Lec7: Snow and Ice

Question 1

How thick is the Antarctic ice sheet?

Answer 1

2.5km average, and 4.8km deepest point.

Question 2

What area does the Antarctic ice sheet cover?

Answer 2

14 million km squared.

Question 3

What is the volume of the Antarctic ice sheet, and how much of the world’s freshwater does it hold?

Answer 3

30 million km cubed, holding 68% of world’s freshwater.

Question 4

If the antarctic ice sheet melted, through what process does the Antarctic continent rise another 900m high?

Answer 4

Isostatic rebound = loss of the weight of the ice sheet allows land mass below to rise over thousands of years.

Question 5

Describe the stability of the EAIS compared to the WAIS ice sheet and give reasons.

Answer 5

EAIS = Land mostly above sea level = stable
WAIS = Land mostly below sea level = prone to catastrophic collapse

Question 6

What is catastrophic collapse in terms of the WAIS?

Answer 6

WAIS ice thins. As it floats, it is prone to rapid deglaciation.

Question 7

What was ANDRILL and what did it achieve? Give the names of the two nations, the location they drilled at, the length of the ice core, and how many years it dated.

Answer 7

US and NZ scientists drill into McMurdo ice shelf and retrieve a 1285m long ice core dating 13 million years of history.

Question 8

Describe the layers found in the ANDRILL ice core in relation to ice sheet movement.

Answer 8

1. Ice-sheets thickening = gravel and mud layers

2. Ice-sheets thinning = marine mud and marine sediments layers

Question 9

What three stages does snow go through as it falls, and describe each.

Answer 9

1. Freshly-fallen snow = fluffy + 80% air
2. Firn = layers thicken and experience compression
3. Glacial ice = continuous melting and refreezing

Question 10

What is the max density of glacial ice?

Answer 10

0.92 grams per m cubed.

Question 11

Glacier temperature is warm at the top, then cools throughout the midportion, but then becomes warmest again at the sole. What processes account for this sudden warming?

Answer 11

1. Geothermal heating from basement rock

2. Frictional heat - generated from deformation of ice and glacier flow

Question 12

How is the movement of a glacier measured?

Answer 12

Placing a stake in the snow.

Question 13

Is a glacier serrous or viscous, and does it move downhill or uphill?

Answer 13

Viscous liquid moving downhill.

Question 14

What are the two “types” of glaciers and describe the differences.

Answer 14

1. Warm based (Temperate) - At deep levels, ice reaches pressure melting point and forms meltwater. Also, internal creep (internal plastic deformation) produces meltwater.
2. Cold based (Polar) - frozen to bedrock (doesn’t reach pressure melting point even at deep levels). Only moves by internal creep.

Question 15

Are glaciers faster if….

1. Large or small
2. Coastal or inland (and why?)
3. Steeper or shallower slope?

Answer 15

1. Large
2. Coastal = warmer, produces more meltwater
3. Steeper

Question 16

Describe the movement of ice in terms of outlet glaciers and ice-streams from the center of the EAIS to the ice shelves and seas.

Answer 16

1. Ice flows outwards from center of EAIS (highest point) under gravity
2. Meltwater forms at deep levels, forming ice-streams
3. Strikes transantarctic mountains (acts like a damn)
4. Outlet glaciers squeeze through gaps
5. Outlet glaciers feed Ronne+Filchner and Ross Ice shelves, as well as Ross and Weddell Sea.

Question 17

What are ice-streams?

Answer 17

Fast-flowing channels in the depths of an icesheet.

Question 18

Why does the WAIS accumulate snow and ice faster than the EAIS?

Answer 18

Because it’s surface is ravaged by storms.

Question 19

What are crevasses?

Answer 19

The brittle top layer in an ice sheet cracks.

Question 20

What does glacial erosion do to rocks?

Answer 20

Forms striations from abrasion from glacier flow.

Question 21

If glacier flow continually abrades rocks, what substance forms and what does it do?

Answer 21

Forms rock flour, which gives glacial lakes a blue-green colour.

Question 22

What are moraines, and what are the three types?

Answer 22

Rock debis carried by glacier flow due to glacial erosion.

1. Lateral moraine: debris at edges of glacier
2. Terminal moraine: debris at end of glacier
3. Ground moraine: Left over debris from when glacier melts

Question 23

What is another name for Ground moraine?

Answer 23

Till.

Question 24

What are Sastrugi?

Answer 24

Ridges formed on snow by wind erosion.

Question 25

In what direction are Sastrugi?

Answer 25

Parallel to the direction of the prevailing wind.

Question 26

What are cryncocite holes and why do they form?

Answer 26

Rock debris has higher albedo than surrounding ice, so it heats up and melts through the ice. It eventually stops melting through once it reaches an equilibrium point where heat gained from solar heating equals heat lost to surrounding ice.

Question 27

Are crycocite holes always open to the atmosphere?

Answer 27

No, they can be lidded.

Question 28

What are ice-shelves?

Answer 28

Floating ice sheets attached to coastal glacier.

Question 29

What is the grounding line?

Answer 29

The point at which an ice sheet loses contact with the ground, forming an ice shelf.

Question 30

In what three ways do ice shelves gain mass?

Answer 30

1. Snow falling on surface
2. Freezing of seawater at base
3. Flow of ice from inland to the coast

Question 31

In what two ways do glaciers lose mass?

Answer 31

1. Calving of icebergs.

2. Melting