Key features of periglacial environments

Periglacial environments are areas near glaciers or ice sheets where the ground experiences intense freezing and thawing cycles. These conditions lead to unique processes that shape the landscape, often in regions with permafrost.

Formation and characteristics of ice wedges

Ice wedges are vertical cracks in the ground filled with ice, forming in permafrost areas due to repeated freezing and thawing. They often create polygonal patterns visible on the surface.

How ice wedges develop

1. In winter, extreme cold causes the ground to contract through a process called frost contraction, forming cracks that extend into the permafrost.
2. In spring, the active layer thaws, producing meltwater that flows into these cracks.
3. The water freezes within the cracks because the underlying permafrost remains frozen, creating initial ice wedges.
4. In subsequent winters, frost contraction reopens the same cracks, splitting the existing ice.
5. More meltwater enters and freezes, gradually widening the wedges over time.

This repeated cycle can produce large polygonal shapes on the land surface, with trenches outlining the patterns. These features are common in places like Svalbard, where they appear as networks of cracks in grassy landscapes.

Processes creating patterned ground

Patterned ground refers to arrangements of stones on the permafrost surface, forming circles, polygons, or stripes. These patterns emerge from natural sorting processes driven by freezing and thawing.

Ways patterned ground forms

• Through frost heave:
  • Water beneath stones freezes and expands, pushing the stones upwards to the surface.
  • The stones then roll to the edges of the resulting mounds, creating circles.
  • When mounds are close together, they form polygons. On slopes, stones roll downhill, producing striped lines.
• Through frost contraction:
  • The ground cracks into polygonal shapes due to contraction in cold conditions.
  • Stones fill these cracks, raising them above the surface and outlining the patterns.

Types and formation of pingos

A pingo is a dome-shaped hill with a core of ice, reaching up to 85 metres high and 480 metres wide. Pingos form in permafrost regions and can develop craters if the ice melts.

Open-system pingos

• Open-system pingos occur in areas of discontinuous permafrost, where gaps exist between frozen sections.

• Groundwater from deeper unfrozen layers is forced upwards through these gaps.

• The water accumulates and freezes, forming an ice core.

• This expanding ice pushes the overlying ground upwards, creating a conical dome.

Closed-system pingos

• Closed-system pingos form in continuous permafrost areas, often starting beneath a lake.

• The lake insulates the ground, keeping the soil beneath it unfrozen while surrounding areas are permafrost.

• When the lake dries up, the insulation is lost, and permafrost advances around the unfrozen zone.

• Water collects in the centre of this unfrozen area and eventually freezes into an ice core.

• The growing ice lifts the ground above, forming the pingo.

If the ice core melts, a depression or crater may appear at the top, sometimes filling with meltwater.

Aeolian processes and loess fields

Aeolian processes involve wind action that transports and deposits fine sediments in periglacial landscapes.

Formation of loess fields

• Loess fields are vast deposits of wind-blown silt, often originating from glacial outwash plains where fine materials are eroded.

• Strong winds carry the silt (loess) across open plateaus, unobstructed by vegetation like large trees.

• The sediment settles in thick layers.

• In warmer periglacial margins, this loess enhances soil quality, supporting arable farming.

Case study: Tundra environment of Northern Canada

The tundra in Northern Canada exemplifies periglacial landscapes, covering areas from Yukon in the west to Hudson Bay and Labrador in the east. Permafrost affects 40–50% of Canada, with a mix of lowlands and mountains promoting diverse features.

Key periglacial features

• Patterned ground - Abundant across the region, particularly in the Mackenzie River Delta.
• Pingos - More than 1,350 exist in the Northwest Territories, including Ibyuk, which is 49 metres tall and more than 950 years old. These form in clusters, visible in aerial views around places like Tuktoyaktuk.

Climate and vegetation

• The climate features short growing seasons, often less than two months in northern areas, with temperatures ranging from about -25°C in January to 15°C in July.

• Rainfall is low, peaking in summer.

• Vegetation is limited to low-lying plants like mosses, grasses, and sedges, adapted to the harsh conditions.

• Fauna includes species such as musk oxen and Arctic hares, which have evolved to survive the cold.

Human impacts and threats

• Rising temperatures may thaw permafrost, releasing stored carbon as carbon dioxide and accelerating global warming.
• While people live throughout the tundra, protected areas like National Wildlife Areas help manage and conserve the landscape.