OCR A Level GL - 4 OCR A Level GL 2.1c Glacier Types and Movement

Question 1

How does glacial ice form?

Answer 1

Snow falls on previously fallen snow, many layers build up and the bottom layers are compacted squeezing air out, turning into granular snow and firn and then glacial ice

Question 2

What is firn/névé?

Answer 2

Compacted granular ice that forms where snow is deeply buried.

Question 3

What is the density of fresh snow?

Answer 3

0.05 g/cm3

Question 4

What is the density of firn/névé?

Answer 4

0.4 g/cm3

Question 5

What is the density of glacial ice?

Answer 5

between 0.83 and 0.91 g/cm3

Question 6

What is diagenesis?

Answer 6

the process whereby fresh snow, over time, under compaction, becomes glacial ice.

Question 7

How long does it take for glacial ice to form?

Answer 7

between 30-40 years in high altitude locations up to 1,000 years in high latitude locations

Question 8

What are the two main types of glaciers?

Answer 8

1. Valley glaciers 2. Ice sheets

Question 9

What are the characteristics of valley glaciers?

Answer 9

They follow the course of existing river valleys Typically between 10-30km in length

Question 10

What are the characteristics of ice sheets?

Answer 10

They are the largest accumulations of ice Defined by extending more than 50,000km2 Antarctica and Greenland are the only 2 ice sheets

Question 11

What is the pressure melting point?

Answer 11

The temperature at which ice is on the verge of melting

Question 12

What are the characteristics of warm-based glaciers?

Answer 12

1. High altitude locations e.g. Alps and Rockies 2. Steep relief 3. Basal temperature at or above pressure melting point 4. Rapid rates of movement (typically between 20-200m/year)

Question 13

What are the detailed warm-based glacier characteristics

Answer 13

Warm-based glaciers occur in temperate areas e.g. western Norway and southern Iceland​ Small (hundreds of metres to a few kilometres in width)​ There is summer melt​ Meltwater lubricates the glacier, leading to more movement (20 - 200m per year) and consequently more erosion, transportation and deposition​ All ice in warm-based glaciers is at or above pressure melting point because of the warmer atmospheric temperature, the weight of ice and the effect of geothermal heat at the bed​ Warm-based glaciers are associated with basal processes such as basal sliding. These promote more rapid ice flow and lead to the development of specific features such as striations and the formation of subglacial landforms (e.g. drumlins) and glaciofluvial features (e.g. eskers). ​

Question 14

What are the characteristics of cold-based glaciers?

Answer 14

1. High latitude locations e.g. Greenland and Antarctic 2. low relief 3. Basal temperature below pressure melting point and so frozen to the bedrock 4. Very slow rates of movement (only a fewm/year)

Question 15

What are the detailed characteristics of cold-based glaciers?

Answer 15

Cold-based glaciers occur in polar areas, e.g. the Arctic and Antarctic. ​ They are large, cover hundreds of square kilometres.​ They occur in areas of low precipitation and little snow. Therefore, there are low levels of accumulation and little to no melting as the ice stays very cold​ All ice in cold-based glaciers is below pressure melting point.​ There is very little meltwater and therefore, slow movement (only a few metres/yr). ​ The glacier is often frozen to the bed of the glacier, meaning less erosion, transport and deposition.​ Cold-based glaciers have limited landscape impacts. ​

Question 16

How does gravity influence the movement of glaciers?

Answer 16

it is the fundamental cause of glacial movement

Question 17

How does gradient influence the movement of glaciers?

Answer 17

the steeper the gradient of the ground, the faster ice will move

Question 18

How does thickness of ice influence the movement of glaciers?

Answer 18

thickness influences the basal temperature and therefore the pressure melting point, which influences movement

Question 19

How does internal temperature of ice influence the movement of glaciers?

Answer 19

It determines the type of movement Internal Deformation OR Basal Sliding This will affect the speed of movement

Question 20

How does glacial budget influence the movement of glaciers?

Answer 20

a positive budget causes glacial advance

Question 21

What are the two mechanisms by which internal glacial ice moves?

Answer 21

1. break apart (creating crevasses)
2. internal deformation

Question 22

Which part of the glacier moves the fastest?

Answer 22

centre of a glacier at the surface

Question 23

What are the characteristics of the rigid zone in a glacier?

Answer 23

1. Found in the upper zone of a glacier
2. Ice is solid, brittle and breaks
3. Crevasses form

Question 24

What are the characteristics of the zone of plastic flow in a glacier?

Answer 24

1. Found in the lower zone of a glacier, where ice is under pressure
2. . Ice will deform and behave more like a plastic

Question 25

What is basal sliding?

Answer 25

the act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant

Question 26

What 3 types of basal sliding?

Answer 26

1. Slippage
2. Creep​
3. Bed deformation

Question 27

What is slippage?

Answer 27

a circular motion that can cause ice to move away from the back wall of a hollow​

Question 28

What is creep?

Answer 28

a slow, downward movement of loose rock and soil down a gentle slope​

Question 29

What is bed deformation?

Answer 29

the movement of soft sediment or weak rock beneath a glacier.

Question 30

When is bed deformation most effective?

Answer 30

beneath temperate glaciers as the underlying sediment and rock are saturated with water

Question 31

Give a named example of the importance of basal sliding in glacial movement?

Answer 31

Franz Josef glacier in New Zealand -which is a warm based glacier that moves approximately 300m per year, and 45% of its movement is from basal sliding

Question 32

What are the 2 types of internal deformation?

Answer 32

1. Intergranular flow
2. . Laminar flow

Question 33

What is intergranular flow?

Answer 33

When individual ice crystals re-orientate and move in relation to each other

Question 34

What is laminar flow?

Answer 34

where individual ice crystals move along layers within the glacier, often within layers of annual accumulation

Question 35

Give a named example of glacial movement by internal deformation

Answer 35

The Meserve glacier in Antarctica moves only 3-4m per year and 100% of this movement is by internal deformation.

Question 36

What is extending flow?

Answer 36

It is when ice moves over a steep slope and it is unable to deform quickly enough so fractures and creates crevasses. The leading ice pulls away from the ice behind it which has yet to reach the steeper slope

Question 37

What is compressing flow?

Answer 37

It is when the gradient reduces and ice thickens. The following ice pushes over the slower moving leading ice, on planes of movement, which are all at different angles