Formation of hydrosphere Flashcards
Formation of a waterfall
Soft rock is undercut. This leaves a layer of hard rock
which overhangs the layer of soft rock.
The water flows over the overhang and creates a plunge pool in the soft rock below. As the water hits the plunge pool
it will erode it by both hydraulic action (the force of the water against the bedrock) and by corrasion (where the material
carried by the river acts like sandpaper against the riverbed). Eventually, the overhang will collapse due to the
erosion of the soft rock beneath it. The waterfall then retreats upstream. This creates a steep, gorge-like valley. For example, Falls of Clyde.
Formation of a meander
Meanders form in relation to riffles and pools (deeper solutions). This causes the river current to move from side to side as a helicoidal flow. As the river makes its way to the middle course, it gains more water and therefore more energy. Lateral erosion starts to widen the river. When the river flows over flatter land they develop large bends called
meanders. As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed
and therefore increased erosion through hydraulic action - when pressure from the water causes cracks in the rock to widen and corrasion, when pebbles move along the river bed, having a sand-papering effect. The lateral erosion on the outside bend causes undercutting of the bank to form a river cliff. Water on the inner bend is slower, causing the water to slow down and deposit the eroded material, creating a
gentle slope of sand and shingle. The build-up of deposited sediment is known as a slip-off slope (or sometimes river beach).
Formation of a oxbow lake
Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period
of time. Erosion narrows the neck of the land within the meander and as the process continues, the meanders move
closer together. When there is a very high discharge (usually during a flood), the river cuts across the neck, taking a
new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped
oxbow lake.
Formation of a V-shaped valley
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.
