P1 River Landscapes Flashcards
How does the long profile of the river change from source to mouth?
The gradient decreases
What landforms are often in the upper coarse of a river?
Interlocking spurs, v shaped valley
What landforms are often in the middle coarse of a river?
Meanders, oxbow lakes
What landforms are often in the lower coarse of a river?
Levees, floodplain,estuaries
What is erosion and how does it work differently in the different courses of the river?
Erosion : the process of breaking down and removing sediment/washing away material
Upper coarse :vertical as the river is flowing faster (bed erosion)
Middle: Lateral as gradient is less steep (bank erosion)
Describe the process of hydraulic action
.river banks have cracks and crevices
.the flow of the river forces air inside cracks
.air inside the cracks is compressed and it expands
.this puts pressure on the river bed causing the cracks to widen and make the bank more unstable
.parts of the bank break away
(Active at the foot of waterfalls and on outside bends of meanders)
Describe the process of attrition
.rocks knock together with force
.rocks gradually become smaller, smoother and rounder
Describe the process of abrasion
.rocks carried by the river are moved towards the river banks and bed
.the rocks scrape along the banks and bed, eroding it
Describe the process of solution
.river water is slightly acidic due to absorption of CO2 and humid acid from vegetation
.carbonate rocks such as limestones dissolve
.eventually rocks dissolve completely into the river water
What is traction?
Large particles are rolled along he river bed by the force of the water at times of high discharge
What is saltation
Small rocks and sand particles are bounced along the river bed (as they are too heavy to be suspended)
What is suspension?
Finer/lighter clay and sand particles are carried along suspended in the water even at low discharges
What is solution
Some minerals dissolve(such as calcium carbonate) and are carried by the water, this requires very little energy
What is load?
Material being transported by a river is called its load
When does deposition occur?
When the velocity of a river slows -decreasing the energy of the water
Where does deposition occur?
At a floodplain, where river meets larger source of water (eg sea)
Why does deposition occur at floodplains?
When a river floods, friction with the land slows water down causing it to deposit its load and lose energy
Why does deposition occur at meanders?
As water swings around the bend friction causes the water to go slower on the inside of the bend and it goes faster on the outside. This causes deposition on the inside of the slope.
Why does deposition occur at the river mouth?
Tidal influences slow river down, the water loses energy, deposits material
How do interlocking spurs form?
.vertical erosion of river bed occurs deepening the v-shaped valley
. Harder rock is harder for the river to erode so it winds its way around the harder rock and eordes the softer rock behind it therefore creating interlocking spurs
How does a waterfall form?
.water runs over alternating bands of hard rock on top of the soft rock beneath it.
.erosion will start to break down rocks through the process of abrasion, hydraulic action and solution
.hydraulic action wears away the soft rock as water runs over it becuas it is less resistant than the hard rock above it.
.over time the soft rock starts to undercut the hard rock
.the hard rock is left unsupported and as a result of this it collapses into the river bed
.rocks that have fallen are either transported away or scrape away the river bed trough the process of erosion . This coupled with continuous friction of water, a dent in the river bed starts to form. This is called a plunge pool
How are gorges formed?
By waterfalls retreating,as erosion continues
Characteristics of meanders?
.slip off slope on the inside of a bend: caused by deposition
. River cliff on the outside of bend: caused by lateral erosion and undercutting
. Deposition on inside, erosion on outside
How does an oxbow lake form?
.water flows over land, water swings round to the outside of the river where there is less friction
. As the river erodes the river bank a bend starts to form known as a meander
.on the inside of the bend the flow is slower resulting in deposition
.the neck of the river grown narrower
.when the neck of the river breaks through the water will take the shortest route and take the straight course
.the neck become sealed off altogether as a result of deposition.
What is a levee?
An embankment of sediment along a river bank. Can be formed naturally or by regular flooding or man made as flood protection
