4b.1 - Erosion Processes & Landforms

Question 1

How do rivers erode?

Answer 1

Hydraulic Action
Attrition
Abrasion
Corrosion

Question 2

How do rivers transport sediment?

Answer 2

Traction (rolling)
Saltation (bouncing)
Suspension
Solution (Dissolved)

Question 3

How do rivers find the path of least resistance in upland areas?

Answer 3

They flow around the hardest part of the mountain - interlocking spurs

Question 4

Which way do rivers erode in the upper course?

Answer 4

Vertically / downwards

creating v-shaped valleys

Question 5

Where is river flow the fastest?

Answer 5

On the outside of bends

Question 6

Where do you get meanders?

Answer 6

Lower/Middle course
High enough velocity
Less resistant geology

Question 7

How does a meander become an ox-bow lake

Answer 7

The river erodes the outside of the bend fastest
It cuts through the neck of the meander
The new river channel by passes the meander - which dries up, leaving an ox-bow lake

Question 8

Rivers erode laterally to create

Answer 8

A wide, flat, valley floodplain

Question 9

How do meanders get more meander?

Answer 9

Lateral erosion on the outside of the bend
Outer bank undercuts and ‘expands’
Inner bank - deposition of material

Question 10

What is a river cliff

Answer 10

Outside of a meander bend

High velocity of water undercuts the bank

Question 11

What is a point-bar?

Answer 11

Deposited material on the inside of a bend in the river

Question 12

Where do you get a waterfall?

Answer 12

Where hard rock meets sofer less resistant rock

Question 13

How does the waterfall get bigger?

Answer 13

The river undercuts the less resistant rock, leaving the harder rock hanging

Question 14

What is a plunge pool

Answer 14

When a waterfall undercuts hard resistant rock, which collapses and debris swirls around

Question 15

How does a gorge form

Answer 15

The waterfall retreats upstream leaving narrow valley sides behind it

Question 16

How are meanders formed?

Answer 16

Abrasion takes place closer to the outside of the bend (the fastest-flowing part of the channel)

the slowest-flowing water is on inside of bend so deposition
occurs there.

Question 17

Why does river velocity increase downstream?

Answer 17

The channel becomes wider and deeper which reduces the amount of friction.

The channel becomes a more efficient shape (smoother) which means that there is less friction (1).

Tributaries join the main channel which means that there is more water in the river

Question 18

Explain one way the weather and climate can affect river erosion

Answer 18

Global climate change/global warming/rising temperatures,

which increases the amount of evaporation and therefore
reduces erosion

Seasonal variations in rainfall/temperature, which increases discharge during winter months/reduces erosion during summer months

Periods of intense/sustained rainfall will increase erosion

Periods of drought/low rainfall will decrease erosion

Question 19

How do erosional processes lead to waterfalls being formed?

Answer 19

In areas where hard and soft rock overlay, the river is able to erode the softer rock more rapidly creating a waterfall and its associated features: plunge pools and gorges. The soft rock is eroded through a combination of corrasion and hydraulic action.

Question 20

How do erosional processes create V-shaped valley?

Answer 20

Vertical erosion (mainly corrasion) in the upland river can dig deep valleys into the landscape. The exposed sides of these valleys are changed by weathering and mass movement creating a interlocking spurs and a distinctive V-shape valley.

Question 21

How do floodplains form?

Answer 21

‘Migrating’ meanders make the valley floor flat.
When floods occur the floodplain becomes inundated •As the flood waters run out of energy they deposit their silty load leading to the formation of alluvium soil.