Welcome to Glaciated Landscapes and Change!
In this chapter, we are going to explore some of the most powerful and beautiful landscapes on Earth. Think of glaciers as nature’s giant bulldozers—they carve out massive valleys, move mountains of rock, and leave behind unique shapes that we can still see today, even in places where the ice melted thousands of years ago. Whether you find physical geography easy or a bit of a mountain to climb, these notes will help you reach the summit!
1. Climate Change and the "Big Freeze"
To understand glaciers, we first need to look at the Earth's "temperature diary." The climate hasn't stayed the same; it swings between cold glacials (ice ages) and warmer interglacials (like the one we are in now).
A Timeline of Change
- Pleistocene: This was the era of "The Great Ice Age." It began about 2.6 million years ago. During this time, huge ice sheets covered much of the UK.
- Holocene: This is our current era, which started about 11,700 years ago when the ice began to retreat.
- Anthropocene: A new term used to describe the most recent period where human activity has become the biggest influence on climate and the environment.
Why does the climate change?
Don't worry if this seems technical; just think of these as the Earth’s "thermostat" settings:
- Milankovitch Cycles: These are tiny changes in how the Earth orbits the sun. Sometimes we are slightly closer or tilted differently, which changes how much heat we get. Analogy: Imagine a spinning top—as it spins, it also wobbles and shifts its path. That's what the Earth does!
- Solar Output: The sun doesn't always shine with the same strength; it has cycles of high and low energy.
- Volcanic Eruptions: Massive eruptions can throw ash into the sky, blocking out sunlight and cooling the Earth.
- Atmospheric Gases: Changes in \(CO_2\) and methane trap heat.
Quick Review: The Earth cycles between cold and warm periods. We are currently in a warm period (Holocene) but are seeing rapid changes due to humans (Anthropocene).
2. The Cryosphere: Where is the ice?
The Cryosphere is simply the part of the Earth's surface where water is frozen. It's like a giant global refrigerator!
Types of Ice Masses
Glaciers come in different sizes, just like vehicles:
- Ice Sheets: The "jumbo jets." Massive continental-sized ice (e.g., Antarctica and Greenland).
- Ice Caps: Smaller than sheets, covering mountain ranges.
- Valley Glaciers: Like "long trucks" that flow down through mountain valleys.
- Cirque Glaciers: Small "mini-cars" that sit in bowl-shaped hollows on mountainsides.
Did you know?
During the Pleistocene, ice sheets reached as far south as London! We know this because of the "relict" (leftover) landscapes like the Lake District or the Scottish Highlands.
3. Periglacial Landscapes (The "Edge" of Ice)
Periglacial means "around the glacier." These are cold areas that aren't covered by ice but are frozen for most of the year. Think of the Tundra in Northern Canada or Russia.
Key Processes
- Permafrost: Ground that stays frozen for at least two years. It can be continuous (everywhere), discontinuous, or sporadic.
- Active Layer: The top layer of soil that thaws in the summer and freezes in the winter. It’s very mushy and unstable!
- Freeze-Thaw Weathering: Water gets into cracks in rocks, freezes, expands, and breaks the rock apart.
- Solifluction: In summer, the thawed active layer "slides" over the frozen permafrost below—like a slow-motion mudslide.
Unique Landforms
- Pingos: Huge ice-cored mounds that look like small hills.
- Patterned Ground: Stones arranged in circles or polygons caused by frost heave (ice pushing stones to the surface).
Takeaway: Periglacial areas are shaped by freezing and thawing ground, not by moving ice sheets.
4. Glaciers as a System (Mass Balance)
A glacier is like a bank account. You have "deposits" and "withdrawals."
The Formula
The "health" of a glacier is called its Mass Balance:
\(Net\ Balance = Accumulation - Ablation\)
- Accumulation: Snow falling and turning into ice (Depositing money).
- Ablation: Melting, evaporation, or "calving" (ice breaking off into the sea) (Spending money).
- Equilibrium Line: The "break-even" point where accumulation equals ablation.
Positive Balance: If there’s more snow than melting, the glacier advances (grows).
Negative Balance: If there’s more melting than snow, the glacier retreats (shrinks).
5. How do Glaciers Move?
Glaciers don't just sit there; they flow downhill because of gravity. But they move in different ways depending on how "warm" they are.
Two Main Types:
- Polar (Cold-based) Glaciers: These are frozen to the bedrock. They move very slowly by "internal deformation" (the ice crystals sliding over each other). Analogy: Like cold, stiff honey.
- Temperate (Warm-based) Glaciers: These have a layer of meltwater at the bottom. This acts as a lubricant, allowing the glacier to slide quickly. This is called basal slip. Analogy: Like an ice cube sliding across a kitchen counter on a film of water.
Common Mistake: Students often think glaciers move like liquid water. They don't! They move through a mix of sliding and internal shifting, and speed varies based on slope and ice thickness.
6. Carving the Land (Erosional Landforms)
Glaciers are the ultimate sculptors. They use two main "tools":
- Plucking: The glacier freezes onto rocks and "plucks" them out of the ground as it moves.
- Abrasion: Rocks stuck in the bottom of the ice act like sandpaper, grinding down the valley floor.
What do they leave behind?
- Cirques (Corries): Large, bowl-shaped hollows (e.g., Red Tarn in the Lake District).
- Arêtes: Sharp, "knife-edge" ridges between two cirques.
- Pyramidal Peaks: A pointed mountain peak created when three or more cirques erode back-to-back (e.g., The Matterhorn).
- U-Shaped Valleys (Glacial Troughs): Glaciers turn narrow V-shaped river valleys into wide, deep U-shaped ones.
- Ribbon Lakes: Long, thin lakes on the valley floor (e.g., Windermere).
Quick Trick: If the valley is wide and flat at the bottom, it's a Glacial Trough. If it's narrow and steep, it's a River Valley.
7. Dropping the Load (Depositional Landforms)
When a glacier melts, it drops everything it was carrying. This material is called Till (or "boulder clay"). It is unsorted, meaning big boulders and tiny clay are all mixed together.
Key Landforms:
- Moraines: Ridges of till. Lateral (at the sides), Terminal (at the very end), and Medial (in the middle).
- Drumlins: Smooth, egg-shaped hills. They show us which way the ice was moving! The "blunt" end points to where the ice came from.
- Erratics: Random, massive boulders dropped in a place where the local geology is completely different. Example: A piece of granite dropped on a limestone field.
8. Glacial Meltwater (Fluvioglacial Landforms)
As glaciers melt, they create massive rivers. These rivers carry sediment and create fluvioglacial landforms. Unlike glacial till, these deposits are sorted (heavy rocks drop first, light sand later).
Landforms to remember:
- Eskers: Long, winding ridges of sand and gravel. They are actually the "skeletons" of rivers that once flowed in tunnels inside the glacier!
- Kames: Small mounds of sorted sediment.
- Outwash Plains (Sandurs): Large, flat areas of sand and gravel in front of the glacier.
- Kettle Holes: Small lakes formed when a block of ice gets buried in sediment, melts, and leaves a hole.
Summary: Glacial deposits = messy and unsorted. Fluvioglacial deposits = neat and sorted by water.
9. Managing Glaciated Landscapes Today
These landscapes are beautiful but fragile. We use them for many things, which can cause conflict.
Why do we value them?
- Economic: Tourism (skiing, hiking), Hydroelectric Power (HEP) from meltwater, and mining.
- Environmental: They are unique habitats for biodiversity (Tundra).
- Cultural: Spiritual or religious importance for indigenous people.
The Threats
- Climate Change: This is the biggest threat. Glaciers are melting at record speeds (e.g., Himalayan Glaciers), which threatens water supplies for millions of people.
- Natural Hazards: Avalanches and GLOFs (Glacial Lake Outburst Floods)—when a natural dam of ice or rock breaks, sending a wall of water downstream.
- Human Pressure: Over-tourism can lead to soil erosion and pollution.
Management Strategies
Different people (stakeholders) want different things. Conservationists want to preserve the ice, while power companies want to use the water for electricity. Successful management requires global cooperation (like the Antarctic Treaty) and local planning to ensure these landscapes are around for future generations.
Final Thought: Glaciated landscapes are a "frozen history" of our planet. By studying them, we learn about our past and get a warning about our future climate!