Welcome to Glacier Systems!
In this chapter, we are going to look at glaciers not just as big blocks of ice, but as active systems. Think of a glacier like a living thing—it breathes, moves, and changes depending on the weather. We will explore how glaciers stay in balance, how they manage to move huge distances, and what happens in the freezing areas surrounding them (periglacial zones).
Understanding these processes is key to Topic 2 because it explains why our landscapes look the way they do today. Whether you are aiming for an A* or just trying to get your head around the basics, these notes will break everything down step-by-step.
1. The Glacier as a System
In Geography, a system is just a way of looking at how things move in and out of a place. A glacier is an open system, which means it has energy and matter (ice and water) entering and leaving it.
The Three Parts of the System:
- Inputs: These are things "added" to the glacier. The main input is snow (which turns into ice), but it also includes avalanches and debris falling onto the ice.
- Processes (Stores and Transfers): This is how the ice moves or stays still. This includes glacial movement and the storage of water as ice.
- Outputs: These are things "leaving" the glacier. The most common is meltwater. Other outputs include evaporation and calving (when big chunks of ice break off into the sea).
Quick Analogy: Think of a glacier like a bank account. Snow is your "income" (input). The ice is your "savings" (store). Melting is your "spending" (output).
2. Glacial Mass Balance
Mass Balance is the "budget" of the glacier. It tells us whether the glacier is growing or shrinking over a year. We measure this using a simple equation:
\(Net Balance = Accumulation - Ablation\)
Key Terms to Remember:
- Accumulation: When the glacier gains snow and ice (usually at the cold, high-altitude top).
- Ablation: When the glacier loses ice through melting or calving (usually at the warmer, lower-altitude bottom).
- The Equilibrium Line: The "sweet spot" in the middle where accumulation and ablation are exactly equal.
What happens when the balance changes?
- If \(Accumulation > Ablation\), the glacier has a positive mass balance and it will advance (grow longer).
- If \(Ablation > Accumulation\), the glacier has a negative mass balance and it will retreat (get shorter).
Did you know? Even when a glacier is "retreating," the ice is still moving forward downhill! It just means the snout (the front) is melting faster than the ice can replace it.
Quick Review: Mass Balance
Positive Balance = Advance (Winter/Colder climate)
Negative Balance = Retreat (Summer/Warmer climate)
3. How Glaciers Move
Glaciers might look like they are standing still, but they are actually very slow-moving rivers of ice. They move because of gravity. There are two main ways they move:
A. Basal Sliding (For "Warm-based" Glaciers)
In slightly warmer climates (like the Alps), the bottom of the glacier is just at the melting point. A thin layer of meltwater forms at the base. This water acts like a lubricant, allowing the glacier to slide over the rock below.
- Slippage: The ice slides over the meltwater.
- Creep: When the ice hits a bump, the pressure increases, making the ice act like a liquid to flow around the obstacle.
B. Internal Deformation (For "Cold-based" Glaciers)
In very cold places (like Antarctica), the ice is frozen solid to the rock. It can't slide. Instead, the ice crystals inside the glacier shift and slide over each other like a deck of cards being pushed. This is a much slower process.
Factors affecting speed:
- Gradient: Steeper slopes = faster movement.
- Ice Thickness: Thicker ice = more weight/pressure = faster movement.
- Temperature: Warmer ice moves more easily than freezing cold ice.
Common Mistake: Don't assume glaciers move at the same speed throughout. The middle and the surface move fastest because there is less friction with the valley sides and floor!
4. Periglacial Processes
The word periglacial literally means "around the glacier." These are cold environments that aren't covered by ice but are subject to intense freezing and thawing. The ground here is often permafrost (permanently frozen ground).
Key Periglacial Processes:
1. Freeze-Thaw Weathering
Water gets into cracks in rocks. When it freezes, it expands by about \(9\%\). This puts pressure on the rock. When it thaws, the pressure is released. Repeating this over and over breaks the rock apart into jagged pieces called scree.
2. Frost Heave
Water under stones in the soil freezes and expands, pushing the stones upward toward the surface. This creates "patterned ground" (like stone circles) often seen in tundra landscapes.
3. Solifluction
In the summer, the very top layer of the permafrost melts (this is called the active layer). Because the ground underneath is still frozen solid, the water can't soak in. The top layer becomes a "soupy" mess of mud and rocks that slowly slides downhill, even on very gentle slopes.
4. Nivation
This is a combination of processes (freeze-thaw, solifluction, and meltwater) that happens under a patch of snow. It hollows out the ground, creating a small depression that might eventually grow into a large cirque (or corrie) if a glacier forms.
Key Takeaways for Revision
1. Glaciers are systems: They have inputs (snow), stores (ice), and outputs (meltwater).
2. Mass Balance is a budget: If you "save" more ice than you "spend," the glacier grows.
3. Movement depends on water: Basal sliding is fast (lubricated by water); internal deformation is slow (ice crystals shifting).
4. Periglacial zones are "almost-glacial": They are dominated by freeze-thaw and the melting of the "active layer" (solifluction).
Next steps: Now that you know how the system moves, you're ready to look at the landforms these processes create, such as U-shaped valleys and moraines! (See chapter: 2A Glacial erosional, depositional and meltwater landforms).