Periglacial Environments

Periglacial environments are areas that experience cold temperatures and freeze-thaw processes but are not covered by glacial ice. The term was coined by the Polish geomorphologist Walery Łoziński (1909) to describe the conditions found around the margins of glaciers and ice sheets. Today, periglacial processes operate across approximately 25% of the Earth's land surface — a far greater area than is actually glaciated.

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Distribution of Periglacial Environments

Periglacial conditions are found in:

• High-latitude regions — Arctic Canada, Siberia, Alaska, northern Scandinavia, Antarctica
• High-altitude regions — Alpine environments, the Tibetan Plateau, the Andes
• Mid-latitude areas during cold periods — much of lowland Britain experienced periglacial conditions during Pleistocene cold stages when ice sheets did not extend that far south

Key Definition: A periglacial environment is one where the mean annual temperature is below 0°C for at least part of the year, and freeze-thaw processes are the dominant geomorphological agents, but the area is not permanently covered by glacier ice.

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Permafrost

Permafrost is ground that remains at or below 0°C for at least two consecutive years. It is the defining characteristic of periglacial environments. The depth and distribution of permafrost vary with climate:

Types of Permafrost

Type	Mean Annual Temperature	Coverage	Depth	Location Examples
Continuous	Below −5°C to −10°C	>90% of ground surface	Up to 1,500 m in Siberia	Central Siberia, northern Alaska, Canadian Arctic Archipelago
Discontinuous	−1°C to −5°C	50–90% of surface	Typically 10–100 m	Southern Alaska, northern Canada (boreal zone), parts of Scandinavia
Sporadic	0°C to −1°C	<50% of surface	A few metres	Southern margins of permafrost zone; mountain areas at lower latitudes

Key Fact: The deepest known permafrost is in Yakutia, eastern Siberia, where it extends to approximately 1,500 m below the surface — a legacy of the extremely cold Pleistocene conditions. Current permafrost in this region is typically 300–600 m deep.

The Active Layer

The active layer is the surface layer of ground above the permafrost that thaws seasonally during the summer months and refreezes in winter.

• Typically 0.5–3 m thick in most periglacial environments
• Depth depends on summer temperatures, vegetation cover, snow cover, soil type, and aspect
• The active layer is where most periglacial geomorphological processes operate
• When the active layer thaws, the water cannot drain downward through the impermeable permafrost below, so the ground becomes waterlogged — this is critical for processes like solifluction

graph TD
    A["Surface: Vegetation / exposed ground"] --> B["Active Layer<br/>0.5–3 m thick<br/>Thaws in summer, refreezes in winter"]
    B --> C["Permafrost Table<br/>(upper boundary of permafrost)"]
    C --> D["Permafrost<br/>Permanently frozen ground<br/>Extends to tens or hundreds of metres depth"]
    D --> E["Unfrozen ground below<br/>(geothermal heat)"]

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Periglacial Processes

1. Freeze-Thaw Weathering (Frost Shattering)

The most fundamental periglacial process:

• Water enters cracks and pores in rock and soil
• When temperature drops below 0°C, water freezes and expands by approximately 9%
• Repeated cycles of freezing and thawing shatter rock into angular fragments
• Most effective where temperatures oscillate frequently around 0°C (between about −3°C and −8°C)
• Produces extensive scree (talus) slopes and blockfields (felsenmeer) — surfaces covered with angular rock fragments
• The Stiperstones, Shropshire — a striking blockfield of quartzite tors and angular debris formed by periglacial freeze-thaw action during the Devensian cold stage

2. Frost Heave

• Water in the soil freezes, forming ice lenses — layers of ice that grow as water is drawn upward through capillary action toward the freezing front
• The growing ice lenses push the soil surface upward (heaving)
• Coarser particles are pushed upward and outward more rapidly than finer particles (due to their higher thermal conductivity), leading to sorting
• This process is fundamental to the formation of patterned ground

3. Solifluction

Solifluction is the slow, downslope movement of waterlogged soil and regolith over an impermeable surface.

• In periglacial environments, this is specifically called gelifluction — solifluction caused by thawing of the active layer over impermeable permafrost
• The thawed active layer becomes saturated (water cannot drain through the frozen permafrost below)
• Even on very gentle slopes (as low as 1–2°), the saturated soil flows slowly downslope
• Typical rates: 1–10 cm per year
• Produces distinctive solifluction lobes and solifluction sheets — tongue-shaped or sheet-like features on hillslopes
• Head deposits (coombe rock) in southern England are fossil solifluction deposits from the Pleistocene, found in many dry valleys of the chalk downs

4. Nivation

Nivation is a combination of processes (freeze-thaw weathering, chemical weathering, solifluction, and meltwater erosion) operating beneath and around a snow patch: