types of glacier and glacier movement

Question 1

what is a glacier?

Answer 1

Large, perennial accumulation of crystalline ice, snow, rock, sediment + often liquid water that originates on land + moves down slope under influence of own weight + gravity.

Question 2

how do glaciers form?

Answer 2

Called = Diagenesis -> occurs over about 20-40 yrs

fresh snow falls on top of previous yr snow -> they have lots of air pockets (flakes w feathery structure + density of 0.005g/cm3)

Granular snow: each new fall of snow compresses + compacts layer below. Low density ice -> high density

Firn: snow survives 1 summer. Density = 0.4g/cm3

Glacier ice: further compaction. Density = 0.83-0.91 g/cm3

Question 3

Ice sheets

Answer 3

largest accumulation of ice (extending more than 50,000km2) eg Antartica

Question 4

Valley glaciers

Answer 4

confined by valley sides, may be outlet glaciers from ice sheets or fed by snow + ice from one or more corrie glaciers.

Question 5

warm based glaciers usually have..

Answer 5

• high altitude locations
• low latitudes
• steep relief
• basal temps at or above PMP
• rapid rates of movement (20-200m per year) -> largely through basal slippage
  eg Franz Joseph, New Zealand

called temperate glaciers

Question 6

how do warm based glaciers move?

Answer 6

Basal sliding. If basal temp is above or at PMP a thin film of meltwater exists between ice + valley floor = friction reduced.

mobile and fast moving

Question 7

cold based glaciers usually have..

Answer 7

• high latitude locations
• low relief
• basal temp below PMP
• very slow rates of movement as low ablation + accumulation rates

eg commonwealth, Antartica

Question 8

how do cold based glaciers move?

Answer 8

Internal deformation. Two elements ->
intergranular flow : individual ice crystals re-orientate + move in relation to each other
Laminar flow : movement of individual layers within the glacier
Both of these occur when glacier is on a slope. Meserve glacier in antartica moves only 3-4m per yr at its equilibrium + 100% of this movement is internal deformation.

Question 9

what is the PMP?

Answer 9

the temp where ice is on the verge of melting.

Question 10

what factors affect the movement of glaciers?

Answer 10

gravity - mass
Gradient - steeper the faster ice will move
Thickness of ice -> influences basal temp + PMP
Internal temp of ice - movements of one area of ice to another
Glacial budget -> positive budget causes glacier to advance

Question 11

what is the upper zone of a glacier?

Answer 11

where ice is brittle and breaks

Question 12

what is the lower zone of a glacier?

Answer 12

where under pressure the ice deforms

Question 13

what 3 mechanisms does basal sliding consist of?

Answer 13

slippage -> ice slides over valley floor as meltwater reduced friction. Friction itself between moving ice + valley floor -> creation of meltwater

Creep/regelation -> ice deforms under pressure due to obstruction on valley floor -> goes around + over obstruction, before re-freezing when pressure is reduced.

Bed deformation -> ice carried by saturated bed sediments moving beneath it on gentle gradients. Water = high pressure.

Question 14

what is extending flow?

Answer 14

When ice moves over steep slope -> unable to deform quickly enough + fractures, forming crevasses. The leading ice pulls away from ice behind which hasn’t reached steeper slope.

Question 15

what is compressing flow?

Answer 15

When ice thickens + following ice pushes over slower moving leading ice. Planes of movement (slip planes) are at different angles in each case

Question 16

what’s the most important difference between warm + cold based glaciers?

Answer 16

Basal temp and relationship with PMP