Welcome to Glacial Systems!
Welcome to one of the most exciting parts of your AQA Geography course! Don't worry if the word "Systems" sounds a bit like a computer science lesson—in Geography, a system is just a way of looking at how different parts of nature work together. Think of a glacier like a giant ice machine: it takes in "fuel" (snow), processes it, and eventually "spits out" waste (meltwater and rocks). In these notes, we’ll break down exactly how this machine works.
Geography Tip: Glaciers are more than just ice; they are dynamic, moving forces that shape our planet!
1. The Glacial System: Inputs, Outputs, and Stores
To understand a glacier, imagine a bank account. You have money coming in (snow), money staying in the account (ice), and money being spent (melting). If you save more than you spend, the account grows!
Key Components:
Inputs: These are things added to the system. The main input is accumulation (mostly snowfall). Other inputs include avalanches from valley sides and debris (rocks) falling onto the ice.
Outputs: Also known as ablation. This is the loss of ice. It happens through melting, evaporation, and calving (when chunks of ice break off into the sea to form icebergs).
Stores: The glacier itself! This is where the ice is kept for hundreds or thousands of years.
Transfers (Flows): This is the movement of ice from the top of the mountain (accumulation zone) down to the bottom (ablation zone) due to gravity.
The Concepts of Equilibrium
Dynamic Equilibrium: This happens when the inputs and outputs are equal. The glacier stays the same size. It’s a "moving balance."
Negative Feedback: This is the system’s way of fixing itself. If a glacier grows too big, it might flow faster into warmer air at lower altitudes, causing it to melt more quickly and return to its original size.
Positive Feedback: This makes a change even bigger. Example: The Albedo Effect. If ice melts, there is less white surface to reflect sunlight. The dark ground absorbs more heat, making it even warmer, which melts even more ice!
Quick Review:
- Accumulation = Snow coming in.
- Ablation = Ice going out.
- Mass Balance = The difference between the two.
2. Glacial Budgets: The Math of Ice
Glaciologists use a "budget" to see if a glacier is growing or shrinking. This is called the Glacial Budget or Mass Balance.
The simple formula is:
\( Net\ Balance = Accumulation - Ablation \)
The Two Zones:
1. The Accumulation Zone: High up on the mountain where it’s cold. Here, more snow falls than melts. The budget is positive.
2. The Ablation Zone: Lower down where it’s warmer. Here, more ice melts than falls as snow. The budget is negative.
The line between these two areas is the Equilibrium Line (or snow line). If this line moves up the mountain, the glacier is retreating (shrinking)!
Memory Aid: ABC
Accumulation = Budget increases.
Calving/Ablation = Budget decreases.
3. Warm-based vs. Cold-based Glaciers
Don't worry if this seems tricky! The main difference is simply temperature and how it affects movement.
Warm-based (Temperate) Glaciers
Found in places like the Alps or Rockies. The temperature of the ice is right at the Pressure Melting Point (PMP). This means the ice is just warm enough to melt slightly under pressure.
Result: There is a layer of meltwater at the bottom. This acts like lubricant, allowing the glacier to slide quickly (up to 300m per year!). These glaciers do a lot of erosion.
Cold-based (Polar) Glaciers
Found in Antarctica or Greenland. The temperature is way below freezing. Even the bottom of the glacier is frozen solid to the bedrock.
Result: No meltwater at the bottom. The glacier is "stuck." It moves very slowly (maybe only a few meters a year) only through internal shifting of ice crystals. These glaciers do very little erosion.
Analogy:
Warm-based: Like sliding down a wet water slide (fast and smooth).
Cold-based: Like being stuck to a dry slide while wearing velcro (hardly moving at all).
4. Geomorphological Processes: How Glaciers Change the Land
Glaciers are like giant sheets of sandpaper. They don't just sit there; they actively shape the mountains.
A. Weathering (Breaking down rocks)
Frost Action (Freeze-Thaw): Water gets into cracks in the rock. At night, it freezes and expands (by 9%!). This pushes the crack open. During the day, it melts. Repeat this many times, and the rock shatters into scree.
Nivation: This is "snow-patch erosion." Snow sits in a hollow. Freeze-thaw weathering and meltwater wash away the broken rock, making the hollow deeper and wider over time. This is the first step in forming a corrie!
B. Erosion (Carving the land)
Plucking: As the glacier moves, meltwater at the bottom freezes onto the rocks behind it. As the glacier pulls away, it literally plucks huge chunks of rock out of the ground.
Abrasion: The rocks stuck in the bottom of the glacier (from plucking) act like sandpaper. They grind away at the bedrock as the ice moves, leaving it smooth with scratches called striations.
C. Transportation and Deposition
Glaciers carry anything from tiny sand grains to house-sized boulders. This material is called Moraine.
- Supraglacial: Carried on top of the ice.
- Englacial: Carried inside the ice.
- Subglacial: Dragged along the bottom.
When the glacier loses energy (melts), it drops everything. Unlike a river, a glacier drops everything at once, meaning glacial deposits (called Till) are unsorted—big rocks and tiny clay all mixed together.
5. Ice Movement: How Glaciers Flow
Glaciers move because of gravity. But they move in different ways depending on the slope and temperature.
Basal Sliding
Only in warm-based glaciers. The meltwater at the base reduces friction. Enhanced basal creep happens when the ice meets a small bump; the pressure causes it to melt, flow around the bump, and refreeze on the other side.
Internal Deformation
In cold-based glaciers. Ice crystals slide over each other like a deck of cards. This is how the ice moves when it’s too cold to slide.
Extensional and Compressional Flow
Extensional Flow: When the glacier goes down a steep slope, it speeds up. The ice thins and pulls apart, creating deep cracks called crevasses.
Compressional Flow: When the slope becomes gentle, the ice slows down and "bunches up." The ice gets thicker.
Did you know?
A Glacial Surge is when a glacier suddenly moves up to 100 times faster than normal! This is usually caused by a sudden build-up of meltwater at the base.
Summary Takeaways
1. Glaciers are systems: Inputs (snow) and Outputs (melt) determine if they grow or shrink.
2. Temperature is key: Warm-based glaciers slide on meltwater; cold-based glaciers are frozen to the ground.
3. Erosion is a team effort: Plucking pulls rocks out, and Abrasion uses those rocks to grind the valley down.
4. Movement: Gravity pulls ice down, either by sliding at the bottom or shifting crystals inside.
Don't worry if you find the movement types confusing at first. Just remember: Warm = Sliding; Cold = Internal shifting!