Permafrost Landscapes, Cold Climate Activity, and Melt

Permafrost is ground (soil, rock or sediment) that stays at or below 0 °C for at least two consecutive years, and periglacial landscapes are cold regions beyond the ice with permafrost and freeze-thaw activity that produce features such as ice wedges, patterned ground, pingos and solifluction lobes. In brief: permafrost underlies about a quarter of the land of the Northern Hemisphere. Only a thin surface layer, the active layer, thaws each summer. As the climate warms, permafrost thaws, which damages buildings and roads, changes drainage and releases carbon dioxide and methane that were locked in the frozen ground.

Cold regions are changing faster than most of the planet, and permafrost thaw affects local communities and the global climate. This guide explains permafrost and its distribution, the main periglacial processes and landforms, the effects of melt, compares the landforms in a table, works through calculations, outlines the history of research and corrects common mistakes.

What is permafrost?

Permafrost occurs where the mean annual air temperature is below about −2 to 0 °C, in the Arctic (Siberia, northern Canada, Alaska), on high mountains and in Antarctica. It can be hundreds of meters thick, and more than 1,000 m in parts of Siberia. It is classified as continuous (covering nearly the whole area), discontinuous (patches interrupted by unfrozen ground) or sporadic (isolated patches). The surface active layer thaws in summer, usually to a depth from a few tens of centimeters to a few meters, and freezes again in winter. Because the water cannot drain downward through the frozen ground, the active layer is often saturated, and the surface becomes boggy.

Permafrost is rich in ice, as well as organic matter from plants that died but did not decay in the cold. Scientists estimate that northern permafrost soils contain roughly 1,400 to 1,600 billion tonnes of carbon, nearly twice the amount of carbon in the atmosphere.

What processes shape periglacial landscapes?

• Freeze-thaw weathering: water in cracks freezes and expands by about 9%, splitting rock into angular fragments, which form blockfields (felsenmeer) and scree.
• Frost heave: freezing water draws more water to it and forms ice lenses, which push stones and soil upward and sort material.
• Solifluction: in summer, the saturated active layer flows slowly downslope over the frozen layer below, even on gentle slopes of 2 to 3°, at rates of a few millimeters to centimeters per year. It forms lobes and terraces.
• Nivation: freeze-thaw and meltwater erosion beneath patches of snow, creating hollows.
• Thermal contraction: very cold winters crack the ground, and water fills the cracks and freezes, forming ice wedges.

What landforms are produced?

• Patterned ground: polygons, circles and stripes of stones and soil, made by repeated frost sorting and cracking, often visible from the air.
• Ice wedges: vertical wedges of ice, a few meters deep, which grow year after year and form polygonal networks at the surface.
• Pingos: ice-cored hills up to tens of meters high that form when groundwater freezes and pushes the ground up. When the ice melts, the hill collapses, leaving a crater with a ring. There are thousands in northern Canada, for example in the Mackenzie Delta.
• Thermokarst: an uneven landscape of hollows, sinkholes and lakes made when ground ice melts and the surface collapses.
• Solifluction lobes and blockfields: tongues of soil moved downslope and fields of angular blocks.
• Asymmetric valleys: valleys with one steeper side, because the sun-facing slope thaws and erodes more.

What happens when permafrost melts?

The Arctic is warming at a rate several times faster than the global average, and many permafrost areas are warming and thawing. Consequences include:

• Damage to infrastructure: buildings, roads, railways, airports and pipelines are damaged when the ground sinks. In parts of Siberia and Alaska, houses have cracked, and engineers use elevated foundations and cooling systems.
• Greenhouse gas release: microbes decompose the thawed organic matter and release carbon dioxide, and where the ground is waterlogged, methane, a stronger greenhouse gas. This is a positive feedback that can add to warming. Estimates of the size of this feedback are uncertain, though many studies expect it to be significant over this century.
• Landscape change: new lakes form and others drain, slopes collapse in “retrogressive thaw slumps,” and coasts erode quickly. Gas explosions have created large craters in the Yamal Peninsula since 2014.
• Effects on people and ecosystems: Indigenous communities lose hunting and travel routes, and old stored material, including contaminants and sometimes ancient microbes, may be released.
• Hydrology: water can drain through the thawed ground, changing rivers and wetlands.

Periglacial landforms compared

Worked example: active layer, creep and carbon

The values are hypothetical, to illustrate typical calculations.

1. Change in active layer: the active layer is 0.5 m deep and increases to 0.65 m after warmer summers. The increase is 0.15 m, which is 0.15 ÷ 0.5 = 30%.
2. Volume of newly thawed ground: over an area of 1 km² (1,000,000 m²), the extra thawed volume is 1,000,000 × 0.15 = 150,000 m³.
3. Carbon released: if the thawed soil has a density of 800 kg/m³ and 5% of its mass is carbon, then 150,000 × 800 = 120,000,000 kg of soil contains 0.05 × 120,000,000 = 6,000,000 kg = 6,000 tonnes of carbon. If 10% of this is released in a year, it is 600 tonnes of carbon, which corresponds to 600 × 3.67 = about 2,200 tonnes of carbon dioxide.
4. Solifluction: a lobe moves at 15 mm per year. In 100 years, it moves 15 × 100 = 1,500 mm = 1.5 m.
5. Ice expansion: a rock crack holding 50 cm³ of water gains about 50 × 0.09 = 4.5 cm³ in volume on freezing.
6. Temperature of the ground: if the ground surface temperature rises from −4 °C to −2 °C, it is still frozen, but only 2 °C from the melting point. A further rise of 2 °C would bring it to 0 °C, and any rise beyond that would let it thaw.

How has permafrost research developed?

Russian scientists studied frozen ground from the 19th century, driven by the need to build railways and mines in Siberia, and a permafrost research station was established at Igarka in the 1930s. In North America, research expanded after the Second World War with military and oil projects, such as the building of the Alaska pipeline in the 1970s, which was raised above ground in places to prevent the heat from the pipe thawing the permafrost. Since the 1990s, networks of boreholes have recorded ground temperatures, and many sites show warming. International programs, including the Global Terrestrial Network for Permafrost, monitor changes, and researchers now focus on carbon feedbacks and on helping communities adapt.

Which mistakes are common?

Mistake 1: Thinking that all frozen ground is permafrost

Ground that freezes in winter and thaws in summer is seasonally frozen. Permafrost must remain frozen for at least two years.

Mistake 2: Assuming that all permafrost thaws at the same speed

Thaw depends on ice content, soil, vegetation, snow cover and local temperature. Ice-rich ground collapses, while dry ground thaws gradually.

Mistake 3: Confusing periglacial and glacial

Periglacial areas are cold regions near but not covered by ice. Their features come from freeze-thaw and permafrost, not from moving glaciers.

Mistake 4: Focusing only on methane

Most of the release is carbon dioxide, although methane is more powerful per molecule and can matter in wet areas.