What Is Permafrost? Definition, Types, and Examples

Is permafrost melting? Environmental and economic consequences

permafrost in the snow high icy land,
Vitaly Faritovich / Getty Images

Permafrost is frozen ground — which can include sand, soil, or rocks— that stays frozen for at least two years straight. It can be on land, but it can also be found under the ocean. Some permafrost has been frozen for hundreds or even thousands of years, but it's different from ground that freezes in the winter and thaws in the summer. Permafrost stays frozen through seasonal changes.

Permafrost can been a few feet deep, or much deeper. In some locations the permafrost is over a mile deep. It's found covering huge areas, like the entire Arctic tundra, but it can also be found in smaller, specific spots, like the leeward side of a mountain or a mountaintop.

In the Northern Hemisphere, where there is more landmass, about a quarter of the ground is permafrost. It's in many of the places you might expect to find it, like Canada, Greenland, and the northern regions of Siberia, and under the floor of the Arctic Ocean. Almost 90% of the land in Alaska is permanently frozen. But you'll also find permafrost at high elevations in places you might not expect, like mountaintops in the Rockies and Tibet. In the Southern Hemisphere, it's found in the Andes Mountains and the Southern Alps of New Zealand. 

Permafrost Definition

Permafrost was first named in English by Simeon William Mueller in a 1943 United States Geological Survey (USGS) report, but it had been noted before by others. Mueller got much of his information from 19th century Russian engineering reports, as permafrost had to be dealt with when constructing the Trans-Siberian railway.

Permafrost can be found beneath layers of ice, so that the permafrost layer begins where the ice ends, but it can also be found under what scientists call an "active layer." That's the layer of soil, sand, rocks, or a mix of those that might freeze and thaw seasonally or monthly in response to weather conditions like rain or sunny days. In the case of an active layer, you'd have to dig down about a foot or more to find the permafrost below.

That means that there are areas where permafrost exists right at the surface, below an active layer, or below ice or snow layers that might vary during the course of the year (the permafrost could be below snow for part of the year and exposed part of the year). Those changes could be seasonal, impacted by weather or geothermal action, and other factors.

Usually, permafrost is only found in places where the mean annual air temperatures are low — at or below the freezing point of water: 32 F (0 Celsius). But again, unique local and historical conditions can mean that permafrost might be found in places where mean temperatures are higher.

Permafrost
skif / Getty Images

Continuous Permafrost

When mean soil temperatures are 23 F (-5 C), it's cold enough that the ground stays continually frozen. When 90%-100% of a landscape's ground is frozen, it's called continuous permafrost. There's a line of continuous permafrost in the Northern Hemisphere, which represents the southernmost points at which the land is covered by permafrost (or glacial ice). There's no Southern Hemisphere equivalent because the area where the line would be is under the ocean.

Discontinuous Permafrost

Discontinuous permafrost occurs when 50%-90% of the ground remains frozen. This happens when the ground stays cold but air temperatures fluctuate seasonally. In these cases, average air temperatures are above 23 F (-5 C) but a bit below 32 F (0 Celsius), leading to areas where some soil layers will melt during the summer, while other shaded or protected areas might remain frozen.

Sporadic Permafrost

When the permafrost of an area is less than 50% (usually found where mean annual temperatures are between 32 F and 28 F), it's sporadic permafrost. This happens in similar places as discontinuous permafrost, but perhaps at slightly lower elevations, or in areas exposed to more sun or warm air currents.

Types of Permafrost

Some other subsets of permafrost describe the areas where they are found, rather than their extent.

Ice under permafrost soil in Spitzbergen
SeppFriedhuber / Getty Images

Alpine

Most alpine permafrost is discontinuous, since it happens at higher elevations and there are local weather conditions and geological features that can impact it. Alpine permafrosts can occur anywhere that's cold enough, so they're not isolated to near-polar areas. In 2009, for example, researchers found permafrost on Mt. Kilimanjaro in Africa, which is just about 200 miles from the equator. It was found near the top of the mountain in an area that was unglaciated.

The extent of alpine permafrosts is of interest to scientists because they contain fresh water bound up in the soil. When permafrost melts, that could release water into ecosystems, including ancient water, but much is still not known — the permafrost in the Andes Mountains hasn't been mapped, for example.

Subsea

Subsea permafrost is buried under the seabed in polar areas. These permafrosts are ancient, having formed during the last ice age, when sea levels were lower. As sea levels rose when the ice sheets on land melted, they covered this frozen land with sea water. The permafrost became permanently submerged and remains today, where it can complicate underwater drilling or the installation of undersea pipelines.

Soil Formations

There are a number of interesting soil formations created in permafrost environments linked to the combination and effects of water that expands and contracts as it freezes and melts interacting with local soils, rocks, and sand.

Polygons

Aerial of polygons on the tundra
Tundra of the Arctic North Slope of Alaska in the National Petroleum Reserve. Patrick J. Endres / Getty Images

Seen from an aerial point of view, polygons look like the landscape is one big jigsaw puzzle. They are formed over the seasons when cold winter temperatures cause soil to contract. As it does, it makes cracks; those fissures then fill with spring meltwater (from a nearby mountain's snowpack melting, for instance). Because of the cold permafrost below the original soils the water flows into, the water freezes and expands, forming wedges of ice. This cycle can repeat over years, and each time the cracks get deeper; at some point, the wedges get so thick that they push the soil into ridges that look like polygons.

Pingos

Eastern Siberia Permafrost
Orchidpoet / Getty Images

If you didn't know what they were when looking at them, you'd probably just think that a pingo was a nicely rounded hill. But in areas with permafrost, they are a bit deceptive, since while they are made from soil on the outside, inside they have a core of solid ice. They can be more like mounds just 10 feet tall and a bit wider at the base, or they can be fairly large, a couple hundred feet tall. According to a study published in the journal The Cryosphere, there are an estimated 11,000 pingos on Earth, most of them in the tundra bioclimatic zone.

Solifluction

Solifluction is a collective name for gradual mass wasting slope processes related to freeze-thaw activity. Solifluction lobes and sheets are types of slope failure and landforms. Mass movement of soil affected by alternate freezing and thawing. Characte
Gerald Corsi / Getty Images

Solifluction is an umbrella term for several processes in which an upper layer of the ground moves over frozen ground below it. The permafrost acts like a hard, impermeable surface, so when the soil or sand above it is saturated with liquid, it slowly slides down a slope, pulled by gravity. There are a few different types of solifluction, and there's evidence to suggest the process may even been seen on Mars.

Thermokarsts

The Brooks Range and cloudy sky's reflected in a thermokarst in Alaska's Arctic National Wildlife Refuge.
Shelley Wales / Getty Images

Karst usually refers to a limestone or process containing that rock, but in this case limestone isn't involved — it just looks like a similar process that's seen in limestones. Thermokarsts are formed by frost heaves, which push up small domes of the active layer that lies above permafrost. The domes collapse when warming occurs, leaving behind a concave pucker. From these formations, pingos can develop. In some cases, very large thermokarsts can develop, and when they fill with water, they can become small ponds or even lakes.

Is the Permafrost Melting?

Currently, permafrost covers some huge areas of land (in the Northern Hemisphere, it's estimated at 9 million square miles, the size of the U.S., Canada, and China combined), but it's shrinking.

Because the Arctic is warming about twice as fast as more temperate areas and permafrost is sensitive to even small changes in temperature, permafrost is melting more rapidly than was expected, surprising scientists. One widely cited study in the journal Nature Climate Change estimates that if the Earth warms to 2 °C above pre-industrial levels (the track we are currently on), permafrost will be reduced by 40%.

Permafrost and the Climate Crisis

Melting permafrost has quite a few effects. First, as it melts, it releases greenhouse gases, especially methane, into the atmosphere. That creates a feedback loop — as more permafrost melts, more warming gases make their way into the atmosphere, and the climate heats up more. Second, melting permafrost has local effects, including destabilizing buildings and transportation systems, and possible destructive flooding or landslide/mudslide events.

In addition to the ecological and economic consequences, communities that live on permafrost have begun to lose buildings, and in some places, entire towns may have to be relocated. In Alaska, Greenland, Canada, and Russia, melting permafrost has led to collapsed or sinking houses and buildings. In Vorkuta, Russia, the structural integrity of 40% of its buildings is compromised, and in Norilsk, a city of 175,000 people, 60% of its buildings are damaged from permafrost thaw and 10% of the city's houses have already been abandoned.

It's also difficult to rebuild due to the shifting subsurface conditions. In many of these places, housing is already scarce, and the majority of those affected are indigenous people whose communities have lived in these areas for thousands of years.

Two abandoned buildings collaping
Two abandoned buildings collapsing together due to changes in permafrost underground. BrianScantlebury / Getty Images

Ecological Consequences

Melting permafrost changes landscapes. As the permafrost thaws, as is happening in the Canadian Arctic, Alaska, Russia, and elsewhere, rich landscapes that once provided food for grizzly bears, caribou, and other animals are disappearing under slumps of soil. This is because the ground gets pushed up and rearranged when the water beneath the surface contracts as the ice within melts. Food plants for animals, like cranberries, blueberries, shrubs, lichens, and other edible plants don't survive the muddy, silty onslaught.

Release of Greenhouse Gases

Permafrost melting, set off by human-caused climate change, could create a dangerous feedback loop. According to a study published in the journal Nature, there are an estimated 1,400 gigatons of carbon in the permafrost in the Arctic alone, and that carbon is being released faster than expected. That's about four times what human beings have released since the beginning of the Industrial Revolution and makes it one of the biggest carbon sinks in the world. If released, this carbon needs to be factored into the global output that scientists use to better understand the future impacts of climate change.

If more greenhouse gases are released from the permafrost as it melts, warming temperatures will accelerate, leading to more gases being released, more permafrost melting, and so on.

Viruses and Bacteria

Certain organisms can live for thousands of years preserved in the ice. The conditions are close to ideal — cold, dark, and low-oxygen environments mean that some of these microscopic cells can survive. Viruses, fungi, and bacteria that have been frozen in permafrost could become active when they are flushed into water supplies via melting water.

This already occurred in 2016, when an anthrax-carrying reindeer that had been buried in permafrost for 75 years unfroze. The anthrax got into the water supply and dozens were sickened, a young boy died, and thousands of reindeer also perished, according to a study published in the journal Plos One. The 1918 Spanish flu virus was also found on intact corpses found in Alaska, and even some 40,000-year-old worms came back to life after being unfrozen. The full extent of contamination that could occur from ancient viruses and bacteria lurking in permafrost is unknown.

Economic Impact

For the indigenous peoples, like the Inuit, who live in areas with melting permafrost, it's going to be increasingly difficult to find food because of the thousands of slumps and thermokarst landslides that have already occurred and will occur over the coming years. Those landform changes can alter seashores via collapse, can change how and where streams flow, and can result in lakes draining. All these phenomena can also have negative consequences for the wildlife in the area, which the people depend on.

Permafrost melting also leads to building and road collapse, which need to be rebuilt or abandoned, as well as any commercial activity, from oil and gas drilling, to oil pipelines and any other business or community that depends on stable ground and a reliable water supply. Because of its broad impact, an exact dollar amount to ascribe to melting permafrost is difficult to estimate.

Other Consequences

Melting permafrost is likely to turn up the remains of ancient civilizations, animals, and Earth history that has been buried for thousands of years. A 3,000-year-old Siberian prince's tomb has already been discovered in a remote area, a boon for archeologists who study that time and place.

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