In geology, permafrost is ground, including rock or (cryotic) soil,
at or below the freezing point of water 0 °C (32 °F) for
two or more years. Most permafrost is located in high latitudes (in
and around the Arctic and Antarctic regions), but at lower latitudes
alpine permafrost occurs at higher elevations. Ground ice is not
always present, as may be in the case of non-porous bedrock, but it
frequently occurs and it may be in amounts exceeding the potential
hydraulic saturation of the ground material.
Permafrost accounts for
0.022% of total water on Earth and exists in 24% of exposed land in
the Northern Hemisphere. It also occurs subsea on the
continental shelves of the continents surrounding the Arctic Ocean,
portions of which were exposed during the last glacial period, with
global weather implications.
A global temperature rise of 1.5 °C (2.7 °F) above current
levels would be enough to start the thawing of permafrost in Siberia,
according to one group of scientists.
1.1 Continuity of coverage
1.1.1 Discontinuous permafrost
1.1.2 Continuous permafrost
1.2 Alpine permafrost
1.3 Subsea permafrost
2.1 Base depth
2.2 Massive ground ice
Carbon cycle in permafrost
Climate change effects
3.1 Historical changes
3.3 Effect on slope stability
3.4 Ecological consequences
3.5 Predicted rate of change in the Arctic
4 Other issues
4.1 Construction on permafrost
4.2 Revival of organisms preserved in permafrost
6 External links
Red lines: Seasonal temperature extremes (dotted=average).
Permafrost is soil, rock or sediment that is frozen for more than two
consecutive years. In areas not overlain by ice, it exists beneath a
layer of soil, rock or sediment, which freezes and thaws annually and
is called the "active layer". In practice, this means that
permafrost occurs at an average air temperature of -2 °C or
Active layer thickness varies with the season, but is 0.3 to 4
meters thick (shallow along the Arctic coast; deep in southern Siberia
and the Qinghai-Tibetan Plateau). In the Northern Hemisphere, 24% of
the ice-free land area, equivalent to 19 million square kilometers,
is more or less influenced by permafrost. Most of this area is found
in Siberia, northern Canada,
Alaska and Greenland. Beneath the active
layer annual temperature swings of permafrost become smaller with
depth. The deepest depth of permafrost occurs where geothermal heat
maintains a temperature above freezing. Above that bottom limit there
may be permafrost, whose temperature doesn't change
The extent of permafrost varies with the climate. Today, a
considerable area of the Arctic is covered by permafrost (including
discontinuous permafrost). Overlying permafrost is a thin active layer
that seasonally thaws during the summer.
Plant life can be supported
only within the active layer since growth can occur only in soil that
is fully thawed for some part of the year. Thickness of the active
layer varies by year and location, but is typically 0.6–4 m
(2.0–13.1 ft) thick. In areas of continuous permafrost and
harsh winters, the depth of the permafrost can exceed 1,400 m
Permafrost can also store carbon, both as peat
and as methane. Work investigating the permafrost carbon pool size
estimates that 1400–1700 Gt of carbon is stored in the northern
circumpolar permafrost region. While a recent study that includes
stores of the Tibetan Plateau, estimates total carbon pools in the
permafrost of the
Northern Hemisphere to be 1832 Gt. This large
carbon pool represents more carbon than currently exists in all living
Excavating ice-rich permafrost with a jackhammer in Alaska.
Continuity of coverage
Permafrost typically forms in any climate where the mean annual air
temperature is less than the freezing point of water. Exceptions are
found in moist-wintered forest climates, such as in Northern
Scandinavia and the North-Eastern part of European Russia west of the
Urals, where snow acts as an insulating blanket. Glaciated areas may
be exceptions. Since all glaciers are warmed at their base by
geothermal heat, temperate glaciers, which are near the
pressure-melting point throughout, may have liquid water at the
interface with the ground and are therefore free of underlying
permafrost. "Fossil" cold anomalies in the
Geothermal gradient in
areas where deep permafrost developed during the
down to several hundred metres. This is evident from temperature
measurements in boreholes in
North America and Europe.
Typically, the below-ground temperature varies less from season to
season than the air temperature, with mean annual temperatures tending
to increase with depth. Thus, if the mean annual air temperature is
only slightly below 0 °C (32 °F), permafrost will form
only in spots that are sheltered—usually with a northerly
aspect—creating discontinuous permafrost. Usually, permafrost will
remain discontinuous in a climate where the mean annual soil surface
temperature is between −5 and 0 °C (23 and 32 °F). In
the moist-wintered areas mentioned before, there may not be even
discontinuous permafrost down to −2 °C (28 °F).
Discontinuous permafrost is often further divided into extensive
discontinuous permafrost, where permafrost covers between 50 and 90
percent of the landscape and is usually found in areas with mean
annual temperatures between −2 and −4 °C (28 and
25 °F), and sporadic permafrost, where permafrost cover is less
than 50 percent of the landscape and typically occurs at mean annual
temperatures between 0 and −2 °C (32 and 28 °F). In
soil science, the sporadic permafrost zone is abbreviated SPZ and the
extensive discontinuous permafrost zone DPZ. Exceptions occur in
Alaska where the present depth of permafrost
is a relic of climatic conditions during glacial ages where winters
were up to 11 °C (20 °F) colder than those of today.
Estimated extent of alpine permafrost by region
1,300 km2 (500 sq mi)
1,000 km2 (390 sq mi)
263 km2 (102 sq mi)
255 km2 (98 sq mi)
251 km2 (97 sq mi)
125 km2 (48 sq mi)
100 km2 (39 sq mi)
Rocky Mountains (US and Canada)
100 km2 (39 sq mi)
75 km2 (29 sq mi)
<100 km2 (39 sq mi)
At mean annual soil surface temperatures below −5 °C
(23 °F) the influence of aspect can never be sufficient to thaw
permafrost and a zone of continuous permafrost (abbreviated to CPZ)
forms. A line of continuous permafrost in the Northern Hemisphere
represents the most southerly border where land is covered by
continuous permafrost or glacial ice. The line of continuous
permafrost varies around the world northward or southward due to
regional climatic changes. In the southern hemisphere, most of the
equivalent line would fall within the
Southern Ocean if there were
land there. Most of the Antarctic continent is overlain by glaciers,
under which much of the terrain is subject to basal melting. The
exposed land of
Antarctica is substantially underlain with
permafrost, some of which is subject to warming and thawing along
Estimates of the total area of alpine permafrost vary. Bockheim and
Munroe combined three sources and made the tabulated estimates by
region, totaling 3,560,000 km2 (1,370,000 sq mi).
Alpine permafrost in the
Andes has not been mapped. Its extent has
been modeled to assess the amount of water bound up in these
areas. In 2009, a researcher from
Alaska found permafrost at the
4,700 m (15,400 ft) level on Africa's highest peak, Mount
Kilimanjaro, approximately 3° north of the equator.
Subsea permafrost occurs beneath the seabed and exists in the
continental shelves of the polar regions. These areas formed during
the last ice age, when a larger portion of Earth's water was bound up
in ice sheets on land and when sea levels were low. As the ice sheets
melted to again become seawater, the permafrost became submerged
shelves under relatively warm and salty boundary conditions, compared
to surface permafrost. Therefore, subsea permafrost exists in
conditions that lead to its diminishment. According to Osterkamp,
subsea permafrost is a factor in the "design, construction, and
operation of coastal facilities, structures founded on the seabed,
artificial islands, sub-sea pipelines, and wells drilled for
exploration and production." It also contains gas hydrates in
places, which are both a "potential abundant source of energy", but
also may destabilize, as subsea permafrost warms and thaws, producing
large amounts of methane gas, which is a potent green-house
Time required for permafrost to reach depth at Prudhoe Bay, Alaska
4.44 m (14.6 ft)
79.9 m (262 ft)
219.3 m (719 ft)
461.4 m (1,514 ft)
567.8 m (1,863 ft)
626.5 m (2,055 ft)
687.7 m (2,256 ft)
Permafrost extends to a base depth where geothermal heat from the
Earth and the mean annual temperature at the surface achieve an
equilibrium temperature of 0 °C. The base depth of
permafrost reaches 1,493 m (4,898 ft) in the northern Lena
Yana River basins in Siberia. The geothermal gradient is the
rate of increasing temperature with respect to increasing depth in the
Earth's interior. Away from tectonic plate boundaries, it is about
25–30 °C/km (72–87 °F/mi) near the surface in most of
the world. It varies with the thermal conductivity of geologic
material and is less for permafrost in soil than in bedrock.
Calculations indicate that the time required to form the deep
permafrost underlying Prudhoe Bay,
Alaska was over a half-million
years. This extended over several glacial and interglacial
cycles of the
Pleistocene and suggests that the present climate of
Prudhoe Bay is probably considerably warmer than it has been on
average over that period. Such warming over the past 15,000 years is
widely accepted. The table to the right shows that the first
hundred metres of permafrost forms relatively quickly but that deeper
levels take progressively longer.
Massive ground ice
Massive blue ground ice exposure on the north shore of Herschel
Island, Yukon, Canada.
When the ice content of a permafrost exceeds 250 percent (ice to dry
soil by mass) it is classified as massive ice. Massive ice bodies can
range in composition, in every conceivable gradation from icy mud to
pure ice. Massive icy beds have a minimum thickness of at least 2 m, a
short diameter of at least 10 m. First recorded North American
observations were by European scientists at Canning River,
1919. Russian literature provides an earlier date of 1735 and 1739
during the Great North Expedition by P. Lassinius and Kh. P. Laptev,
respectively. Two categories of massive ground ice are buried
surface ice and intrasedimental ice (also called constitutional
Buried surface ice may derive from snow, frozen lake or sea ice,
aufeis (stranded river ice) and—probably the most prevalent—buried
Intrasedimental ice forms by in-place freezing of subterranean waters
and is dominated by segregational ice which results from the
crystallizational differentiation taking place during the freezing of
wet sediments, accompanied by water migrating to the freezing
Intrasedimental or constitutional ice has been widely observed and
studied across Canada and also includes intrusive and injection
Additionally, ice wedges—a separate type of ground ice—produce
recognizable patterned ground or tundra polygons. Ice wedges form in a
pre-existing geological substrate and were first described in
Several types of massive ground ice, including ice wedges and
intrasedimental ice within the cliff wall of a retrogressive thaw
slump located on the southern coast of Herschel Island within an
approximately 22-metre (72 ft) by 1,300-metre (4,300 ft)
Permafrost processes manifest themselves in large-scale land forms,
such as palsas and pingos and smaller-scale phenomena, such as
patterned ground found in arctic, periglacial and alpine areas.
A group of palsas, as seen from above, formed by the growth of ice
Pingos near Tuktoyaktuk, Northwest Territories, Canada
Stone rings on Spitsbergen
Ice wedges seen from top
Solifluction on Svalbard
Contraction crack (ice wedge) polygons on Arctic sediment.
Cracks forming at the edges of the
Storflaket permafrost bog in
Carbon cycle in permafrost
The permafrost carbon cycle (Arctic
Carbon Cycle) deals with the
transfer of carbon from permafrost soils to terrestrial vegetation and
microbes, to the atmosphere, back to vegetation, and finally back to
permafrost soils through burial and sedimentation due to cryogenic
processes. Some of this carbon is transferred to the ocean and other
portions of the globe through the global carbon cycle. The cycle
includes the exchange of carbon dioxide and methane between
terrestrial components and the atmosphere, as well as the transfer of
carbon between land and water as methane, dissolved organic carbon,
dissolved inorganic carbon, particulate inorganic carbon and
particulate organic carbon.
Climate change effects
Arctic permafrost has been diminishing for many centuries. The
consequence is thawing soil, which may be weaker, and release of
methane, which contributes to an increased rate of global warming as
part of a feedback loop.
Recently thawed Arctic permafrost and coastal erosion on the Beaufort
Sea, Arctic Ocean, near Point Lonely, Alaska. Photo Taken in August,
At the Last Glacial Maximum, continuous permafrost covered a much
greater area than it does today, covering all of ice-free
Szeged (southeastern Hungary) and the
Sea of Azov
Sea of Azov (then dry
East Asia south to present-day
Abashiri. In North America, only an extremely narrow belt of
permafrost existed south of the ice sheet at about the latitude of New
Jersey through southern
Iowa and northern Missouri, but permafrost was
more extensive in the drier western regions where it extended to the
southern border of
Idaho and Oregon. In the southern hemisphere,
there is some evidence for former permafrost from this period in
Otago and Argentine Patagonia, but was probably discontinuous,
and is related to the tundra. Alpine permafrost also occurred in the
Drakensberg during glacial maxima above about 3,000 metres
See also: Thermokarst
Permafrost thaw ponds on peatland in Hudson Bay, Canada in 2008.
The ground can consist of many substrate materials, including bedrock,
sediment, organic matter, water or ice. Frozen ground is that which is
below the freezing point of water, whether or not water is present in
the substrate. Ground ice is not always present, as may be the case
with nonporous bedrock, but it frequently occurs and may be present in
amounts exceeding the potential hydraulic saturation of the thawed
By definition, permafrost is ground that remains frozen for two or
more years. Since frozen soil, including permafrost, comprises a large
percentage of substrate materials other than ice, it thaws rather than
melts even as any ice content melts. An analogy is when a freezer
door is left open, although the ice in the freezer may change phase to
a liquid, the food solids will not experience a phase change. In
aggregate, the food thaws but does not melt. Melting implies the phase
change of all solids to liquid. One visible sign of permafrost
degradation is the random displacement of trees from their vertical
orientation in permafrost areas.
As a consequence, precipitation has increased which in turn results in
the weakening and eventual collapse of buildings in areas such as
Norilsk in northern Russia, which lies upon the permafrost.
Effect on slope stability
Over the past century, an increasing number of alpine rock slope
failure events in mountain ranges around the world have been recorded.
It is expected that the high number of structural failures is due to
permafrost thawing, which is thought to be linked to climate change.
Permafrost thawing is thought to have contributed to the 1987 Val Pola
landslide that killed 22 people in the Italian Alps. In mountain
ranges, much of the structural stability can be attributed to glaciers
and permafrost. As climate warms, permafrost thaws, which results in a
less stable mountain structure, and ultimately more slope
McSaveney  reported massive rock and ice falls (up to 11.8 million
m3), earthquakes (up to 3.9 Richter), floods (up to 7.8 million m3
water), and rapid rock-ice flow to long distances (up to 7.5 km
at 60 m/s) caused by “instability of slopes” in high mountain
permafrost. Instability of slopes in permafrost at elevated
temperatures near freezing point in warming permafrost is related to
effective stress and buildup of pore-water pressure in these
soils. Kia and his co-inventors  invented a new filter-less
rigid piezometer (FRP) for measuring pore-water pressure in partially
frozen soils such as warming permafrost soils. They extended the use
of effective stress concept to partially frozen soils for use in slope
stability analysis of warming permafrost slopes. The use of effective
stress concept has many advantages such as ability to extend the
concepts of "Critical State
Soil Mechanics" into frozen ground
Worldwide, permafrost contains 1700 billion tons of organic material
equaling almost half of all organic material in all soils. This
pool was built up over thousands of years and is only slowly degraded
under the cold conditions in the Arctic. The amount of carbon
sequestered in permafrost is four times the carbon that has been
released to the atmosphere due to human activities in modern time.
One manifestation of this is yedoma, which is an organic-rich (about
2% carbon by mass) Pleistocene-age loess permafrost with ice content
of 50–90% by volume.
Formation of permafrost has significant consequences for ecological
systems, primarily due to constraints imposed upon rooting zones, but
also due to limitations on den and burrow geometries for fauna
requiring subsurface homes. Secondary effects impact species dependent
on plants and animals whose habitat is constrained by the permafrost.
One of the most widespread examples is the dominance of Black Spruce
in extensive permafrost areas, since this species can tolerate rooting
pattern constrained to the near surface.
One gram of soil from the active layer may include more than one
billion bacteria cells. If placed along each other, bacteria from one
kilogram of active layer soil will form a 1000 km long chain. The
number of bacteria in permafrost soil varies widely, typically from 1
to 1000 million per gram of soil. Most of these bacteria and fungi
in permafrost soil can not be cultured in the laboratory, but the
identity of the microorganisms can be revealed by DNA-based
The Arctic region is one of the many natural sources of the greenhouse
gas methane. Global warming accelerates its release, due to both
release of methane from existing stores, and from methanogenesis in
rotting biomass. Large quantities of methane are stored in the
Arctic in natural gas deposits, permafrost, and as submarine
Permafrost and clathrates degrade on warming, thus large
releases of methane from these sources may arise as a result of global
warming. Other sources of methane include submarine taliks,
river transport, ice complex retreat, submarine permafrost and
decaying gas hydrate deposits. Preliminary computer analyses
suggest that permafrost could produce carbon equal to 15 percent or so
of today’s emissions from human activities.
A hypothesis forwarded by
Sergey Zimov is that the reduction of herds
of large herbivores has increased the ratio of energy emission and
energy absorption tundra (energy balance) in a manner that increases
the tendency for net thawing of permafrost. He is testing this
hypothesis in an experiment at
Pleistocene Park, a nature reserve in
Predicted rate of change in the Arctic
See also: Arctic methane release
IPCC Fifth Assessment Report there is high confidence
that permafrost temperatures have increased in most regions since the
early 1980s. Observed warming was up to 3 °C in parts of
Alaska (early 1980s to mid-2000s) and up to 2 °C in
parts of the Russian European North (1971–2010). In Yukon, the
zone of continuous permafrost might have moved 100 kilometres
(62 mi) poleward since 1899, but accurate records only go back 30
years. It is thought that permafrost thawing could exacerbate global
warming by releasing methane and other hydrocarbons, which are
powerful greenhouse gases. It also could encourage erosion
because permafrost lends stability to barren Arctic slopes.
Arctic temperatures are expected to increase at roughly twice the
global rate. The Intergovernmental Panel on
Climate Change (IPCC)
will in their fifth report establish scenarios for the future, where
the temperature in the Arctic will rise between 1.5 and 2.5 °C
by 2040 and with 2 to 7.5 °C by 2100. Estimates vary on how many
tons of greenhouse gases are emitted from thawed permafrost soils. One
estimate suggests that 110–231 billion tons of CO2 equivalents
(about half from carbon dioxide and the other half from methane) will
be emitted by 2040, and 850–1400 billion tons by 2100. This
corresponds to an average annual emission rate of 4–8 billion tons
of CO2 equivalents in the period 2011–2040 and annually 10–16
billion tons of CO2 equivalents in the period 2011–2100 as a result
of thawing permafrost. For comparison, the anthropogenic emission of
all greenhouse gases in 2010 is approximately 48 billion tons of CO2
equivalents. Release of greenhouse gases from thawed permafrost to
the atmosphere may increase global warming.
International Permafrost Association
International Permafrost Association (IPA) is an integrator of
issues regarding permafrost. It convenes International Permafrost
Conferences, undertakes special projects such as preparing databases,
maps, bibliographies, and glossaries, and coordinates international
field programmes and networks. Among other issues addressed by the IPA
are: Problems for construction on permafrost owing to the change of
soil properties of the ground on which structures are placed and the
biological processes in permafrost, e.g. the preservation of organisms
frozen in situ.
Construction on permafrost
Building on permafrost is difficult because the heat of the building
(or pipeline) can thaw the permafrost and destabilize the structure.
Three common solutions include: using foundations on wood piles;
building on a thick gravel pad (usually 1–2 metres/3.3–6.6 feet
thick); or using anhydrous ammonia heat pipes. The Trans-Alaska
Pipeline System uses heat pipes built into vertical supports to
prevent the pipeline from sinking and the
Qingzang railway in Tibet
employs a variety of methods to keep the ground cool, both in areas
with frost-susceptible soil.
Permafrost may necessitate special
enclosures for buried utilities, called "utilidors".
Permafrost Research Institute in Yakutsk, found that the sinking
of large buildings into the ground can be prevented by using pile
foundations extending down to 15 metres (49 ft) or more. At this
depth the temperature does not change with the seasons, remaining at
about −5 °C (23 °F).
Modern buildings in permafrost zones may be built on piles to avoid
permafrost-thaw foundation failure from the heat of the building.
Heat pipes in vertical supports maintain a frozen bulb around portions
of the Trans-
Alaska Pipeline that are at risk of thawing.
Above-ground utility lines in a permafrost zone avoid thawing of
Pile foundations in Yakutsk, a city underlain with continuous
Revival of organisms preserved in permafrost
In 2012, Russian researchers have proved that permafrost can serve as
a natural depository for ancient life forms by reviving of Silene
stenophylla from 30,000 year old tissue found in an
Ice Age squirrel
burrow in the
Siberian permafrost. This the oldest plant tissue ever
revived. The plant was fertile, producing white flowers and viable
seeds. The study demonstrated that tissue can survive ice preservation
for tens of thousands of years. A 2016 outbreak of anthrax in the
Yamal Peninsula is believed to be due to thawing permafrost.
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Wikimedia Commons has media related to Permafrost.
Permafrostwatch University of
International Permafrost Association
International Permafrost Association (IPA)
Center for Permafrost
Map of permafrost in Antarctica.
Permafrost – what is it? – YouTube (Alfred Wegener Institute)
Solifluction lobes and sheets
Soils and deposits
Stratified slope deposit
Biomes and ecotones
Arctic tree line
Montane grasslands and shrublands
Alpine tree line (Massenerhebung effect)
Taiga (Drunken trees)