4.6 Landscapes Flashcards
What is meant by the long profile of a river?
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The long profile of a river shows changes in the height (altitude) of the course of a river from its source to its mouth.
How does the river Eden’s landscape change along its long profile
Near the source of a river there is more vertical erosion as the river flows downhill, using its energy to overcome friction. As a result the channels are narrow and shallow and may contain large boulders and angular fragments eroded and weathered from the steep valley sides. The sediment in the river creates turbulence and friction.
Compare hydraulic action with abrasion
Hydraulic action is the erosion that occurs when the motion of water against a rock surface produces mechanical weathering. Whereas Bits of rock and sand in waves grind down cliff surfaces like sandpaper.
Define weathering
wear away or change the appearance or texture of something by long exposure to the atmosphere.
Compare freeze thaw and biological weathering
Biological weathering is the weakening and subsequent disintegration of rock by plants, animals and microbes. Growing plant roots can exert stress or pressure on rock whereas Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart.
Compare traction with suspension transport
Traction is large boulders and rocks are rolled along the river bed. Whereas traction is fine light material is carried along in the water.
Explain the stages and processes responsible for waterfall formation
Waterfalls often form in the upper stages of a river where it flows over different bands of rock. It erodes soft rock more quickly than hard rock and this may lead to the creation of a waterfall.
The soft rock erodes more quickly, undercutting the hard rock.
The hard rock is left overhanging and because it isn’t supported, it eventually collapses.
The fallen rocks crash into the plunge pool. They swirl around, causing more erosion.
Over time, this process is repeated and the waterfall moves upstream.
A steep-sided gorge is formed as the waterfall retreats.
How is a v shaped valleys formed
When a river is near its source, it often develops a V-shaped valley as the river erodes down (this is called vertical erosion). At the same time, weathering breaks up material on the valley slopes. Weathered material from the valley sides gets deposited in the river. This material is carried by the river and erodes the riverbed through abrasion.
Meanders and ox-bow lakes formation
A meander is a bend in the river. Meanders usually occur in the middle or lower course, and are formed by erosion and deposition. As the river flows around a meander, centrifugal forces cause the water to flow fastest around the outside of the bend. This creates erosion on the outside and deposition on the inside of the bend, which means that the meander slowly moves. If the meander moves so much that the bend becomes very large, the course of the river may change. The meander may be cut off and deposition fills the section that no longer flows. This forms an ox-bow lake.
Delta formation
A river carrying sediment reaches the sea or a lake.
It loses energy and deposits material.
The sediment may be sorted as the heaviest material is deposited first.
Over time, more and more sediment is added.
If the tides are strong enough the sediment will be washed away. If not, it will build up a land mass (delta) at the mouth of the river.
two ways climate, geology and slope processes change the river
landscape
Can make waterfalls The river flows over bands of softer and harder rocks.
Softer rock is more quickly eroded.
The river undercuts the harder rock leaving an overhang.
The river forms a plunge pool below the waterfall.
Overhanging rock is unsupported and falls into the plunge pool.
Or v shaped valleys
Rivers begin high up in the mountains so they flow quickly downhill eroding the landscape vertically.
The river cuts a deep notch down into the landscape using hydraulic action, corrasion and corrosion.
As the river erodes downwards the sides of the valley are exposed to freeze-thaw weathering which loosens the rocks (some of which will fall into the river) and steepens the valley sides.
The rocks which have fallen into the river help the process of corrasion and this leads to further erosion.
The river transports the rocks downstream and the channel becomes wider and deeper creating a V-shaped valley between interlocking spurs.
