Lesson 8: Glacial Movement

Question 1

Define pressure melting point

Answer 1

Ice melts at zero degrees on the surface, but under the weight and pressure of the ice, it can melt at lower temperatures- this is called the PMP

Question 2

Temp of PMP?

Answer 2

0 degrees

Question 3

Effect of PMP on ice melt

Answer 3

Ice can melt at below 0°C, allowing the ice to move with the help of melt water even if the air temperature is below freezing point

Question 4

What is not affected by PMP?

Answer 4

Cold based glaciers (too cold)

Question 5

How do cold based glaciers move?

Answer 5

Internal deformation

Question 6

Define inter-granular movement

Answer 6

Individual ice crystals slip and slide over each other

Question 7

Define intra-granular movement

Answer 7

Ice crystals deform due to stress within the ice and eventually moves downhill under the influence of gravity

Question 8

How do warm-based glaciers move?

Answer 8

Basal slip

Question 9

Name 3 processes of basal slip?

Answer 9

Creep and regelation
Extending and compressing flow
Surges

Question 10

What is basal slip?

Answer 10

Occurs when the base of the glacier is at the PMP, which means that meltwater is present and acts as a lubricant, enabling the glacier to slide more rapidly over the bedrock

Question 11

Describe creep and regelation?

Answer 11

When the structure of the ice changes to move around an obstacle. Under pressure the ice may plastically deform around an obstacle (creep) or under lots of pressure it will melt (PMP) and refreeze the other side of the obstacle. (regelation)

Question 12

Size of bedrock for creep to occur?

Answer 12

> 1m wide

Question 13

Size of bedrock for regelation to occur?

Answer 13

<1m wide

Question 14

Describe extending flow

Answer 14

Over steep gradients, basal slip increases, causing ice to accelerate and thin
Causes the ice to crack creating crevasses

Question 15

Describe compressing flow

Answer 15

Over small gradients, basal slip decreases, causing ice to decelerate, thicken and compress

Question 16

Describe surges

Answer 16

Suddenly a glacier can advance rapidly, sometimes 100 times faster than normal. There can be many cause such as earthquakes but the most common is increased basal sliding from the build up of meltwater at the ice-rock interface

Question 17

Describe internal deformation

Answer 17

Weight of the glacier ice and gravity cause the ice crystals to deform, so the glacier moves downslope very quickly

Question 18

Effect of altitude on basal movement

Answer 18

This affects precipitation and temperature. Greater precipitation and lower temperatures increase the supply of snow and ice, and so its mass balance

Question 19

Effect of gravity and topography on basal movement

Answer 19

Gravity causes ice to move; the steeper the gradient, the faster it flows

Question 20

Effect of ice mass/thickness on basal movement

Answer 20

The heavier/greater the mass the greater the pressure in the ice which causes faster movement

Question 21

Effect of ice temperature on basal movement

Answer 21

Colder ice moves slowly as it does not deform as easily and it stays stuck to the bedrock - PMP not easily reached

Question 22

Effect of meltwater on basal movement

Answer 22

The more meltwater there is, the faster the movement as basal slippage increases