Welcome to Glacial Systems and Processes!
Hi there! Welcome to your study notes for the "Systems and Processes" part of the Glacial Landscapes chapter. Don't worry if the word "system" sounds a bit like computer science—in Geography, it’s just a way of looking at how different parts of nature work together. By the end of these notes, you’ll understand how glaciers grow, move, and shape the world like giant, icy conveyor belts. Let’s get started!
3.1.3.1 Glaciers as Natural Systems
Think of a glacier like a bank account. You have money coming in (snow) and money going out (melting). The "balance" in the account determines if the glacier grows or shrinks.
1. Inputs (Money In): These are things that add mass to the glacier. The main input is accumulation (mostly snowfall and avalanches from mountainsides).
2. Outputs (Money Out): These are things that take mass away, known as ablation. This includes melting, sublimation (ice turning straight into gas), and calving (chunks of ice breaking off into the sea).
3. Stores: This is the glacier itself—the ice and the debris (rocks) it carries.
4. Flows/Transfers: This is the movement of the ice downslope due to gravity.
5. Energy: Glaciers get their energy from gravity (pulling them down) and solar radiation (causing melting).
Feedback Loops: Nature’s Way of Reacting
Sometimes a change in the system causes a "loop" of reactions:
• Negative Feedback: This is like a thermostat. It keeps things stable. Example: If a glacier grows too big, it might move into a warmer area where it melts faster, bringing it back to its original size. This state of balance is called dynamic equilibrium.
• Positive Feedback: This makes a change even bigger. Example: As a glacier melts, it reveals darker ground underneath. Darker ground absorbs more heat than white snow, making the glacier melt even faster!
Quick Review:
• Input = Accumulation (Snow)
• Output = Ablation (Melting)
• System = The whole "glacier machine" working together.
3.1.3.3 Systems and Processes: The Glacial Budget
The glacial budget (or mass balance) is the difference between total accumulation and total ablation over one year.
We can write it as a simple equation:
\( Net Balance = Accumulation - Ablation \)
• If accumulation is higher than ablation, the glacier has a positive budget and will advance (get longer).
• If ablation is higher, it has a negative budget and will retreat (look like it's shrinking back up the mountain).
• The equilibrium line is the "sweet spot" on the glacier where accumulation exactly equals ablation.
Warm-Based vs. Cold-Based Glaciers
Not all glaciers are the same temperature! This matters because it changes how they move.
• Warm-based (Temperate) Glaciers: These are found in mountain areas like the Alps. The ice is at or near the melting point. Because there is liquid meltwater at the bottom, they act like they are on a "slip-and-slide" and move very quickly.
• Cold-based (Polar) Glaciers: These are found in places like Antarctica. The ice is well below freezing. They are frozen to the rock beneath them and move incredibly slowly—almost like very stiff honey.
How Glaciers Move
Moving a massive block of ice isn't easy! Glaciers use several methods:
1. Basal Sliding: Common in warm-based glaciers. Meltwater at the base acts as a lubricant, letting the glacier slide over the rock.
2. Internal Deformation: Imagine a deck of cards. If you push the top, the cards slide over each other. Ice crystals do the same thing under the weight of the glacier.
3. Extensional Flow: When the glacier goes down a steep slope, it speeds up and the ice stretches and cracks (forming crevasses).
4. Compressional Flow: When the slope levels out, the ice slows down and "bunches up," getting thicker.
5. Rotational Flow: This happens in hollows on a mountainside. The ice moves in a curved, circular motion, which helps carve out deep bowls.
Memory Aid: Think of "Internal Deformation" as "Icy Sliding" inside the glacier itself!
Geomorphological Processes: Shaping the Land
Geomorphological just means "land-shaping." Glaciers are like giant pieces of sandpaper—they don't just sit there; they tear up the landscape.
1. Weathering
Weathering happens to the rock around the glacier:
• Frost Action (Freeze-Thaw): Water gets into cracks in rocks, freezes, expands, and snaps the rock apart. This provides the "tools" (shattered rock) for the glacier to erode with.
• Nivation: This is a "pre-glacial" process where snow sits in a small hollow. Through freeze-thaw and melting, it slowly deepens that hollow into a bowl shape.
2. Erosion: The Sandpaper and the Crowbar
Glaciers erode in two main ways:
• Plucking (The Crowbar): Meltwater freezes onto the rock at the base. As the glacier moves, it "plucks" whole chunks of rock out of the ground.
• Abrasion (The Sandpaper): The rocks stuck in the bottom of the glacier rub against the bedrock as the ice moves, scraping it away. This leaves behind scratches called striations.
3. Transportation and Deposition
Glaciers carry anything from tiny dust to house-sized boulders. This material is called moraine. When the glacier loses energy or melts, it drops this load. Unlike a river, which sorts rocks by size, a glacier just drops everything in a big, messy pile called till.
Key Takeaway: Erosion is the "taking away," Transportation is the "carrying," and Deposition is the "dropping off."
Fluvioglacial and Periglacial Processes
Glacial environments aren't just about ice; they are also about water and frozen ground.
Fluvioglacial Processes (Meltwater)
When glaciers melt, they create huge amounts of meltwater. This water can erode and move sediment just like a river, but it’s often under high pressure under the ice. These processes are called fluvioglacial (fluvio = river, glacial = ice).
Periglacial Processes (Near the Ice)
Periglacial areas are "at the edge" of glaciers. It's cold, but not covered in ice year-round.
• Permafrost: Ground that stays frozen for two or more years.
• Active Layer: The top layer of soil that thaws in the summer and freezes in the winter. Because the water can't drain through the frozen ground below, this layer becomes a "soupy" mess.
• Mass Movement (Solifluction): This is like a very slow "mudslide" of the active layer. Because the ground is so soggy, it slowly creeps downslope due to gravity.
Quick Review Box: Common Mistakes to Avoid
• Mistake: Thinking glaciers "retreat" by physically turning around and moving uphill.
• Reality: The front of the glacier just melts faster than the ice is moving forward. It’s like a conveyor belt where the end is melting off faster than the belt is moving.
• Mistake: Thinking glaciers only erode by melting.
• Reality: Most erosion is mechanical (plucking and abrasion).
Final Summary of Systems and Processes
Glaciers are open systems driven by the balance of snow in and meltwater out. They move through sliding and internal stretching, and they shape the land through the powerful "one-two punch" of plucking and abrasion. Around the edges, periglacial processes like freeze-thaw and solifluction continue to shift the landscape. Understanding these processes is the key to explaining all those cool landforms you'll study in the next section!