Formation of Landforms Flashcards
(9 cards)
Formation of waterfall and gorge
The river may flow over an area of hard rock with softer more
easily eroded rock underneath. Over time the softer rock is worn way more rapidly by processes of hydraulic action and abrasion, creating a waterfall.
The water hits the bottom of the falls with great force. This erodes a deep hole called a plunge pool. The softer underlying rock is eroded and
weakened. The softer layer collapses into the plunge pool, undercutting the hard cap rock. The cap rock cracks and then collapses.
Gradually the waterfall retreats upstream, leaving behind a steep sided gorge. Every time the overhanging cap rock breaks off the gorge retreats further and grows longer. There is turbulent fast flowing water in the gorge.
Formation of cave, arch, stack, stump
Firstly, the sea attacks the foot of the cliff and begins to erode areas of weakness such as joints and cracks, through processes of erosion such as hydraulic action, wave pounding, abrasion and solution.
Gradually these cracks get larger, developing into small caves. Further erosion widens the cave and where the fault lines runs through the
headland, two caves will eventually erode into the back of each other forming an arch, passing right through the headland.
A combination of wave attack at the base of the arch, and weathering of the
roof of the arch (by frost, wind and rain), weakens the structure until eventually the roof of the arch collapses inwards leaving a stack, a column of rock which stands separate from the rest of the headland.
The stack continues to erode, eventually collapsing to form a stump which may be covered by water at high tide
Formation of Headland
Because of differences in resistance of rocks to erosion, some parts of the coast may retreat faster than others. This will happen where the
rocks are at right angles to the coastline (a discordant coast). Over thousands of years the softer less resistant rock will be eroded more quickly than the harder more resistant rock and differences become more
pronounced. Eventually there will be headlands that stick out into the sea and bays where the land has been worn back. The headlands are more exposed to wave attack and erosional landforms develop. Due to wave
refraction the energy of the waves is then focused on the headlands and spread out in the bays.
Formation of beaches
Beaches develop at the head, or innermost part, of a bay. In this area wave action is usually not very strong and deposition occurs. The beach
will not extend to the headlands because erosion from waves increases strongly towards the headlands and deeper water. Longshore drift may cause material to be moved along the bay.
Formation of Wave cut platform
The sea attacks the base of the cliff between the high and low water mark along a headland. A wave-cut notch is formed by erosional processes such as
abrasion and hydraulic action. As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face. The backwash carries away the eroded material, leaving a wave-cut
platform. The process repeats. The cliff continues to retreat
Formation of Levee
Levées are long narrow ridges or raised embankments alongside the river. Composed of gravel, stones and alluvium. Steeper on channel side than
land side.
Levées occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.
Sediment that has been eroded further upstream is transported
downstream.
When the river floods, the sediment spreads out across the floodplain. Friction with the land reduces velocity and causes deposition. When a flood occurs, the river loses energy. The largest material (sand
and gravel) is deposited first on the sides of the river banks and smaller material (finer silt and mud) further away.
After many floods, the sediment builds up to increase the height of the river banks, so the levées become higher than the surrounding floodplain.
If a severe flood event occurs, levées may burst and cause serious damage to surrounding land.
Formation of a spit
A spit is a sand or shingle beach that is joined to the land but projects out (downdrift) into the sea.
Longshore drift transports sand along the coast. Direction of prevailing wind determines direction of LSD.
Spits form where the coastline suddenly changes shape or at the mouth of an estuary. Sand or shingle starts to build up in the sheltered lee side of
the headland. This will continue to build up.
Finer material is carried out into the deeper water of the estuary and is deposited as the water loses its capacity to transport it any further.
A spit will continue to grow until the water becomes too deep or until material is removed faster than it is deposited.
The end of the spit may begin to curve round as wave refraction carries material round into the more sheltered water. Wind and waves may also push the spit material back towards the mainland.
The spit will not grow all the way across the estuary as the material is carried seaward by the river
Formation of ox-bow lake
A meander is a winding curve or bend in a river. Water flows fastest on the outer bend of the river where the channel is deeper and there is less
friction. Lateral erosion results in undercutting of the river bank and the formation of a steep sided river cliff. The development of meanders is due to both deposition and erosion. On the inside of the bend, where the river flow is slower, material is deposited on a slip off slope, as there is more
friction. Over time, because of erosion and deposition, meanders gradually
change.
The neck of the meander narrows due to lateral erosion on opposite sides of the meander bend.
During high flow (flood) conditions, the meander neck is broken through.
The river now adopts the shorter (steeper) route, by-passing the old meander.
Deposition occurs at the edges of the new straight section, effectively cutting off the old meander.
The old meander now forms an ox-bow lake, separated from the main river.
Gradually the ox-bow lake silts up to form marshland.
Formation of a meander
The development of meanders is due to both deposition and erosion.
A meander is a winding curve or bend in a river. Water flows fastest on the outer bend of the river where the channel is deeper and there is less friction.
Lateral erosion results in undercutting of the river bank and the formation of
a steep sided river cliff.
On the inside of the bend, where the river flow is slower and water is shallower, material is deposited on a slip off slope, as there is more friction. Over time, because of erosion and deposition, meanders gradually change shape and move across the floodplain and migrate downstream.
