River landscapes and processes

Question 1

What are the three courses of a river?

Answer 1

1. Upper course
2. Middle course
3. Lower course

Question 2

Characteristics of upper course?

Answer 2

1. Steep gradient
2. V-shaped valley
3. Steep sides
4. Narrow, shallow channel

Question 3

Characteristics of middle course?

Answer 3

1. Medium gradient
2. Gently-sloping valley sides
3. Wider, deeper channel

Question 4

Characteristics of lower course?

Answer 4

1. Gentle gradient
2. Very wide, almost flat valley
3. Very wide, deep channel

Question 5

What is the long profile of a river?

Answer 5

1. Shows you how the gradient changes over the different courses.

Question 6

What is the cross profile of a river?

Answer 6

1. Shows you what a cross section of the river looks like.

Question 7

How does verticle erosion alter the cross profile of a river?

Answer 7

1. Verticle erosion deepens the river valley and channel, making it v-shaped.
2. Verticle erosion is dominant in the upper course of a river.
3. High turbulence causes the rough, angular particles to be scraped along the river bed, causing intense downward erosion.

Question 8

How does latural erosion alter the cross profile of a river.

Answer 8

1. This widens the river valley and channel during the formation of meanders.
2. It is dominant in the middle and lower courses.

Question 9

Why is the upper course the way it is?

Answer 9

1. The valley is steep-sided due to verticle erosion and the channel has a steep gradient.
2. The river channel is narrow and shallow - this means discharge is low. The velocity is low due to friction from the rough channel sides and bed.
3. The river carried large, angular stones.

Question 10

Why is the middle course the way it is?

Answer 10

1. The river valley becomes wider due to lateral erosion.
2. The valley sides become gentle slopes and the gradient of the channel is less steep.
3. The river channel becomes wider and deeper.
4. Discharge increases as more streams join the river.
5. The river has a higher velocity as the channel sides are smoother, which leads to less friction.
6. The river’s sediment load is made up of smaller and more rounded rocks as erosion continues.

Question 11

Why is the lower course the way it is?

Answer 11

1. In the lower course, the valley is very wide and flat.
2. The river has a high velocity because there is very little friction from the channel’s smooth sides.
3. It has a large discharge due to more tributaries joining it.
4. The river channel is very wide and deep.

Question 12

Difference between slides and slumps?

Answer 12

1. In slides, material shifts in a straight line.
2. In slumps, material shifts with a rotation.

Question 13

How does geology influence river landforms?

Answer 13

1. Rivers flowing through areas of hard rock have a slower rate of erosion because hard rocks are more resistant, whereas areas with softer rocks will experience more erosion.
2. Landscapes with more resistant rocks tend to have steeper valley sides, landscapes with less resistant rocks tend to have gentle sloping valley sides.

Question 14

How is a waterfall formed?

Answer 14

1. Waterfalls form where a river flows over an area of hard rock followed by an area of softer rock.
2. The softer rock is eroded by hydraulic action and abrasion more than the hard rock, creating a ‘step’ in the river.
3. As water goes over the step it erodes more and more of the softer rock.
4. A steep drop is eventually created, which is called a waterfall.
5. The hard rock is eventually undercut by erosion. It becomes unsupported and collapses.
6. 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.

Question 15

How is a gorge formed from a waterfall?

Answer 15

1. Over time, more undercutting causes more collapses. The waterfall will retreat and leave behind a steep-sided gorge.

Question 16

How are interlocking spurs formed?

Answer 16

1. In the upper course of a river most of the erosion is vertically downwards. This creates steep sided V-shaped valleys.
2. The rivers aren’t powerful enough to erode laterally - they have to wind around the spurs that stick out into their paths on either side.
3. These hillsides are often made of a resistant rock which the river can’t erode, so the river erodes the less resistant rock between the spurs as it winds down the valley.
4. The hillsides that interlock with each other as the river winds around them are called interlocking spurs.

Question 17

What are meanders?

Answer 17

1. Rivers develop large bends called meanders in their middle and lower course, in areas where there are both shallow and deep sections in the channel.

Question 18

How are meanders formed?

Answer 18

1. The current is faster on the outside of the bend because the river channel is deeper. (Less friction to slow the water down)
2. So the outside of the bend is a high-energy environment, meaning more erosion take splace there, forming steep sided river cliffs.
3. The inside of the bend is a low energy environment. The current is slower there because the river channel is shallower (more friction)
4. So eroded material is deposited on the inside of the bend.
5. Over time, this material builds up to form a point bar - a crescent shaped gentle slope made of sand or stones.

Question 19

How are ox-bow lakes formed?

Answer 19

1. Erosion caused the outside bends to get closer.
2. Eventually there’s only a small bit of land left between the bends called the neck.
3. The river breaks through this land, usually during a flood.
4. The river continues to flow along the shortest course.
5. Deposition eventually cuts off the meander.
6. This forms an ox-bow lake.

Question 20

What is a flood plain?

Answer 20

1. Thr flood plain is the wide valley floor on either side of a river which occasionally gets flooded.

Question 21

How is a flood plain made?

Answer 21

1. When a river floods onto the flood plain, the water slows down and deposits the eroded material that it’s transporting. This builds up the flood plain.
2. Meanders migrate across the flood plain, making it wider.
3. Meanders also migrate downstream, flattening out the valley floor.
4. The deposition that happens on the point bars of meanders also builds up the flood plain.

Question 22

How are leeves formed?

Answer 22

1. Leeves are natural embankments along the edges of a river channel.
2. During a flood, eroded material is deposited over the whole flood plain.
3. The heaviest material is deposited closest to the river channel because it gets dropped first when the river slows down.
4. Over time, the deposited material builds up, creating leeves along the edges of the channel.

Question 23

How does climate (rainfall) influence river landscapes?

Answer 23

1. Rivers in wetter climates have a higher discharge because there’s more water entering the channel.
2. Higher discharge increases the rate of erosion - higher volume of water means it has more power to erode the river banks and beds. This adds material to the rivers load.
3. It also shapes the landscape, forming V-shaped valleys in the river’s upper course and a wide, flat flood plain in the lower course.
4. Transporation also increases when a river has a higher discharge because the river has more energy to carry material.
5. Chemical weathering also occurs more in wet climates. Carbonation and dissolution weathering can happen when rainwater comes into contact with minerals that make up the rocks in the river valley. This can make the valley sides more unstable.

Question 24

How does climate (temperature) influence river landscapes?

Answer 24

1. During winter, temperatures can often drop below freezing, especially at night. This leads to more freeze-thaw weathering.
2. In the summer, the higher temperatures speed up the rate of chemical reactions, so chemical weathering tends to increase.
3. This can affect the shape of a river landscape as weathering means mass movements such as rockfalls become more likely, because it loosens material on the valley sides.

Question 25

How can storms affect river processes and landscapes?

Answer 25

1. Storms bring heavy rainfall, which causes the ground to become saturated. This makes it heavier and more unstable. Mass movement is then more likely, river banks my slide or slump into the river channel.
2. Heavy rain can flow quickly over the surface and into a river and the streams that feed into it. This can cause the volume of water in the river to rapidly increase.
3. The high volume of water can increase transportation of material by the river, which can cause more erosion by abrasion and hydraulic action - particularly in the upper course.
4. Duriung storms, the increased volume and velocity of the river can cause it to break through the neck of a meander. Eventually, the meander may be cut off forming an ox-bow lake.
5. Floods caused by storms also build up the flood plain and form leeves.

Question 26

How can droughts affect river processes and landscapes?

Answer 26

1. During a drought, the water volume in a river drops.
2. Less erosion occurs, because lower discharge means that the river has less energy, and is less able to pick up and transport material.
3. Mass movement is also less likely to take place because the land is dry.