Glacial Movement

• Movement of the glacier at its base (more likely to happen in a warm based glacier as basal temperature is more likely to be above pmp)
• Creates melt water -> lubrication (Reducing friction)

Key Mechanisms:

1. Slippage

• Meltwater at base of glacier- can be created by friction at base
• Provides lubrication
• Reduces friction between base of glacier and valley floor
• Glacier slips over valley floor

2. Creep or Regelation

• Regelation- Pressure melts ice, when pressure has passed ice will refreeze
• When? - Obstruction on the valley floor
• Why? EITHER obstruction on valley floor increases pressure on ice at base of glacier. Ice deforms as moves over obstruction [Creep] OR obstruction on valley floor increases pressure on ice at base. Ice melts as PMP is reached and lubrication is increased so ice slides over obstruction. Ice refrezes on other side of obstruction as pressure is released [Regelation]

3. Subglacial bed deformation

• Glacier ice is 'carried' on saturated bed sediments
• Sediments move beneath the glacier due to pressure of ice above
• Usually on gentle gradients

• Common in cold based glaciers as basal slipping is not possible
• Also happens in warm based glaciers as ice deforms 100 times faster at 0°c than at -20°c

Two Types:

• Intergranular Flow- Individual ice crystals re-orientate and then move in relation to one another
• Laminar Flow- Movement of individual layers with glacier. Often linked to annual accumulation layers

On Steep Gradients:

• Ice moves quicker than it can deform
• Ice cracks/fractures -> formation of crevasees
• Extending flow

On Gentle (and negative) Gradients:

• Ice slows and thickens
• Following ice pushes up and over the leading ice
• Compressional Flow

Upper Zone:

• Ice rigid and brittle
• Ice breaks as it moves

Lower Zone:

• Ice is plastic
• Under pressure ice will deform and behave like it is plastic

a) Surface velocity of a glacier

• There is more movement at the centre of the glacier when you move further away from the valley wall. The further you are from the valley wall, the more movement will occur.

b) Changes in velocity with depth

• There is an increase in movement as you get further up into the vertical section through the glacier (200m to 0m). As the distance decreases the amount which the rate of movement increases by decreases.