GL04 How do glaciers move?

Question 1

What is basal sliding in a glacier?

Answer 1

• Basal sliding is the sliding of a glacier over its rocky base. The sliding is accomplished in three ways: basal slip, enhanced basal creep, and regelation flow.

Question 2

Part of basal sliding

What is basal slip?

Answer 2

• Basal slip occurs when a thin layer of water builds up at the ice-rock interface, and the reduction in friction enables the ice to slide forward.

Question 3

Part of basal sliding

What is enhanced basal creep?

Answer 3

• Enhanced basal creep occurs when ice squeezes up against a large (5-10 m wide) bedrock obstacle, and the pressure causes the ice to plastically deform around it.

Question 4

What is regelation flow?

Answer 4

• Regelation flow occurs when ice presses up against a small bedrock obstacle, and rather than deforming, the ice melts and re-freezes on the lee side where pressure is lower.

Question 5

What is the type of movement exhibited by glaciers?

Answer 5

• Glaciers flow downhill in response to the gravitational forces generated by their weight. Movement can occur by or a combination of three processes: internal deformation, basal sliding, and deformation of soft sediment or weak rock beneath a glacier. The type of movement exhibited by a glacier is closely related to the temperature of the ice.

Question 6

What is internal deformation?

Answer 6

• Internal deformation refers to the slow creep of ice due to slippage within and between the ice crystals. It occurs because individual ice crystals realign themselves within the ice due to the weight of the glacier, and the layers of ice crystals move over each other in a process called laminar flow.
• This process occurs fastest under more stress in the lower layers of a glacier. Internal deformation can occur in both cold-based and warm-based glaciers.

Question 7

What is Bed/Substrate deformation?

Answer 7

• If the glacier rests on clay (or another deformable bedrock), then the sediment may deform under the weight of the ice and the clay then moves under the pressure and friction of the ice.

Question 8

What is the movement of cold-based (polar) glaciers?

Answer 8

• In very cold areas where the relief is usually gentle, cold-based glaciers occur. The base is much colder than the pressure melting point temperature, and so little or no melting occurs.
• These glaciers move mainly by internal deformation.
• Without any reduction of friction or an increase in pressure, there will be no melting. Such glaciers may only move 1-2 cm per day, and erosion will be minimal.

Question 9

How do ice sheets move?

Answer 9

• Ice sheets still move through the same mechanisms as glaciers, except that they are less likely to move by basal sliding as the temperatures are so much colder there.
• The whole ice sheet doesn’t move; instead, there are ‘streams’ of ice movement within the ice sheet.
• These normally follow valleys and other topographic features to transport ice from the centre to the edges, usually ending in ice sheets floating on seawater discharging icebergs.