Glacial Processes Flashcards
What is the mass balance (budget) of a glacier?
The difference between accumulation (inputs) and ablation (outputs).
What are the 5 key inputs (accumulation) in a glacier?
• Snowfall & precipitation
• Avalanches (snow & rock)
• Meltwater that refreezes
• Wind-blown deposits
• Rock fragments from weathering and erosion
What are the 4 key outputs (ablation) in a glacier?
• Meltwater streams (especially in summer)
• Sublimation & evaporation
• Calving (ice breaking off into lakes/oceans)
• Loss of solar energy due to albedo effect
What is the equilibrium line (firn line) on a glacier?
The point where accumulation = ablation, marking the transition between the accumulation zone and the ablation zone.
What are the 4 factors that affect glacial movement?
• Mass balance: Areas of accumulation move slower than areas of ablation.
• Slope gradient: Steeper slopes result in faster flow.
• Lithology: Softer rocks erode faster, influencing movement.
• Altitude: Higher glaciers have more potential energy but often remain frozen longer.
What is basal slip?
Linked to the pressure melting of ice that takes place along its base
What is regelation creep?
the re-freezing of water under a glacier when pressure reduces after meeting an obstruction.
What is internal deformation?
A movement that is small in scale and takes place in all glaciers, but it is the most common form of movement in cold-based glaciers.
What are the 2 main erosional processes in glaciers?
Plucking and abrasion
How does freeze-thaw weathering contribute to glacial erosion? (Give 2 ways)
• Water enters cracks in rocks, freezes and expands, breaking the rock apart.
• Creates angular debris that glaciers use for abrasion.
What is mass movement?
A source of rock material which falls onto the surface of ice and is incorporated into it.
What are the 2 spatial variations in a glacial budget?
• Upper glacier (accumulation zone): Cold temperatures result in net accumulation.
• Lower glacier (ablation zone): Warmer temperatures lead to net ablation.
What are the 2 seasonal variations in a glacial budget?
• Winter: Net accumulation → glacier expands (positive balance).
• Summer: Net ablation → glacier retreats (negative balance).
Explain how the mass balance works in 3 ways?
If accumulation > ablation, the glacier advances.
If ablation > accumulation, the glacier retreats.
If accumulation = ablation, the glacier is stationary.
Explain in 4 steps how basal slip occurs?
- Ice normally forms from water at a temperature of 0°C, but the temperature at which water freezes is reduced under pressure.
- As a glacier moves it will exert pressure and so some melting may take place at its base.
- A thin film of water then exists between the glacier and the bedrock.
- This film reduces friction, acts as a lubricant, and allows the glacier to slide.
Explain in 2 steps how regulation creep occurs?
- Pressure melting takes place on the upstream side, creating a film of water, and regelation takes place on the downstream side.
- The combination of both processes allows a temperate glacier to slide downhill.
Explain in 2 steps how internal deformation occurs?
- It takes place where the ice crystals set themselves in line with the movement of the glacier and slide past each other.
- Movement can occur along lines of weakness called cleavage planes. This is sometimes called laminar flow.
What is plucking?
If the bedrock beneath a glacier has been weathered in periglacial times, or if the rock is full of joints (well-jointed), a glacier can detach large particles of rock and take them with it. This is called plucking.
What is quarrying?
an extreme form of plucking, creating steep and angular rock cliff faces.
Explain how abrasion occurs in 3 steps?
- Abrasion happens when sharp rock fragments embed themselves in the base and sides of the ice.
- These grind down the bedrock as the glacier moves over the rock like sandpaper, making it smooth and wearing it away.
- This leaves scratches on the rock in the direction of ice movement called striations.
What is crushing?
erosion caused by the sheer pressure exerted by rock fragments embedded at the base of a glacier.
What is basal melting?
abrasion by meltwater, acting under great pressure, at the base of the glacier.
