course
what are interlocking spurs?
“fingers” of land that jut out into the river valley
formation of an interlocking spur?
the river cuts into the valley if there are areas of hard rock which are harder to erode, the river will bend around it
where are waterfalls found?
long profile of a valley
formation of a waterfall?
when the river cannot erode the hard rock, a “step” is formed in the long profile of the river
fast- flowing water plummets over a vertical cliff into a plunge pool
where are gorges found?
at the bottom of the waterfall
how is a gorge formed?
erosion (hydraulic action) and abrasion undercuts the hard rock- forming the waterfall- creating an overhang
the overhang collapses into the plunge pool- waterfall retreats upstream
the undercutting and collapse continues and a gorge is formed downstream
where is a meander found?
middle and lower course
how is a meander formed?
a meander is a fast flowing river that is created due to deposition and erosion.
on the outside bend, there is the fastest velocity (thaldwig) and deeper channels and less friction. there are high levels of lateral erosion which undercuts the river bank and forms a steep- sided river cliff.
the inside bend has more friction and less velocity.
over time, due to erosion and deposition, meanders change shape and move across the floodplain and migrate downstream
where are oxbow lakes found?
middle or lower course
formation of an oxbow lake?
lateral erosion causes the neck of the meander to narrow. during times of flooding, the high levels of water erode the neck further and the neck is broken. the river now follows the old route through the old straight route of the meander. deposition occurs at the edges of the new straight section- cutting off the old meander - the old meander forms an oxbow lake - separate from the main river
where is a levee found?
lower course
formation of a levee?
water overtops the river banks- causes the velocity of the water to decrease that was previously flowing very fast along the river channel.
causes sediment in suspension to be deposited at the river bank.
coarse, heavier sediment is deposited at the river bank
where are flood plains found?
middle and lower course
formation of a flood plain?
flood- water containing alluvium pouts out over the flat valley floor
the water soaks away, leaving behind the deposited sediment
hundreds of years- flooding forms a thick alluvial deposit- fertile and used for farmers
