1c. Different types of glacier and movement

Question 1

How is glacial ice formed?

Answer 1

• snow fall remains frozen throughout year
• fresh snow fall on top, low density, feathery texture
• new snowfall compresses previous layers (neve), forcing out air, becomes higher density ice
• if ice survives one summer, its called firn
• further compaction by snow forms glacial ice (process called diagenesis)

Question 2

What colour is glacial ice and why?

Answer 2

bluish because of the lack of air in the ice

Question 3

How long does it take for glacial ice to form?

Answer 3

40-1000 years

Question 4

What is an ice sheet? (size?)

Answer 4

large accumulations of ice extending 50,000km²

Question 5

Where are the only 2 current ice sheets?

Answer 5

• Greenland
• Antarctica (13.6 million km²)

Question 6

What is a valley glacier?

Answer 6

Glacier confined by valley walls, between 10-30km in length

Question 7

Characteristics of warm-based (temperate) glaciers?

Answer 7

• high altitude locations
• steep relief
• basal temperature at or above pressure melting point (creates layer of meltwater, reducing friction, helps movement)
• rapid rates of movement

Question 8

Impact of warm-based glaciers on the landscape?

Answer 8

• rapid rates of movement cause erosion/erosional landforms
• ablation produces meltwater, causing glacio-fluvial landforms

Question 9

Characteristics of cold-based (polar) glaciers?

Answer 9

• high latitude locations
• low relief
• basal temperatures below pressure melting point so frozen to bedrock (slow movement plucks valley floor)
• very slow rates of movement, few metres per year

Question 10

Impact of cold-based glaciers on the landscape?

Answer 10

Limited impact, not very dynamic glaciers

Question 11

Diagram of glacier temperature profiles

Answer 11

-

Question 12

What’s the most important difference between warm and cold based glaciers?

Answer 12

Relationship between the basal temperature and the pressure melting point

Question 13

Glacial movement: factors that influence movement?

Answer 13

• Gravity
• Gradient
• thickness of ice (influences basal temp & pressure melting point)
• glacial budget (+=advance)
• internal temp of ice

Question 14

What is the rigid zone of the glacier?

Answer 14

where ice is brittle and breaks, shown as crevasses

Question 15

What is the zone of plastic flow?

Answer 15

where, under pressure, the ice deforms and behaves more like plastic

Question 16

Why do the sides and base of glaciers move slower than the middle and top?

Answer 16

• ice may have been frozen to sides and valley floor
• obstructions - friction

Question 17

Basal sliding: which type of glacier? how does it happen?

Answer 17

• warm based (temperate) glacier
• basal temp is above pressure melting point, thin layer of meltwater exists between glacier and valley floor, reduces friction

Question 18

What 3 mechanisms does basal sliding consist of?

Answer 18

• slippage
• bed deformation
• creep/regualtion

Question 19

Basal sliding: slippage?

Answer 19

Ice slides over valley floor as the meltwater reduces friction between the base of glacier and valley floor (any friction can create more meltwater)

Question 20

Basal sliding: creep or regelation?

Answer 20

• When ice deforms under pressure due to obstructions on valley floor - Spreads around/over obstruction before refreezing when pressure is reduced

Question 21

Basal sliding: bed deformation

Answer 21

When the ice is carried on saturated bed sediments that move along with the glacier (high pressure)

Question 22

Internal deformation: what type of glacier? What type of relief does it happen on?

Answer 22

• cold based (polar) glaciers
• only occurs on a slope

Question 23

Internal deformation: what two types of flows and how do they work?

Answer 23

• inter-granular flow = movement of individual ice crystals in relation to each other
• laminar flow = movement of individual layers within the glacier

Question 24

Internal deformation: how does it create crevasses?

Answer 24

• when ice moves over a steep slope, it can’t deform fast enough so it fractures - forms crevasses
• forms slip planes

Question 25

Internal deformation: how does an extending flow create crevasses?

Answer 25

• down slope, leading ice pulls away from ice behind it that hasn’t reached the slope yet

Question 26

Internal deformation: compressing flow

Answer 26

• when gradient reduces, ice thickens and pushes over slower moving leading ice