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The Frozen Zone
| Article
# : |
19128 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
1 / 1991 |
1,712 Words |
| Author
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Troy L. Pewe
Troy L. Pewe is professor of geology at Arizona State
University, Tempe, and president of the International
Permafrost Association. He has studied permafrost in the
polar regions and high mountain areas of the world. |
The Alaska Pipeline is known for its role in transporting petroleum from Alaska's vast northern reserves to Valdez in the south. What generally is not known is that it was the most expensive private industry undertaking in the world, costing $8 billion. Of that, $1 billion was spent to understand and overcome the problem of permafrost, a problem that delayed completion of the project for about two years.
In areas where the mean annual air temperature is below freezing, some of the ground frozen in the winter will not completely thaw in the summer; therefore, a layer of perennially frozen ground, or permafrost, will form and continue to grow downward in small increments from the seasonally frozen ground. This layer will become thicker each winter, the thickness being controlled by the thermal balance between the heat flowing upward from the earth's interior and that flowing outward into the atmosphere.
Permafrost affects many of man's activities and causes problems that are not experienced elsewhere. Agriculture, mining, water supply, sewage disposal, and construction are all seriously affected by the subsidence of the ground surface due to permafrost thawing, as well as by associated problems brought on by soil flowage and frost action. Without a thorough understanding of thermal and mechanical problems unique to permafrost, impassable roads, unusable air strips, and abandoned buildings may result.
While permafrost can be the result of the earth's present climate, generally it's a product of a colder past climate. If present surface conditions were to persist for several thousand years, some existing permafrost would thaw out. However, in light of the projected global warming, an event intensified in polar areas, considerable thought is being given to the equilibrium of existing permafrost. Such a global environmental change would greatly increase its thawing rate. Thawing of this type is already being recorded locally in Alaska. Along the southern border of permafrost and in the discontinuous zone, which contain organic-rich soils, trace gases such as carbon dioxide and methane may potentially be released as permafrost thaws from the top down.
Spanning the globe
Permafrost occurs in 82 percent of Alaska, 50 percent of Canada and the Soviet Union, 20 percent of China, and probably all of Antarctica. It is reported to be 1,600 meters thick in northern Siberia and 740 meters thick in northern Alaska, thinning progressively
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