permafrost

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Related to Discontinuous permafrost: Sporadic permafrost

permafrost,

permanently frozen soil, subsoil, or other deposit, characteristic of arctic and some subarctic regions; similar conditions are also found at very high altitudes in mountain ranges. In 1962 measurements in a borehole drilled on Melville Island, Northwest Territories, Canada, showed that the ground was frozen to a depth of at least 1,475 ft (450 m); comparable thicknesses have been found in other far north regions. Tundrastundra
, treeless plains of N North America and N Eurasia, lying principally along the Arctic Circle, on the coasts and islands of the Arctic Ocean, and to the north of the coniferous forest belt.
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, though underlaid by permafrost, today support centers of population in Alaska, Canada, and Siberia. Permafrost is a very fragile system that may easily be damaged or destroyed by the presence of human-generated heat. A controversy developed in the late 1960s and early 70s over the construction of an oil pipeline from the Alaska North Slope to the southern part of the state. Critics of the project argued that if the pipeline containing hot oil ever came into contact with the permafrost, it would melt the permafrost; the pipeline would then sink and eventually break. The oil spilled during the breakage would result in a major ecological disaster. It was decided to build the pipeline with insulated pipe raised above the permafrost or on gravel beds in order to prevent melting and thus preserve both the pipeline and the ecosystem.

Permafrost

 

a vague term of many meanings applied to the phenomenon of the cooling of rocks on the upper part of the earth’s crust to temperatures of zero and below; the rocks themselves that have hardened as a result of the freezing of the moisture they contained; and the stratum (layer) or zone (region of horizontal spread) of rocks that do not thaw for a long time.

The term “permafrost” was introduced into scientific usage in 1927 by the founder of the school of Soviet geocryologists, M. I. Sumgin, who defined it as ground frost that exists for two to several thousand years. The phrase “ground frost” was not clearly defined in this formulation, and this led to the use of permafrost in various meanings.

As geocryology developed, investigators found themselves increasingly inconvenienced by the word “permafrost,” and as a result it was sharply criticized by P. F. Shevtsov, L. A. Meister, and others in the 1950’s at the V. A. Obruchev Institute of Geocryology of the Academy of Sciences of the USSR. This led to a prolonged discussion of all geocryological terminology. Of the many scientific terms suggested to replace “permafrost,” “perennial frozen rocks” and “perennial cryolithozone” are in widest use.

REFERENCES

Osnovy geokriologii (merzlotovedeniia), parts 1-2. Moscow, 1959.
Materialy po obshchemu merzlotovedeniiu. Moscow, 1959.
Popov, A. I. Merzlotnye iavleniia v zemnoi kore (kriolitologiia). Moscow, 1967.
Dostovalov, B. N., and V. A. Kudriavtsev. Obshchee merzlotovedenie. Moscow, 1967.

A. E. SNOPKOV

permafrost

[′pər·mə‚frȯst]
(geology)
Perennially frozen ground, occurring wherever the temperature remains below 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.

permafrost

Permanently frozen soil, subsoil, or other deposits in arctic or subarctic regions.

permafrost

ground that is permanently frozen, often to great depths, the surface sometimes thawing in the summer
References in periodicals archive ?
These three cases help to confirm our original spatial hypothesis that discontinuous permafrost is more likely to degrade than continuous permafrost.
Statistical analysis of the PSHI map for each of the three test cases revealed that the discontinuous permafrost region is significantly more at risk of thaw subsidence than the continuous permafrost region ([alpha] = 0.
Nevertheless, changing the importance rank does not affect the direction of PSHI; in particular, there was little change in mid-Alaska, which corresponds to the discontinuous permafrost area in Alaska, and the areas at high risk of thaw subsidence (Group 4 and Group 5) are still concentrated in mid-Alaska.
For this second PSHI test, calculated with temperature as the most important variable, the statistical analysis did not prove the hypothesis that discontinuous permafrost areas have greater risk of thaw subsidence than continuous permafrost areas.
A novel technique was used to confirm that the discontinuous permafrost region of Alaska is more at risk of thaw subsidence than the continuous permafrost region.
The 313-mile Donlin pipeline would cross about 100 miles of discontinuous permafrost terrain.
The route avoids all areas of dangerous discontinuous permafrost which maximizes the potential for continual ice build-up under a chilled gas pipeline and resulting heave.
Most favorable onshore terrain (avoids mountains, earthquake zones, major river crossings, steep slopes, forests and discontinuous permafrost zones.
Available ground temperature measurements for the northern Hudson Bay lowland suggest that most of its area is in the discontinuous permafrost zone.
Internal drainage through taliks has also been advanced to explain shrinkage in lake surface area in the discontinuous permafrost zone of Alaska; however, this process seems unlikely to operate in the Old Crow Basin given that the lakes are underlain by glacio-lacustrine clays, which would restrict groundwater circulation even if permafrost were to degrade significantly.

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