Water on the Land Flashcards
What is hydraulic action?
The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
What is abrasion?
Rocks carried along by the river wear down the river bed and banks.
What is attrition?
Rocks being carried by the river smash together and break into smaller, smoother an rounder particles.
What is solution?
Soluble particles are dissolved into the river?
What are the four types of transportation?
Solution, suspension, saltation and traction.
What is transportation by solution?
Minerals are dissolved in the water and carried along in a solution.
What are the four ways rivers erode?
Hydraulic action, abrasion, attrition and solution.
What is transportation by suspension?
Fine light materials are carried along in the water.
What is transportation by saltation?
Small pebbles and stones are bounced along the river bed.
What is transportation by traction?
Large boulders and rocks are rolled along the river bed.
What are the three types of weathering?
Physical, chemical and biological.
What is physical freeze thaw weathering?
Water gets into cracks in rocks. Normally at night time when temperatures drop, the water freezes and expands causing the cracks further apart. This process is repeated until a piece of rock falls off.
How does wind, rain and waves cause physical weathering?
The wind can blow tiny grains of sand against the rock, weathering it. Rain and waves can also weather rocks over time.
What is biological weathering?
When animals and plants wear away at rocks.
Give two examples of biological weathering?
Rabbits burrow into the cracks in rocks and break them.
Plant roots grow through the cracks in rocks and break them apart.
What is chemical weathering?
When rocks are worn away by chemicals.
Give an example of chemical weathering?
Acid rain reacts with rocks to wear them away.
What is deposition?
Deposition is when the river drops the eroded material it has been transporting. This happens when a river slows down and loses velocity.
Why do rivers slow down and deposit material?
The volume of water in the river decreases.
The amount of eroded material increases.
The water is shallower.
The river reaches its mouth.
What is the course of a river?
The path of a river as it flows downhill.
What is a channel?
The part of the river valley occupied by water itself.
What is the long profile of a river?
Shows you how the gradient changes over the different courses.
What is the cross profile?
Shows you a cross section of what the river looks like.
What are the characteristics of the upper course of a river?
Steep gradient, v-shaped valley, steep sides and a narrow and shallow channel.
What are the characteristics of the middle course of the river?
Medium gradient, gently sloping valley sides and wider and deeper than the upper course.
What are the characteristics of the lower course of the river?
Gentle gradient, very wide almost flat valley and a very wide deep channel.
What takes place in the upper course?
Vertical erosion, hydraulic action, abrasion, attrition, some traction and saltation at high flow, deposition of large material and large load.
What takes place in the middle course?
Some vertical erosion but lateral erosion is more important, hydraulic action is less important, suspension is the main type of transport but saltation and traction is still present, deposition is more obvious and load size is smaller.
What takes place in the lower course?
Only a small amount of lateral erosion, erosion is much less important, suspension is the dominant transportation type, deposition of fine material and large amount of small load.
What is vertical erosion?
This deepens the river valley and channel making it v-shaped. Mainly dominant at the upper course of a river.
What is lateral erosion?
This widens the valley and channel. It is dominant at the middle and lower course of the river.
What is a waterfall?
The sudden and often vertical drop of a river along its course.
What is needed for a waterfall to form?
Vertical erosion, high volume of water and a layer of hard rock covering softer rock
How does a Waterfall form? Use diagrams.
Waterfalls form where a river flows over an area of hard rock followed by an area of softer rock. The softer rock is eroded more than the hard rock, creating a step in the river. As water goes over the step it erodes more and more of the softer rock.
A steep drop is eventually created, which is called a waterfall.
The hard rock is eventually undercut by erosion. It becomes unsupported and collapses. The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock by abrasion. This creates a deep plunge pool. Over time, more undercutting causes more collapses. The waterfall will retreat, leaving behind a steep sided gorge.
How does an ox-bow lake form?
As the outer banks of a meander continue to be eroded through processes such as hydraulic action the neck of the meander becomes narrower. Eventually due to the narrowing of the neck, the two outer bends meet and the river cuts through the neck of the meander. The water now takes its shortest route rather than flowing around the bend.
Deposition gradually seals off the old meander bend forming a new straighter river channel. Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake. Over time this feature may fill up with sediment and may gradually dry up except for periods of heavy rain. When the water dries up, the feature left behind is known as a meander scar.
Where are waterfalls found?
At the upper course of a river.
Where are ox-bow lakes found?
At the middle and lower course of a river.
What is a meander?
A large bend in a river course.
How do meanders form?
The current is faster on the outside bend because the water is deeper, meaning there is less friction to slow the river down. So more erosion takes place on the outside of a bend forming a river cliffs. The current is slower on the inside of the bend because the river channel is shallower, meaning more friction. So eroded material is deposited on the inside of the bend, forming slip-off slopes.
