River processes produce distinctive landforms.

Question 1

Define: Watershed.

Answer 1

The boundary of a river basin.

Question 2

Define: Confluence.

Answer 2

The point where two rivers meet.

Question 3

Define: Tributary.

Answer 3

A stream that joins a larger river.

Question 4

Define: Source.

Answer 4

The start of a river.

Question 5

Define: Mouth.

Answer 5

Where a river meets the sea.

Question 6

Define: Hydraulic action.

Answer 6

This is the pressure of the water being pushed against the banks and bed of the river. It also includes the compression of air: as the water gets into cracks in the rock, it compresses the air; this puts even more pressure on the cracks and pieces of rock may break off.

Question 7

Define: Corrasion.

Answer 7

Particles carried by the river are thrown against the river banks with considerable force.

Question 8

Define: Corrosion.

Answer 8

This is the chemical reaction between certain rock types and the river water.

Question 9

Define: Solution.

Answer 9

This is the chemical reaction between certain rock types and the river water.

Question 10

Define: Attrition.

Answer 10

This is a process that involves the wearing away of the rocks that are in the river. In the upper course of a river, rocks continually roll around and knock into each other. They chip away at each other until smooth pebbles or sand are formed.

Question 11

Define: Deposition.

Answer 11

This is the layering down of the load of the river.

Question 12

Describe the 3 step process of physical weathering.

Answer 12

1. Water gets into a crack in the rock.
2. As the temperature decreases, pressure is created on the rock by a 9% increase in volume as the water freezes.
3. When the temperature increases again, the crack will have increased in size.

Question 13

Describe the 5 step process of biological weathering.

Answer 13

1. A seed falls into a crack.
2. Rain causes the seedling to grow.
3. Roots force their way into cracks.
4. As the roots grow they break up the rock.
5. Burrowing animals also break up rock.

Question 14

Describe the 3 step process of chemical weathering.

Answer 14

1. Rainwater causes natural acids.
2. Carbonates in limestone are dissolved by weak acids.
3. The cracks in the rock expand.

Question 15

Define: Mass movement.

Answer 15

When material moves down a slope, pulled by gravity.

Question 16

Describe the 5 step process of soil creep.

Answer 16

1. This is the slowest downhill movement.
2. Gravity pulls the water in the soil down a slope.
3. The soil particles will move downhill with the water.
4. Heavy rainfall causes faster downhill movement.
5. The slope appears to have ripples known as terracettes.

Question 17

Describe the 9 step process of slumping.

Answer 17

1. This is common on river banks.
2. A large area of land moves down the slope.
3. Due to the nature of the slip, it leaves behind a curved surface.
4. This is common on clay river banks.
5. During dry weather the clay contracts and cracks.
6. When it rains the water runs into the cracks and is absorbed.
7. The rock becomes saturated.
8. This weakens the rock.
9. Due to the pull of gravity, it slips down the slope on its slip plane.

Question 18

What 8 characteristics are common in the lower course of a river?

Answer 18

1. Mostly deposition.
2. Gentle gradient.
3. Very broad valley.
4. Wider river channel.
5. Deepest river channel.
6. Fastest flowing.
7. Large discharge.
8. Silt and suspended material.

Question 19

What 8 characteristics are common in the middle course of a river?

Answer 19

1. Lateral erosion.
2. Medium gradient.
3. U-shaped valley.
4. Wider river channel.
5. Deeper river channel.
6. Faster flowing.
7. More discharge.
8. Smaller material.

Question 20

What 8 characteristics are common in the upper course of a river?

Answer 20

1. Vertical erosion.
2. Steep gradient.
3. V-shaped valley.
4. Narrow river channel.
5. Shallow river.
6. Slow flowing (because of friction).
7. Small discharge.
8. Large rocks.

Question 21

Define: Interlocking spurs.

Answer 21

Barriers of hard resistant rock, which the river cannot easily erode.

Question 22

Describe the 5 step process of the formation of interlocking spurs.

Answer 22

1. Vertical erosion (in the form of abrasion, hydraulic action and solution) in the river channel results in the formation of a steep sided valley.
2. Over time the sides of this valley are weakened by weathering processes and continued vertical erosion at the base of the valley.
3. Gradually mass movement of materials occurs down the valley sides, gradually creating a v-shape.
4. This material is then gradually transported away by the river when there is enough energy to do so.
5. As the river flows through the valley it is forced to swing from side to side around more resistant rock spurs. As there is little energy for lateral erosion, the river continues to cut down vertically, flowing between spurs of higher land, creating interlocking spurs.

Question 23

What are the 2 features of interlocking spurs?

Answer 23

1. Spurs.

2. V-shaped valley.

Question 24

Define: Waterfalls.

Answer 24

A waterfall is a river or other body of water’s steep fall over a rocky ledge into a plunge pool below.

Question 25

Describe the 6 step process of the formation of a waterfall.

Answer 25

1. A waterfall forms when a river crosses a band of less resistant rock, after flowing over relatively hard, resistant rock.
2. The sudden drop in the river’s course that results is known as a waterfall.
3. The softer rock is cut back more quickly, leaving an overhang of harder rock.
4. Over time, due to the pull of gravity, the harder rock becomes too heavy and falls into the river below.
5. As the water splashes back from the plunge pool, hydraulic action against the back wall of the waterfall also erodes the softer rock.
6. Over time the waterfall moves back or retreats up the valley, forming a gorge.

Question 26

What are the 6 features of waterfalls?

Answer 26

1. Soft rock.
2. Hard rock.
3. Plunge pool.
4. Undercut.
5. Rock lip ready to collapse.
6. Direction of retreat upstream.

Question 27

Define: Meanders.

Answer 27

A winding curve or bend of a river.

Question 28

Describe the 9 step process of the formation of meanders.

Answer 28

1. A meander bend is caused by an increase in lateral erosion.
2. The outside of a meander bend has the deepest water because this is where the greatest erosion takes place and forms a river cliff.
3. The water is moving fastest at this point and therefore erodes the bank using corrasion.
4. The water moves more quickly on the outside due to the lack of friction because of the river’s depth and consequent lack of contact with the bed and banks.
5. A slip-off slope forms on the inside of the meander bend because of deposition.
6. Deposition occurs on the inside because the water is moving more slowly and is shallower.
7. As a result, there is more friction here and the river is less powerful.
8. The river is therefore unable to carry its load and deposition takes place.
9. An underwater current takes some of the eroded material from the river cliff across the river and deposits it on the slip-off slope.

Question 29

What are the 5 features of meanders?

Answer 29

1. Slip-off slope.
2. River cliff.
3. Area of erosion.
4. Area of deposition.
5. Area of fastest flow.

Question 30

Define: River cliffs.

Answer 30

Steep slopes on the outer bend of a river where erosion allows for undercutting.

Question 31

Describe the 3 step process of the formation of a river cliff.

Answer 31

1. Water in the channel moves in a spiral pattern.
2. Water moving along the surface of the river near the outer bank tends to do so at a greater speed than water moving against the inner bank.
3. Thus, the outer bank gets eroded by the force and velocity of the fast moving water, resulting in the formation of a river cliff.

Question 32

What are the 9 features of river cliffs?

Answer 32

1. Inside of bend.
2. Slip-off slope.
3. Deposition.
4. Slow-flowing water.
5. Fast-flowing water.
6. Erosion.
7. Undercutting.
8. Outside of bend.
9. River cliff.

Question 33

Define: Ox-bow lakes.

Answer 33

Crescent shaped lakes lying alongside a winding river.

Question 34

Describe the 9 step process of the formation of an ox-bow lake.

Answer 34

1. An ox-bow lake is formed by continual erosion and deposition of a meander bend.
2. Due to the depth of the water on the outside of the bend, there is less friction with the bed and banks, allowing the water to flow quicker, causing greater erosion.
3. Hydraulic action occurs when the pressure of the river water hits the banks of the meander bend.
4. On the inside of the bend deposition occurs.
5. The water flows slowly here because there is more friction with the bed due to the water being shallower.
6. The ends of the meander bend become closer.
7. The continual erosion on the river cliff and deposition on the slip-off slope cause the ends of the meander bend to come closer.
8. The ends of the meander finally meet. 9. This usually happens during a flood because of the the extra power of the water.

Question 35

What are the 6 main features of ox-bow lakes?

Answer 35

1. Slip-off slope where deposition happens.
2. River cliff where erosion happens.
3. Meander neck.
4. Neck narrows.
5. River cuts through narrow meander neck.
6. Ox-bow lake.

Question 36

Define: Floodplains.

Answer 36

A flat area of land on either side of a river.

Question 37

In what 2 ways can floodplains form?

Answer 37

1. When the river floods.

2. By the migration of meander bends.

Question 38

Describe the 3 step process of the formation of a floodplain when a river floods.

Answer 38

1. When the river holds too much water to stay in its channel, it will flood.
2. The water is shallower on the land than it is in the river and friction increases. The river has less energy and is therefore more likely to deposit the material it is carrying.
3. The water drops the heaviest material and the largest amount on the banks.

Question 39

Describe the 3 step process of the formation of a floodplain by the migration of meander bends.

Answer 39

1. The migration of meander bends across a valley also contributes to the formation of a floodplain.
2. Meanders are formed by lateral erosion, which causes the bend to move across and down the valley in the direction of the river’s flow.
3. The outside of the bend, where erosion is greatest, moves the bend in that direction and the inside bend fills in the floodplain with the deposition that occurs there.

Question 40

What are the 4 main features of a floodplain?

Answer 40

1. Floodplain.
2. River banks.
3. Levee.
4. River channel.

Question 41

Define: Levees.

Answer 41

High banks of the river built up during floods.

Question 42

Describe the 3 step process of the formation of a levee.

Answer 42

1. Every time the river floods it deposits a large amount of material on its banks.
2. This is because there is a change, in speed from the fast flowing water in the channel to the shallower water on the floodplain.
3. Through time these banks or levees build up and help to contain the river within the channel.

Question 43

What are the 3 main features of levees?

Answer 43

1. River channel.
2. Raised bank or levee.
3. Deposited material or alluvium.