River landforms of erosion – waterfalls
Estuary - The tidal mouth of a river where it meets the sea; wide banks of deposited mud are exposed at low tide.
Flood plain - The relatively flat area forming the valley floor on either side of a river channel, which is sometimes flooded.
Gorge - A narrow, steep sided valley, often formed as a waterfall retreats upstream.
Interlocking spurs - A series of ridges projecting out on alternate sides of a valley and around which a river winds its course.
Levees - Embankment of sediment along the bank of a river. It may be formed naturally by regular flooding or be built up by people to protect the area against flooding.
Meander - A pronounced bend in a river.
Oxbow lake - An arc-shaped lake which has been cut off from a meandering river.
Waterfall - Sudden descent of a river or stream over a vertical or very steep slope in its bed. It often forms where the river meets a band of softer rock after flowing over an area of more resistant material
Landforms in upland regions are dominantly created by erosion processes, where land is worn away. Generally, the volume and discharge of rivers in upland regions tends to be low, and the river uses much of its energy in overcoming friction. The erosion direction here is vertical, or straight down into the bed of the river. This has the effect of destabilising the slopes on either side of the river, creating a steep landscape. Waterfalls are one of the most spectacular landforms found in the upper valley and are created by erosion processes.
They occur where a band of hard rock (e.g. granite) overlies a softer rock (e.g. sandstone).
Erosion processes such as Hydraulic Action (the force of the water) and Abrasion (where the river rubs stones that are being transported against the bed of a river thereby breaking it down) dominate. The softer rock is eroded quicker than the harder rock and gradually washes away downstream.
This creates a plunge pool where water is swilled around, potholing can occur here and any rocks and debris swept into the plunge pool by the river will be swirled around and rub against the bed and banks of the plunge pool (called ABRASION), deepening it further.
Over time, the softer rock is eroded further creating an overhang of hard rock. This overhang is unstable as its weight is unsupported.
Eventually, this hard rock collapses because it is unsupported and the waterfall moves back upstream. This creates Gorges, which are steep sided deep river valleys. This process will repeat continually, with the location of the waterfall moving back upstream.
V shaped valleys and interlocking spurs
Vertical erosion also creates V shaped valleys and interlocking spurs. This is shown in the diagram above. In upland valleys the streams are often very small and have LOW DISCHARGE. Up to 95% of energy is used to overcome friction and the rest to erode downwards or vertically via abrasion and hydraulic action. This leaves the sides of river channels steep and unsupported. The sides are also weakened by weathering, and bits slip down into the channel to be washed away by the river. This leaves a V shape. The land has rocks of various resistances. The river winds its way around the more resistant rock and cuts down into the weaker rock, leaving INTERLOCKING SPURS
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