Mechanisms of ice movement - Subglacial bed deformation

Question 1

What is subglacial bed deformation?

Answer 1

Subglacial bed deformation is a type of ice movement resulting from the deformation of soft sediment or weak rock beneath the glacier.

Question 2

Subglacial bed deformation occurs in which type of glaciers?

Answer 2

Subglacial bed deformation occurs in warm based glaciers.

Question 3

When does subglacial bed deformation take place?

Answer 3

Subglacial bed deformation occurs when a glacier moves over relatively weak or unconsolidated material such as glacial till.

Question 4

What is deposited subglacial till made up of?

Answer 4

Deposited subglacial till is made up of poorly sorted sediments ranging from boulders to clay, and till sequences can be up to tens of meters thick.

Question 5

What impact do finer sediments within the glacial till have on overlying ice and why?

Answer 5

The finer sediments within the till are not cohesive and the weight of the ice, together with a high pore water pressure inside the sediment, increased by glacial meltwater at the ice/bedrock interface, displaces the overlying ice.

Question 6

What is the result of lower friction between the individual sediment grains?

Answer 6

Friction between individual sediment grains is reduced by the high pore water pressure resulting in the sediment deforming in response to the glaciers weight.

Question 7

Locally, subglacial bed deformation can account for what percentage of the forward motion of glacier ice?

Answer 7

90%

Question 8

In polythermal outlet glaciers in Iceland, subglacial bed deformation is responsible for the formation of glaciotectonic sequences. What does this mean?

Answer 8

Glaciotectonic refers to deformations in sediment and bedrock of the Earth’s crust as a consequence of glacier loading, dragging or pushing.