Permanently frozen subsoil, occurring throughout the Polar Regions and locally in perennially frigid areas.
[PERMA(NENT) + FROST.]
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Permanently frozen subsoil, occurring throughout the Polar Regions and locally in perennially frigid areas.
[PERMA(NENT) + FROST.]
Perennially frozen ground, occurring wherever the temperature remains below 32°F (0°C) for several years, whether the ground is actually consolidated by ice or not and regardless of the nature of the rock and soil particles of which the earth is composed. Perhaps 25% of the total land area of the Earth contains permafrost; it is continuous in the polar regions and becomes discontinuous and sporadic toward the Equator. During glacial times permafrost extended hundreds of miles south of its present limits in the Northern Hemisphere.
Temperature of permafrost at the depth of no annual change, about 30–100 ft (10–30 m), crudely approximates mean annual air temperature. It is below 23°F (−5°C) in the continuous zone, between 23–30°F (−5 and −1°C) in the discontinuous zone, and above 30°F (−1°C) in the sporadic zone. Temperature gradients vary horizontally and vertically from place to place and from time to time.
Ice is one of the most important components of permafrost, being especially important where it exceeds pore space. Physical properties of permafrost vary widely from those of ice to those of normal rock types and soil. The cold reserve, that is, the number of calories required to bring the material to the melting point and melt the contained ice, is determined largely by moisture content.
Permafrost develops today where the net heat balance of the surface of the Earth is negative for several years. Much permafrost was formed thousands of years ago but remains in equilibrium with present climates. Permafrost eliminates most groundwater movement, preserves organic remains, restricts or inhibits plant growth, and aids frost action. It is one of the primary factors in engineering and transportation in the polar regions.
Areas of rock and soil where temperatures have been below freezing point for at least two years. Permafrost need contain no ice; a sub-zero temperature is the sole qualification. Any water present need not be frozen since the presence of dissolved minerals lowers the freezing point of water. In epigenetic permafrost ground ice develops mainly in upper parts, vertical freezing dominates, and cryogenic textures develop as water migrates under pressure to the freezing front, so that pressure is exerted on the ground leading to deformation. See involution. In syngenic permafrost the ground ice is regularly distributed throughout the whole thickness of the permafrost; cryogenic textures develop as permafrost grows upwards, and sediments above are not contorted. The growth of permafrost is permafrost aggradation, which decreases the thickness of the active layer and may be caused by the freezing of taliks. It is responsible for the formation of pingos. The decline of permafrost is permafrost degradation, which plays a key role in the development of thermokarst. Permafrost is a very sensitive system; small mistakes in constructing buildings in this environment can have catastrophic effects because of thermo-erosion and thermo-abrasion. Permafrost features are well preserved in the chalklands of southern England.
The permafrost zones of periglacial areas are of two types: continuous permafrost is present in all localities apart from small, localized thawed zones, while discontinuous permafrost exists as small, scattered areas of permanently frozen ground. A frost table marks the upper limit of permafrost, which is overlain by the active layer. See also talik.
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Permanently frozen soil, subsoil, or other deposits in arctic or subarctic regions.
More or less permanently frozen ground represented as a zone up to 3m deep the surface of which undergoes seasonal freezing and thawing. Common in periglacial conditions, the effects of permafrost in the creation of geomorphological features such as ice-wedges, involutions, and pingos have important implications for archaeology because they are sometimes confused with anthropogenic features.
(DOD) Permanently frozen subsoil.
In geology, permafrost or permafrost soil is soil at or below the freezing
point of water (0°C or 32°
The extent of permafrost can vary as the climate changes. Today, approximately 20% of the Earth's land mass is covered by permafrost (including discontinuous permafrost) or glacial ice. 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 to 12 feet) thick. In areas of continuous permafrost and harsh winters the depth of the permafrost can be as much as 1493 m (4510 feet) in the northern Lena and Yana River basins in Siberia.
Permafrost will typically form 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 North-Eastern Russia west of the Urals, where snow acts as an insulating blanket. The bottoms of glaciers can also be free of permafrost, although this is not common.
Typically, the ground temperature will be less variable from season to season than the air temperature, with 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. 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 (23 to 32°F). In the moist-wintered areas mentioned before, there may not be even discontinuous permafrost down to −2 °C. 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.
There are exceptions in unglaciated Siberia and 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. 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. There are also "fossil" cold anomalies in the Geothermal gradient in areas where deep permafrost developed during the Pleistocene that still persists down to several hundred metres. The Suwałki cold anomaly in Poland led to the recognition that similar thermal disturbances related to Pleistocene-Holocene climatic changes are recorded in boreholes throughout Poland. [1]
A line of continuous permafrost in the Northern Hemisphere (Frozen Ground 28, 2004, p5) is formed from the most northerly 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, most of the equivalent line would fall within the Southern Ocean if there were land there. Most of the Antarctic continent is covered with glacial ice, not frozen soil.
Measurement of the depth and extent of permafrost may be an indicator of global
warming as recent years (1998 and 2001) have seen record
thawing of permafrost in Alaska and Siberia. This thawing has led to stands of trees falling, labelled
At the Last Glacial Maximum, continuous permafrost covered a much greater area than it does today, covering all of ice-free Europe south to about Szeged and the Sea of Azov (then dry land) and China south to Beijing. 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. In the southern hemisphere, there is some evidence for former permafrost from this period in central Otago and Argentine Patagonia, but was probably discontinuous.
| Time (yr) | Permafrost Depth (m) |
|---|---|
| 1 | 4.44 (0.002759 mi.) |
| 350 | 79.9 (0.049648 mi.) |
| 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 is 500,740 years. This time extends 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. [2] The table to the right shows that the first hundred metres of permafrost forms relatively quickly but that deeper levels take progressively longer.
Building on permafrost is difficult due to the heat of the building (or pipeline) melting the permafrost and sinking. This problem has three common solutions. Using foundations on wood piles, building on a thick gravel pad (usually 1-2 meters/3.3-6.6 feet thick), or using anhydrous ammonia heat pipes. The Trans-Alaska Pipeline System uses insulated heat pipes to prevent the pipeline from sinking. Qingzang railway in Tibet was built using a variety of methods to keep the ground cool.
At the Permafrost Research Institute in Yakutsk, it has been found that the sinking of large buildings into the ground (known to the Yakuts before Yakutsk was founded) can be prevented by using stilts extending down to about fifteen metres or more. At this depth the temperature does not change with the seasons, remaining at about -5°C (23F).
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International Permafrost Association
Permafrost Young Researchers Network
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Dansk (Danish)
n. - permafrost
Nederlands (Dutch)
permanent bevroren ondergrond
Français (French)
n. - permagel, permafrost
Deutsch (German)
n. - Dauerfrostboden
Ελληνική (Greek)
n. - (γεωγρ.) μόνιμα παγωμένο έδαφος ή υπέδαφος
Português (Portuguese)
n. - região polar permanentemente congelada (f)
Русский (Russian)
вечная мерзлота
Español (Spanish)
n. - permagel
Svenska (Swedish)
n. - ständig tjäle
中文(简体) (Chinese (Simplified))
永久冻土层
中文(繁體) (Chinese (Traditional))
n. - 永久凍土層
한국어 (Korean)
n. - (북극 지방의) 영구 동토층
العربيه (Arabic)
(الاسم) تربه متصقعه
עברית (Hebrew)
n. - שכבת אדמה קפואת-עד (בחוג הקוטב)
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