(R) Landforms Flashcards
ox bow lake
- lateral erosion
- when the outside bends of the meander meet causing a straight river
- the old meander dries up
- the bends meet due to continuous undercutting
-middle course
floodplains and levees
- lateral erosion
- it is formed by both erosion and deposition
- erosion caused by meanders makes the plain flat
- levees are embankments along the rivers with a large load
-lower course
meanders
- lateral erosion
- the velocity of the water is greater on the outside bend causing the water to undercut the outside
- on the inner side there is normally a sloping bend as less erosion happens
-middle course
How are V-shaped valleys and interlocking spurs formed?
- vertical erosion (abrasion, hydraulic action, solution) in the river channel
- a steep sided/deep valley forms
- over time the sides of the valley are weakened by weather and vertical erosion
- material (large boulders) move down the valley sides and create a v-shape
- the material is transported away by the river
- as the river flows it has to swing from side to side around more resistant rock outcrops (spurs)
- no energy for lateral erosion
- the river cuts down vertically flowing between spurs of higher land
- creating interlocking spurs and small meanders.
How are floodplains formed?
- both erosion and deposition
- erosion (abrasion, hydraulic action, corrosion) removes interlocking spurs
- a wide, flat area is created on either side of the river
- the height increases over time
- when the river floods material is deposited, increasing the height
- often agricultural land
- they are fertile because they are made up of deposited silt (alluvium)
How does human activity affect the river (channel straightening and dredging)?
the channel is lined with concrete and straightened/deepend
the water has less friction and bends, and flows faster through the area
this reduces the risk of flooding, but it can create problems downstream as more water is sent there
erosion (abrasion and hydraulic action) is increased by the faster flowing water
v shaped valley and interlocking spurs
- the river can’t erode the side slopes of the valley so it flows around them
- this causes interlocking spurs
- they interlock with the other side of the valley
-upper course
waterfall/gorge
- the river erodes vertically
- abrasion and hydraulic action form undercuts
- river flows over different bands of rock, weaker rock is eroded forming a step in the land
- rock in plunge pool erodes causing the step to collapse
-upper course
How are waterfalls and gorges formed?
- natural step in the land
- water flows over the hard rock cap onto the soft rock below
- the water carries a load (rocks)
- causes erosion called abrasion (rocks bash into the rock and break off pieces/wear it down)
- the area below is eroded into a plunge pool
- the force of the water forces air into cracks and widens them, which further erodes the rock
- this is called hydraulic action
- the soft rock behind the waterfall is also eroded
- the rock becomes undercut
- the hard rock cap above is no longer able to support the weight of the water
- it collapses
- this repeats and the waterfall retreats backwards
- forming a gorge (a narrow, steep sided valley)
How are meanders formed?
- the water flows faster at the outside bend of a river (fastest velocity)
- there is less friction because the water is deeper
- there is more energy
- because of this, the water erodes the banks of the outside bend (abrasion, hydraulic action)
- undercutting happens and a river cliff is formed
- the current is slower at the inside bend of the river
- there is more friction because the water is shallower
- there is less energy
- because the flow of the water slows down, the river deposits its load at the inside bend
- this causes a slip-off slope to form
How is an ox bow lake formed?
- overtime, the neck of a meander will become closer together
- when the river floods and bursts its banks, it will break through the meander neck
- the river changes course and takes the easier, straighter path
- this cuts the meander loop off, forming an oxbow lake
- over time, the oxbow lake becomes colonised with vegetation
- it will eventually dry up as it has no supply of water
How are leveés formed?
- when the river floods it deposits its load onto the floodplain
- the lightest material is deposited furthest away from the river
- the heaviest material is deposited closest to the river
- lighter material is more easily carried by the water
- heavier requires more force, the water loses energy and deposits it closer
- over time the material builds up, forming leveés
- this raises the banks of the river
- leveés and floodplains form in the lower course of the river
- they are formed by deposition
What is an estuary?
where the river meets the sea
the river is tidal
when the sea retreats the volume of water in the estuary reduces
when there is less water the river deposits silt which forms mudflats
mudflats are an important habitat for wildlife
deposition increases as the river nears the sea because it spreads out and slows down
the biggest material is dropped first
this causes bars/islands to form in the middle of the main channel
How does human activity affect the river (creating reservoirs)?
reservoirs are formed when a dam is built on a river and the excess water collects behind it
the volume of water in the river can be controlled, reducing the risk of flooding
sediment builds up in the reservoir instead of the river
