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Permafrost

In geology Geology

Geology anetary geology]] [i] refers to the application of geologic principles to other bodies of the solar... 

, permafrost or permafrost soil is a thermal condition where ground material stays at or below 0C Celsius

The Celsius scale is a temperature [i] scale named after the Swedish [i] astronomer Anders Celsius [i] ... 

 for two or more years. Permafrost is where water is permanently frozen in the soil resulting in minimal or no plant growth. The presence of ice is not necessary, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts excess of the potential hydraulic saturation of the ground material. Most permafrost is located in high latitude Latitude

Latitude, usually denoted symbolically by the Greek letter f [i] , gives the location of a place on ... 

s , but alpine permafrost exists at high altitudes. The extent of permafrost can vary as the climate change Climate change

Climate change refers to the variation in the Earth [i]'s global climate [i] or in regional climates ove ... 

s.

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Encyclopedia

In geology Geology

Geology anetary geology]] [i] refers to the application of geologic principles to other bodies of the solar... 

, permafrost or permafrost soil is a thermal condition where ground material stays at or below 0°C Celsius

The Celsius scale is a temperature [i] scale named after the Swedish [i] astronomer Anders Celsius [i] ... 

 for two or more years. Permafrost is where water is permanently frozen in the soil resulting in minimal or no plant growth. The presence of ice is not necessary, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts excess of the potential hydraulic saturation of the ground material. Most permafrost is located in high latitude Latitude

Latitude, usually denoted symbolically by the Greek letter f [i] , gives the location of a place on ... 

s , but alpine permafrost exists at high altitudes.

The extent of permafrost can vary as the climate change Climate change

Climate change refers to the variation in the Earth [i]'s global climate [i] or in regional climates ove ... 

s. Today, approximately 20% of the Earth Earth

Earth is the third planet [i] in the solar system [i] in terms of distance from the Sun [i], and the fi ... 

's land mass is covered by permafrost or glacial ice Glacier

A glacier is a large, long-lasting river [i] of ice [i] that is formed on land and moves in response to... 

. Seasonal frost commonly overlays permafrost and is called the active layer as it will thaw during the summer. Plant Plant

Plants are a major group of living things [i] including familiar organism [i]s such as tree [i]s, flower [i] ... 

 life can be supported only within the active layer because 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 Metre

The metre, or meter , is a measure of length [i]. ... 

  thick. In areas of continuous permafrost and harsh winters the depth of the permafrost can be very great: 440m at Barrow, Alaska Barrow, Alaska

Barrow is a city in North Slope Borough [i] of the U.S. state [i] of Alaska [i] ... 

,

Continuous and discontinuous permafrost

Permafrost will typically form in any climate Climate

The climate is commonly considered to be the weather [i] averaged over a long period of time, typically ... 

 where the mean annual air temperature is less than the freezing point of water Water

Water is a taste [i]less, odor [i]less substance that is essential to all known forms of life [i] and i ... 

. Exceptions are found in moist-wintered forest climates, such as in Northern Scandinavia and North-Eastern Russia west of Ural, where winter snow acts as an insulating blanket. The bottoms of glaciers can also be free of permafrost, even though this is not the most common situation.

Typically the temperature of the ground will be on average less variable from season to season than the air temperature, and temperatures also tend to increase with depth. Thus, if the mean annual air temperature is only slightly below 0°C , permafrost will form only in spots that are sheltered — usually with a northerly aspect. This creates what is known as discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between -5 and 0 °C . In the moist-wintered areas mentioned before, there may not be even discontinuous permafrost down to -2 °C.

There are exceptions in unglaciated Siberia Siberia

Siberia is a vast region of Russia [i] constituting almost all of Northern Asia [i]. ... 

 and Alaska Alaska

Alaska is a U.S. state [i], located on the northwest tier [i] of North America [i] ... 

 where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 11°C colder than those of today. At mean annual soil surface temperatures below -5°C the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost forms. There are also "fossil" cold anomalies in the Geothermal gradient Geothermal gradient

The geothermal gradient is a ratio describing the rate of heating or cooling of the Earth's top soil and... 

 in areas where deep permafrost developed during the Pleistocene that still persists down to several hundred metres. The Suwalki cold anomaly in Poland led to the recognition that similar thermal disturbances related to Pleistocene-Holocene climatic changes are recorded in boreholes throughout Poland.

A line of continuous permafrost in the Northern Hemisphere Northern Hemisphere

The Northern Hemisphere is the half of a planet's surface that is north [i] of the equator [i] .... 

  is formed from the furthest-northward points at which permafrost sometimes melts or is interrupted by regions without permafrost; north of this line all land is covered by permafrost or glacial ice. The "line" of continuous permafrost lies further north at some longitudes than others and can gradually move northward or southward due to regional climatic changes. In the southern hemisphere Southern Hemisphere

The Southern Hemisphere is the half of a planet's surface that is south [i] of the equator [i].
... 

, most of the equivalent line would fall within the Southern Ocean Southern Ocean

The Southern Ocean, also known as the South Polar Ocean , is the body of water encircling the cont... 

 if there were land there; most if not all of the Antarctic continent Antarctica

Antarctica is the southernmost continent and encompasses the South Pole [i]. ... 

 is covered not with frozen soil but with glacial ice.

Permafrost extent


Measurement of the depth and extent of permafrost may be an indicator of global warming Global warming

Global warming is the observed increase in the average temperature [i] of ... 

 as recent years have seen record thawing of permafrost in Alaska and Siberia. In the Yukon Yukon

The Yukon Territory is one of Canada's [i] northern territories [i], in th ... 

, the zone of continuous permafrost has moved 100 kilometres poleward since 1899. However accurate records only go back 30 years. It is thought that the thawing of permafrost could exacerbate global warming through the release of methane Methane

The simplest hydrocarbon [i], methane, is a gas [i] with a chemical formula [i] of C [i]H [i] ... 

 and other hydrocarbon Hydrocarbon

[i] that consists only of the elements [[carbon]... 

s which are powerful greenhouse gases Greenhouse gas

Greenhouse gases are gas [i]eous components of the atmosphere [i] that contribute to ... 

. It also could encourage erosion Erosion

Erosion is the displacement of solids by the agents of wind, water or ice, by downward or down-slope mo... 

 because permafrost lends considerable stability to the barren slopes in the Arctic.

At the Last Glacial Maximum Last Glacial Maximum

The Last Glacial Maximum refers to the time of maximum extent of the ice sheet [i]s during the last glaciation [i] ... 

, continuous permafrost covered a much greater area than it does today, covering all of ice-free Europe Europe

Europe is one of the seven traditional continent [i]s of the Earth [i]. ... 

 south to about Szeged Szeged

Szeged is the fourth largest city [i] of Hungary [i], the regional centre [i] of South-Eastern Hungary ... 

 and the Sea of Azov Sea of Azov

The Sea of Azov is a northern section of the Black Sea [i], linked to the larger body through the Strait of Kerch [i] ... 

  and China China

China is a cultural region [i] and ancient civilization [i] in East Asia [i]. ... 

 south to Beijing Beijing

Beijing , a city in northern China [i] ... 

. In North America North America

North America is a continent [i] in the Earth [i]'s northern hemisphere [i] and almost fully in the western hemisphere [i]... 

, only an extremely narrow belt of permafrost existed south of the ice sheet Ice sheet

An Ice sheet is a mass of glacier [i] ice that covers surrounding terrain and is greater than 50,000 km [i] ... 

 at about the latitude of New Jersey New Jersey

New Jersey is a state [i] in the Mid-Atlantic [i] and Northeastern [i]... 

 through southern Iowa Iowa

Iowa is a Midwest [i] state [i] of the United States [i]. ... 

 and northern Missouri Missouri

Missouri named after the Missouri Siouan [i] Indian tribe meaning "town of the large canoes", is a cent... 

. In the southern hemisphere, there is some evidence for former permafrost from this period in central Otago Otago

Otago is a region of New Zealand [i] in the south-east of the South Island [i].... 

 and Argentine Argentina

Argentina is a country in southern South America [i]. ... 

 Patagonia Patagonia

Patagonia is the portion of South America [i] in Argentina [i] and Chile [i] made up of the Andes [i] mo ... 

, but it was probably discontinuous.

Time to form deep permafrost

Time taken for permafrost to reach depth
Time Permafrost Depth
1 4.44
350 79.9
3500 219.3
35000 461.4
100000 567.8
225000 626.5
775000 687.7


It has been calculated that the time required to form the deep permafrost underlying Prudhoe Bay, Alaska Prudhoe Bay, Alaska

Prudhoe Bay is a census-designated place [i] located in North Slope Borough [i] ... 

 is 500,740 years. This time extends over several glacial and interglacial cycles of the Pleistocene Pleistocene

The Pleistocene epoch [i] is part of the geologic timescale [i]. ... 

 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.

Construction on permafrost

Building on permafrost is difficult due to the heat of the building melting the permafrost and sinking downwards. This sinking problem has three common solutions: using foundations on wood pile Pile

A pile is one type of building foundation [i].... 

s, building on a thick gravel Gravel

Gravel is rock that is of a certain grain size [i] range. ... 

 pad , or using anhydrous ammonia Ammonia

Ammonia is a compound [i] of nitrogen [i] and hydrogen [i] with the formula [i] ... 

 heat pipes. The Trans-Alaska Pipeline System Trans-Alaska Pipeline System

The Trans-Alaska Pipeline System, usually called the Alyeska Pipeline in Alaska or the Alaska P... 

 uses insulated heat pipes to keep the pipeline from sinking into the permafrost. Qingzang railway Qingzang railway

The Qingzang railway, QinghaiXizang railway, or QinghaiTibet railway, is a railway [i] which ... 

 in Tibet Tibet

Tibet is a region in Central Asia [i] and the home of the Tibetan people [i]. ... 

 was built using a variety of methods to keep the ground cool.

At the Permafrost Research Institute in Yakutsk Yakutsk

Yakutsk is a city in eastern Siberia [i].... 

, it has been found that sinking of large buildings into the frozen earth can be prevented effectively by means of stilts extended down to a depth of about fifteen metres or more. At this depth the temperature does not change with the seasons but remains at about -5°C.

See also

  • Tundra Tundra

    In physical geography [i], tundra is an area where the tree [i] growth is hindered by low temperatures a ... 

  • Gelisols Gelisols

    Gelisols are an order in USA soil taxonomy [i]. ... 

  • Climate change Climate change

    Climate change refers to the variation in the Earth [i]'s global climate [i] or in regional climates ove ... 

  • Global warming Global warming

    Global warming is the observed increase in the average temperature [i] of ... 

  • Global warming controversy Global warming controversy

    The global warming controversy is an ongoing dispute about the effects of humans on the global climate ... 

  • International Permafrost Association International Permafrost Association

    The International Permafrost Association, founded in 1983, has as its objectives to foster the dissemina... 

  • Permafrost Young Researchers Network Permafrost Young Researchers Network

    Objectives


The Permafrost Young Researchers Network is a network formed in 2005 to formally facilitate and st... 


External links

  • , Geological Survey of Canada
  • from *
  • - ENS
  • — BBC





skPermafrost