Glaciation - Unit 3 Flashcards
What are the 2 mechanisms that glaciers can move by?
- Basal sliding
- Internal deformation
What is basal sliding?
Where the whole glacier slides over the underlying bedrock
What is internal deformation?
Where ice crystals deform within the glacier due to stresses acting upon them
Key facts about cold based (polar) glaciers
- Found at high latitudes locations, e.g. Antarctica
- Ice is cold at base = no pressure melting
- Move due to internal deformation
- Slow movement = few metres a year
Key facts about warm based (temperate) glaciers
- Found at low latitudes, e.g. Switzerland
- Average temp = below PMP = pressure melting
- 80-90% movement from basal sliding
- Rapid movement = 20-300m a year
What is pressure melting?
The pressure melting point is the temperature below 0°C at which the ice can melt due to pressure of the overlying glacier ice
What is regelation?
Generation of meltwater from ice that is subjected to higher pressure
What are the 2 specific basal sliding processes?
- Enhanced basal creep
- Regelation slip
Explain enhanced basal creep
- Ice squeezes up against a large bedrock obstacle
- The increase in pressure causes the ice to plastically deform around the feature
Explain regelation slip
- Increasing pressure on upglacier from obstacle causes melting
- Meltwater allows slippage of ice over the obstacle but then refreezes on downglacier side of obstacle
What are the 2 mechanisms that can cause internal deformation?
- Ice creep
- Internal slippage
Explain ice creep
Involves the displacement of ice grains relative to each other
Explain internal slippage
Involves layers of ice within the glacier slipping over each other
What is extensional flow?
- This happens when the gradient of the valley increases, hence making the glacier speed up
- Glacier becomes thinner
What is compressional flow?
- Happens when the gradient of the valley decreases, hence making the glacier slow down
- Glacier becomes thicker
