Periglacial Processes and Landforms

Periglacial environments are areas that experience intense frost action and permafrost-related processes but are not covered by glacial ice. AQA A-Level Geography requires a detailed understanding of periglacial processes, the landforms they produce, and their vulnerability to climate change.

---

Defining Periglacial Environments

The term "periglacial" literally means "around the glacier" (from Greek peri = around), but the concept has expanded to include any cold, non-glacial environment where frost-related processes dominate.

Characteristics

• Mean annual temperature below 0°C (though some definitions extend to areas where the coldest month averages below −3°C)
• Freeze-thaw cycles are frequent and intense
• Permafrost may or may not be present
• Low precipitation — many periglacial areas are effectively cold deserts
• Sparse vegetation — tundra biome dominates

Global Distribution

Periglacial environments currently cover approximately 25% of the Earth's land surface, including:

• Arctic regions: Northern Canada, Alaska, Siberia, Scandinavia
• Antarctic margins: Areas beyond the ice sheet
• High-altitude regions: Alps, Himalayas, Rockies, Andes (above the tree line)
• Past periglacial environments: During the Pleistocene, much of southern England experienced periglacial conditions

---

Permafrost

Permafrost is ground that remains at or below 0°C for at least two consecutive years. It is the defining feature of most periglacial environments.

Types of Permafrost

Type	Characteristics	Distribution	Depth
Continuous	Permafrost underlies > 90% of the area	Highest latitudes (e.g., northern Siberia, Canadian Arctic islands)	Up to 1,500 m (in Siberia)
Discontinuous	Permafrost underlies 50–90% of the area	Slightly lower latitudes; absent under lakes, rivers and warm areas	25–100 m
Sporadic	Permafrost underlies 10–50% of the area	Lower latitudes; only in sheltered, north-facing slopes and shaded areas	10–25 m
Isolated patches	Permafrost underlies < 10% of the area	Margins of the periglacial zone; high-altitude locations	< 10 m

The Active Layer

The active layer is the surface layer of ground above the permafrost that thaws each summer and refreezes each winter.

• Depth: typically 0.3 m to 4 m, depending on latitude, altitude, soil type and vegetation cover
• Significance: All periglacial geomorphological processes operate within or because of the active layer
• The active layer is saturated in summer because meltwater cannot drain through the impermeable permafrost below — this waterlogging drives many periglacial processes

The Talik

A talik is an area of unfrozen ground within a permafrost region. Taliks can exist:

• Beneath lakes and rivers (where the water prevents freezing)
• Beneath buildings and infrastructure (where heat prevents freezing)
• Between the base of the active layer and the top of deep permafrost (in discontinuous zones)

---

Periglacial Processes

1. Frost Heave

Frost heave is the upward displacement of the ground surface caused by the formation of ice lenses within the soil.

Process:

1. As the active layer freezes from the surface downward, water migrates through the soil towards the freezing front by capillary action
2. The water freezes to form an ice lens — a horizontal layer of pure ice within the soil
3. As the ice lens grows, it pushes the soil above it upward
4. Multiple ice lenses can form at different depths, creating significant heaving of the ground surface
5. Upon thawing, the ground subsides unevenly, creating an irregular surface

Effects:

• Lifts stones to the surface (frost sorting)
• Disrupts roads, buildings and pipelines
• Contributes to the formation of patterned ground

2. Frost Sorting

Frost sorting is the process by which repeated freeze-thaw cycles separate coarse and fine particles in the soil.

Mechanism:

1. Frost heave preferentially lifts larger particles because they conduct heat more efficiently and freeze first
2. Coarse particles migrate to the surface and move outward
3. Fine particles remain in the centre
4. The result is a sorting of particles by size

3. Frost Shattering (Freeze-Thaw Weathering)

• Water enters cracks and joints in rock
• Upon freezing, water expands by approximately 9%, exerting pressures of up to 2,100 kN/m²
• Repeated freeze-thaw cycles shatter the rock into angular fragments
• Most effective where temperatures oscillate around 0°C
• Produces blockfields (felsenmeer), scree slopes and tors

4. Solifluction

Solifluction is the slow, downslope flow of waterlogged soil over an impermeable surface (usually permafrost).

Process:

1. In summer, the active layer thaws and becomes saturated (meltwater cannot drain through the permafrost below)
2. The waterlogged soil loses internal strength and begins to flow downslope under gravity
3. Rates of movement: typically 0.5 to 5 cm per year, but can exceed 50 cm per year on steep slopes
4. Creates distinctive solifluction lobes and solifluction terraces — tongue-shaped or terrace-shaped features on hillsides

Evidence in Southern England:

• Head deposits (also called coombe rock in chalk areas) found on many slopes in southern England are periglacial solifluction deposits from the Pleistocene
• These poorly sorted, angular deposits provide evidence that southern England experienced periglacial conditions during glacial periods

5. Nivation

• A combination of freeze-thaw weathering and solifluction operating around and beneath a snowpatch
• The snowpatch provides moisture for freeze-thaw and insulates the ground, creating a microclimate
• Gradually enlarges a hollow (nivation hollow) which may eventually develop into a corrie if snow accumulates sufficiently

---

Periglacial Landforms

Ice Wedges

Ice wedges are vertical, wedge-shaped bodies of ice that form in the ground through repeated thermal contraction and infilling.