Lesson 8: Glacial Movement Flashcards
Define pressure melting point
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
Temp of PMP?
0 degrees
Effect of PMP on ice melt
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
What is not affected by PMP?
Cold based glaciers (too cold)
How do cold based glaciers move?
Internal deformation
Define inter-granular movement
Individual ice crystals slip and slide over each other
Define intra-granular movement
Ice crystals deform due to stress within the ice and eventually moves downhill under the influence of gravity
How do warm-based glaciers move?
Basal slip
Name 3 processes of basal slip?
Creep and regelation
Extending and compressing flow
Surges
What is basal slip?
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
Describe creep and regelation?
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)
Size of bedrock for creep to occur?
> 1m wide
Size of bedrock for regelation to occur?
<1m wide
Describe extending flow
Over steep gradients, basal slip increases, causing ice to accelerate and thin
Causes the ice to crack creating crevasses
Describe compressing flow
Over small gradients, basal slip decreases, causing ice to decelerate, thicken and compress
Describe surges
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
Describe internal deformation
Weight of the glacier ice and gravity cause the ice crystals to deform, so the glacier moves downslope very quickly
Effect of altitude on basal movement
This affects precipitation and temperature. Greater precipitation and lower temperatures increase the supply of snow and ice, and so its mass balance
Effect of gravity and topography on basal movement
Gravity causes ice to move; the steeper the gradient, the faster it flows
Effect of ice mass/thickness on basal movement
The heavier/greater the mass the greater the pressure in the ice which causes faster movement
Effect of ice temperature on basal movement
Colder ice moves slowly as it does not deform as easily and it stays stuck to the bedrock - PMP not easily reached
Effect of meltwater on basal movement
The more meltwater there is, the faster the movement as basal slippage increases
