Welcome to the World of Periglacial Landscapes!

When we think of ice-cold environments, we usually imagine massive glaciers or ice sheets. But there is a whole other world sitting right on the edge of these icy giants. These are periglacial landscapes. The word literally means "around the ice" (peri = around, glacial = ice). These environments are unique because the ground is permanently frozen, but the top layer thaws out every summer, creating some of the most unusual and "alien-looking" landscapes on Earth.

In this chapter, we will explore how freezing and thawing shape the land and learn about the distinctive features that appear in these chilly regions.

1. What is Permafrost?

The defining feature of a periglacial landscape is permafrost. Permafrost is ground (soil or rock, including ice or organic material) that remains at or below \(0^\circ C\) for at least two consecutive years.

Think of permafrost like a "frozen sandwich":

  • The Active Layer: This is the top layer of soil. It thaws during the brief summer and refreezes in the winter. Because the water cannot drain through the frozen ground below, this layer becomes very soggy and "mushy" in the summer.
  • The Permafrost: This is the permanently frozen ground below the active layer. It acts like a solid, waterproof floor.
  • Talik: This is any patch of unfrozen ground found within or below the permafrost.

Quick Tip: Don't worry if you find the types of permafrost confusing! Just remember that continuous permafrost covers everything in the coldest areas, while discontinuous permafrost occurs in slightly warmer areas where some patches of ground stay unfrozen.

2. The Engine of Change: Periglacial Processes

How does a flat field turn into a landscape of strange mounds and stone circles? It’s all down to a few key processes driven by the freezing and thawing of water.

A. Freeze-Thaw Weathering

This is the "classic" process. Water enters cracks in rocks. When it freezes, it expands by approximately \(9\%\) in volume. This puts immense pressure on the rock. When it thaws, the pressure is released. Repeated over and over, this physical weathering eventually shatters the rock into sharp, angular fragments.

B. Frost Heave

Imagine stones being "pushed" out of the ground from below. As the ground freezes, ice lenses (small pockets of ice) form in the soil. These ice lenses expand and lift the soil and stones upward. Because smaller particles (silt/sand) settle back down faster than large stones during the thaw, the stones eventually end up sitting on the surface.

C. Solifluction (The "Soggy Slide")

In the summer, the active layer thaws. Because the water cannot drain away through the frozen permafrost below, the soil becomes saturated and heavy. Even on very gentle slopes, this "soupy" soil begins to slide slowly downhill. This process is called solifluction (which literally means "soil flow").

D. Nivation

This is a "multi-tasking" process that happens under snow patches. It involves freeze-thaw weathering, chemical weathering, and the removal of debris by meltwater. Over time, nivation carves out small hollows in the hillside, which can eventually grow into larger features like cirques (which you will learn about in the glacial landforms chapter).

Key Takeaway: Periglacial landscapes are shaped by the active layer freezing and thawing. Without this seasonal "on-off" switch for ice, these landforms wouldn't exist!

3. Distinctive Periglacial Landforms

These processes create specific features that geographers look for to identify periglacial environments.

Pingos: The Ice Mounds

A pingo is a large, ice-cored mound that can grow up to \(50\) metres high. There are two main types:

  • Open-system pingos: Found in valley bottoms. Water is forced up through the gaps in the discontinuous permafrost under hydraulic pressure, freezes, and lifts the ground above it.
  • Closed-system pingos: These form under lake beds. When a lake fills with sediment or drains, the saturated ground below freezes. The permafrost grows inward, trapping a "pocket" of water (talik). As this water freezes, it expands and pushes the ground up into a dome.

Patterned Ground

If you looked down from a helicopter, you might see the ground arranged in perfect circles, polygons, or stripes of stones. This is patterned ground. It is caused by frost heave. As stones are pushed to the surface, they roll or slide to the edges of small mounds, naturally sorting themselves into geometric shapes. On steeper slopes, these circles get stretched by gravity into stone stripes.

Blockfields (Felsenmeer)

In areas where freeze-thaw weathering is very intense, the ground is covered in a chaotic "sea" of jagged rocks. These are called blockfields. They look like a giant has smashed a mountain with a hammer.

Solifluction Lobes and Terrasettes

When the active layer slides downhill (solifluction), it doesn't always move at the same speed. It forms tongue-shaped "lobes" of soil at the bottom of slopes. If the movement creates small, step-like features on a hillside, we call them terrasettes.

Did you know? Many of these features can be seen in the UK today (like on the tops of the Scottish Highlands or the Pennines), but they are relict features—this means they were formed during the last Ice Age and aren't "active" anymore because the climate has warmed up!

4. Summary and Common Pitfalls

Quick Review:
• Periglacial means "near-glacial" and is defined by permafrost.
• The active layer is the secret to everything; its seasonal melting allows movement and shaping.
• Frost heave creates patterned ground.
• Solifluction is the slow, downhill flow of saturated soil.
• Pingos are ice-cored mounds formed by water pressure and freezing.

Common Mistakes to Avoid:
1. Glacial vs. Periglacial: Remember, periglacial landscapes are not covered by glaciers. They are dominated by frozen ground, not moving rivers of ice.
2. Solifluction vs. Landslides: Solifluction is extremely slow (often only a few centimetres a year), whereas a landslide is a fast, catastrophic event.
3. Pingos are not volcanoes: They might look like small volcanoes, but there is no lava involved—only the power of expanding ice!

Key Specialist Concept: Systems
Think of the periglacial landscape as a system. The input is cold climate and moisture; the processes are freeze-thaw and frost heave; and the outputs are the distinctive landforms like pingos and patterned ground. If the climate warms up (an environmental change), the system changes, the permafrost melts, and the landforms become "relict" or disappear.