River Landscapes Flashcards
what is the long profile of a river
the long profile takes the form of a concave curve. the steepest gradient is in the uplands near the source of the river. further downstream, the gradient is reduced
how does the cross profile change throughout the river
The channel becomes wider and deeper with the distance downstream
why does the upper course of the valley be narrow and steep sided
due to vertical erosion by the river combined with weathering and mass movement of the valley slopes
why does the middle course of the valley be wider
due to lateral erosion from meandering rivers
why does the lower course be wide and flat
sediment dumped by the river as it slows down and loses its energy
what is a fluvial process
river process
what are the three types of fluvial process
- erosion
- transportation
- deposition
what is hydraulic action
the power of flowing water to erode the river’s bed and banks
what is solution (the type of erosion)
dissolving of solubles in water such as limestone and chalk
what is traction (type of transportation)
large particles rolled along the river bed by the force of the water
what is saltation (type of transportation)
a bouncing or hopping motion by pebbles too heavy to be suspended
what is suspension (type of transportation)
particles suspended in the water
what is solution (type of transportation)
particles/chemicals dissolved in the water
what landforms result from river erosion
- interlocking spurs
- waterfalls
- gorges
where are interlocking spurs commonly found
in the upper course of the river
why do interlocking spurs occur
there is mostly vertical erosion rather than lateral in the upper course which means that the river is forced to flow around the jutting out pieces of land rather than cutting into them
what two erosion processes erode the plunge pool
- hydraulic action
- abrasion
Characteristics and formation of landforms resulting from erosion – interlocking spurs, waterfalls and gorges.
. - use rivers booklet
how are waterfalls created
- when water flows over hard rock then soft rock, the soft rock erodes faster through hydraulic action and abrasion to form a step
- the step is eroded further and deeper to form a plunge pool, as well as starting to undercut the rock
- the undercut leaves very little support for the hard rock so it cracks and falls into the plunge pool
- the fallen rock is used in abrasion which further erodes the plunge pool
the process repeats and the waterfall recedes upstream
what is a gorge
a steep sided valley where the river once was
how are meanders formed and why are slip off slopes formed
- most water is directed towards the outside of the bend which means it flows faster so had more energy - eroding fast
- the inside bend there fore has less water which means it is shallower, slower and has less energy so it deposits its material
- this builds up over time to form the slip off slope
where are meanders commonly found in a river course
middle and lower course
what are riffles and pools
the shallow and deep areas of a meander respectively
how are oxbow lakes formed
- the neck of the meander narrows due to erosion on opposite sides
- the neck is finally broken through and the water then adopts the shorter route
- deposition occurs at the edges and cuts off the old meander until it is completely separate
what are three landforms that result from deposition
- leveés
- flood plains
- estuaries
how do leveés form
when rivers flood:
- as the water overtops the river banks, there is a sudden localised drop in velocity of the water that had previously been flowing very fast along the river
- this causes sediment in suspension to be deposited at the river bank
- heavier sediment is deposited first and this traps the finer sediment
- with each successive flood the deposited material raises the river banks
what are flood plains and how do they form
- extensive, flat areas land mostly covered by grass
during a flood:
- water containing large quantities of alluvium (river silt) pours out over the flat valley floor
- the water slowly soaks away leaving behind the deposited sediment
- repeated flooding forms a thick alluvial deposit which is fertile and often used for farming
how are estuaries formed
- incoming tides force seawater and sediment up the river channel, mixing with river water flowing in the opposite direction
- where the fresh and salt water meet, velocity falls rapidly resulting in significant deposition
- over time these muddy sediments break the water surface to form extensive mudflats
- vegetation colonises the mudflats to form saltmarshes