Welcome to Glacial Systems!
Hello! Today we are looking at glaciers as natural systems. Don’t worry if this seems a bit "scientific" at first. Think of a glacier not just as a big block of ice, but as a living machine or even a bank account. It takes things in, moves them around, and spits things out. By the end of these notes, you’ll understand how glaciers stay in balance and why they are such powerful sculptors of our landscape.
Note: These notes focus specifically on the "system" part of the AQA 7037 syllabus (sections 3.1.4.1 to 3.1.4.3).
1. Glaciers as Open Systems
In Geography, an open system is something that has things entering it (inputs) and things leaving it (outputs). Because energy and matter (ice/snow) cross the "boundary" of the glacier, it is an open system.
The Parts of the System:
Inputs: These are things added to the glacier. The main one is precipitation (snow, rain, and avalanches from mountainsides). Solar energy is also an input that drives melting.
Outputs: These are things leaving the glacier. This includes meltwater, calving (chunks of ice breaking off into the sea to form icebergs), and sublimation (ice turning directly into gas).
Stores: This is the ice itself. A glacier is essentially a massive store of frozen freshwater.
Flows (Transfers): This is the movement of the ice. Gravity pulls the heavy ice downhill, moving it from the top of the mountain to the valley below.
Quick Review: The Bathtub Analogy
Imagine a bathtub. The tap is the input (snow). The water in the tub is the store (ice). The drain is the output (melting). If the tap is faster than the drain, the water level rises (the glacier grows!).
2. The Glacial Budget (Mass Balance)
The glacial budget is just a way of seeing if the glacier is "saving" ice or "spending" it. It is the difference between accumulation (gaining ice) and ablation (losing ice) over a year.
The formula for Net Balance is:
\( \text{Net Balance} = \text{Accumulation} - \text{Ablation} \)
Two Important Zones:
1. The Zone of Accumulation: Usually at the top of the glacier (where it’s colder). Here, more snow falls than melts. The budget is positive.
2. The Zone of Ablation: Usually at the bottom (the "snout"). Here, more ice melts than is replaced by snow. The budget is negative.
3. The Equilibrium Line: This is the "sweet spot" in the middle where accumulation and ablation are exactly equal. It’s like having exactly enough money in your bank account to pay your bills—no more, no less.
What happens when the budget changes?
- If Accumulation > Ablation: The glacier has a positive budget and the snout advances (moves down the valley).
- If Ablation > Accumulation: The glacier has a negative budget and the snout retreats (appears to move back up the valley).
Common Mistake to Avoid: Even when a glacier is "retreating," the ice is still flowing forward due to gravity. It’s just melting at the bottom faster than it can be replaced. Think of it like a treadmill: you are running forward, but the belt is moving you backward faster than you can run!
3. Types of Glaciers: Warm vs. Cold Based
Not all glaciers move in the same way. Temperature is the "engine" that decides how they behave.
Warm-based (Alpine) Glaciers:
These are found in places like the Alps or the Rockies. The temperature is often near the Pressure Melting Point (PMP).
Did you know? Pressure makes ice melt at lower temperatures. Because these glaciers are heavy, the ice at the bottom can melt even if it's 0°C. This creates meltwater at the base, which acts like grease on a slide, making the glacier move fast (sometimes 20-30 meters a year!).
Cold-based (Polar) Glaciers:
These are found in Antarctica or Greenland. The air is so cold that the ice stays well below freezing, even at the bottom. These glaciers are frozen to the bedrock. Because there is no "grease" (meltwater), they move very, very slowly—mostly only a few centimeters a year.
Key Takeaway: Meltwater is the key to movement. No water = slow movement. Plenty of water = fast movement.
4. How Glaciers Move (The Mechanics)
Don't worry if this seems tricky! Just remember that ice is "plastic"—it can bend and stretch before it breaks.
1. Basal Sliding: Only in warm-based glaciers. The ice slides over the rock on a thin layer of meltwater.
2. Internal Deformation: The weight of the ice causes ice crystals to slide over each other (like a deck of cards being pushed).
3. Extensional Flow: When the glacier goes over a steep drop, the ice speeds up and stretches. This creates deep cracks called crevasses.
4. Compressional Flow: When the gradient flattens out, the ice slows down and "bunches up," becoming thicker.
5. Rotational Flow: This happens in "corries" (armchair-shaped hollows). The ice moves in a curved, circular motion, which carves out deep holes in the mountain.
Memory Aid: "B.I.C.E."
B - Basal Sliding
I - Internal Deformation
C - Compressional Flow
E - Extensional Flow
5. Geomorphological Processes
Glaciers are "landform factories." They use three main processes:
Weathering (Frost Action): Water gets into cracks in the rock, freezes, expands, and breaks the rock apart. This is also called freeze-thaw.
Erosion:
- Plucking: Meltwater freezes onto rocks and "plucks" them out of the ground as the glacier moves.
- Abrasion: The rocks stuck in the bottom of the glacier act like sandpaper, grinding down the valley floor.
Nivation: A "pre-glacial" process where snow sits in a hollow. Freeze-thaw and meltwater erosion happen underneath the snow patch, deepening the hollow before a glacier even forms.
Quick Review Box:
- System: Inputs (Snow), Stores (Ice), Outputs (Melting).
- Mass Balance: Accumulation vs. Ablation.
- Warm-based: Fast, sliding on water.
- Cold-based: Slow, frozen to rock.
- Erosion: Plucking (pulling) and Abrasion (sanding).