Mechanisms of ice movement - Subglacial bed deformation Flashcards
What is subglacial bed deformation?
Subglacial bed deformation is a type of ice movement resulting from the deformation of soft sediment or weak rock beneath the glacier.
Subglacial bed deformation occurs in which type of glaciers?
Subglacial bed deformation occurs in warm based glaciers.
When does subglacial bed deformation take place?
Subglacial bed deformation occurs when a glacier moves over relatively weak or unconsolidated material such as glacial till.
What is deposited subglacial till made up of?
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.
What impact do finer sediments within the glacial till have on overlying ice and why?
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.
What is the result of lower friction between the individual sediment grains?
Friction between individual sediment grains is reduced by the high pore water pressure resulting in the sediment deforming in response to the glaciers weight.
Locally, subglacial bed deformation can account for what percentage of the forward motion of glacier ice?
90%
In polythermal outlet glaciers in Iceland, subglacial bed deformation is responsible for the formation of glaciotectonic sequences. What does this mean?
Glaciotectonic refers to deformations in sediment and bedrock of the Earth’s crust as a consequence of glacier loading, dragging or pushing.