Periglacial Processes and Landforms

Periglacial environments are areas that experience intense frost action and permafrost-related processes but are not covered by glacial ice. They currently occupy approximately 25% of the Earth's land surface and create a suite of distinctive landforms. Understanding periglacial processes is essential for Edexcel A-Level Geography Enquiry Question 1 (EQ1) and provides important context for synoptic links to climate change and the carbon cycle.

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Defining Periglacial Environments

The term "periglacial" literally means "around the ice" (from the Greek peri = around), originally referring to areas adjacent to ice sheets. Today, it is used more broadly to describe environments where frost-related processes dominate landscape development, regardless of proximity to glaciers.

Key Characteristics

Characteristic	Description
Temperature	Mean annual temperature below 0°C; frequent freeze-thaw cycles
Permafrost	Often present (though not universal in all periglacial areas)
Precipitation	Generally low (many periglacial areas are technically "cold deserts")
Vegetation	Sparse — tundra, mosses, lichens, sedges; treeline is a key boundary
Geomorphic processes	Frost action, permafrost-related processes, solifluction, nivation
Current distribution	Arctic and subarctic regions, high-altitude mountain areas, Antarctic fringes

Current Periglacial Regions

• Arctic tundra: Northern Russia (Siberia), northern Canada, Alaska, northern Scandinavia
• Antarctic fringe: Dry valleys and coastal areas of Antarctica
• High-altitude zones: Tibetan Plateau, Andes (above the treeline), high Alps, Himalayas
• Svalbard: The Norwegian archipelago at 74–81°N — a key study location for periglacial processes

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Permafrost

Permafrost is ground (soil, rock, sediment) that remains at or below 0°C for at least two consecutive years. It is defined by temperature, not by the presence of ice — permafrost may be "dry" (containing little or no ice) in some locations.

Types of Permafrost

Type	Distribution	Mean Annual Temperature	Depth	Characteristics
Continuous	Widespread in the High Arctic (> 90% of ground)	Below −5°C to −10°C	200–1,500+ m (up to 1,500 m in Siberia)	Permanent, deep, few unfrozen zones (taliks)
Discontinuous	Intermediate latitudes (50–90% of ground)	−1°C to −5°C	10–100 m	Interrupted by unfrozen areas under lakes, rivers and south-facing slopes
Sporadic	Southern margins of permafrost zone (< 50% of ground)	0°C to −1°C	< 10 m	Patchy; found only in sheltered locations (north-facing slopes, peat bogs)
Relict	Present in formerly periglacial areas	Currently above 0°C	Variable	Remnants of past permafrost; found at depth in parts of northern England

The Active Layer

The active layer is the surface layer of ground above the permafrost that thaws in summer and refreezes in winter. Its depth varies:

Location	Active Layer Depth	Controlling Factors
High Arctic	0.3–0.5 m	Very low summer temperatures; short thaw season
Subarctic	1–3 m	Warmer summers; longer thaw season
Alpine	1–5 m	Strong solar radiation; thin or absent vegetation

The active layer is where most periglacial geomorphic processes occur. It is a zone of intense seasonal activity — freezing and thawing cause expansion and contraction of the ground, movement of water and disruption of sediments.

graph TD
    A["Ground Surface"] --> B["ACTIVE LAYER<br/>Thaws in summer<br/>Refreezes in winter<br/>Depth: 0.3–5 m"]
    B --> C["PERMAFROST TABLE<br/>(boundary between active<br/>layer and permafrost)"]
    C --> D["PERMAFROST<br/>Permanently frozen<br/>ground (≥ 2 years)<br/>Depth: up to 1,500 m"]
    D --> E["BASE OF PERMAFROST<br/>(geothermal heat<br/>warms ground above 0°C)"]
    E --> F["UNFROZEN GROUND<br/>(below permafrost)"]

Exam Tip: Always distinguish between the active layer (seasonal freezing and thawing) and permafrost (permanently frozen). Many periglacial processes operate specifically within the active layer, not within the permafrost itself. Getting this distinction right demonstrates precise understanding.

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Periglacial Processes

Frost Heave

Frost heave is the upward expansion of the ground surface caused by the formation of ice lenses in the soil:

1. Water migrates upward through soil capillaries toward the freezing front (the boundary between frozen and unfrozen ground)
2. As this water freezes, it forms horizontal layers of pure ice called ice lenses
3. The ice lenses grow by drawing more water upward, expanding the ground upward
4. The result is a net upward displacement of the ground surface, which can be 10–30 cm per winter in active periglacial areas

Frost heave sorts sediments by pushing coarser particles upward and outward (stones rise through the soil faster than fine-grained material). This process contributes to the formation of patterned ground.

Frost Contraction and Ice Wedges

In continuous permafrost regions, extreme winter cold causes the frozen ground to contract and crack — a process analogous to mud cracking as it dries:

1. In winter, when temperatures drop below approximately −15°C to −20°C, the ground contracts and thermal contraction cracks form (typically 2–3 cm wide)
2. In spring, meltwater seeps into the cracks and freezes
3. The following winter, the ground contracts again, but the ice in the crack prevents full closure — the crack reopens and may widen
4. Over centuries to millennia, repeated cycles build ice wedges — vertical, wedge-shaped masses of ice up to 1–2 m wide at the top and 3–10 m deep
5. The ice wedges form polygonal networks visible from the air — ice-wedge polygons (typically 10–30 m across)

Solifluction

Solifluction is the slow, downslope flow of waterlogged soil over an impermeable layer — in periglacial environments, the impermeable layer is the permafrost table.

• In summer, the active layer thaws and becomes saturated (water cannot drain through the underlying frozen permafrost)
• The waterlogged soil flows slowly downhill under gravity, even on very gentle slopes (as low as 1–2°)
• Rates of movement: typically 1–10 cm per year, though up to 30 cm/year on steeper slopes
• Creates distinctive solifluction lobes and solifluction terraces — tongue-shaped masses of soil that move downslope, often with a bulging front edge