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Permafrost

 

Overview

The permafrost tunnel 10 miles north of Fairbanks, Alaska, is called a "chilly, smelly time machine" because it exposes permafrost layers dating from 11,000 to more than 30,000 years ago. These layers contain plant and animal remains whose decay creates the smell. Permafrost underlies an estimated 20%-25% of the world's land surface; it occurs in more than 50% of Russia and Canada, 82% of Alaska, 20% of China, and probably all of Antarctica. Permafrost in northern Siberia is 1,600 meters, (5,250 feet) thick and it is 650 meters (2,100 feet) thick in northern Alaska. The active surface layer of permafrost is a thin slice of tundra vegetation that thaws every summer and freezes in winter. A frozen sublayer keeps the water on the surface. The active layer is vulnerable to environmental damage. For example, tracks from a passing vehicle will tear up the fragile insulating tundra, allowing the soil to thaw into scars that may remain for hundreds of years. Underground, permafrost consists of frozen soils ranging from gravel to silt. Silty soil is made of fine, powdery sedimentary particles. They possess great "wicking" capacities, enabling water to migrate and accumulate in large bodies of ice in the permanently frozen silt. If the ice melts, the resulting silt mixture resembles soup! Construction disasters can be caused by such a thaw and the resulting subsidence, or settling, of surface features. Entire megaprojects-such as the Jenpeg dam diversion in Canada-have also been affected by the unpredictable behavior of permafrost. Thermosiphons offered one solution to permafrost on the Alaska pipeline. Other options exist. To avoid settling, engineers try to build on bedrock or coarse, well-drained soil with a low ice content. Builders can also maintain stable soil by insulating structures to prevent permafrost thawing. Small, lightweight structures may need only an airspace between floor and soil surface, created by raising the building on stilts. Larger structures require the support of insulated pilings driven deep into the permafrost. This technique allowed the Russians to build entire cities on permafrost in Siberia. Permafrost's capacity to preserve plants and animals for centuries gives scientists a window into the past to help them assess how rapidly greenhouse pollutants may be warming the Earth. Ground temperatures indicate past climatic conditions and current changes in world ambient temperatures, providing an understanding of the complex interactions of human-induced global warming, ice melting, and potential sea level changes.

Activity

The speed with which ice melts in permafrost depends on how much heat and pressure are applied to it. You can demonstrate these principles with coffee cups, water, and ice. Materials
  • large, flat cake pan filled with water
  • 5 identical ceramic coffee cups with bottom rims that would make an indentation
  • hot water
  • ice water
  • sponge for insulation
  • a freezer
  1. Fill the pan with about 1" (2.5 cm) of water. Place it in a freezer, along with one of the empty cups.
  2. When the water is frozen, remove the pan and cup from the freezer.
  3. Place the empty cup on the ice.
  4. Fill another cup with ice water and place it on the ice.
  5. Fill a third cup with very hot tap water and place it on the ice. (Be sure to place all cups so that they do not touch each other.)
  6. Fill a fourth cup with heavy rocks and place it on the ice.
  7. Fill the last cup with hot tap water. Put the sponge on the ice and place the cup on top of the sponge.
  8. If possible, place the pan with the five cups back into the freezer.
  9. Every five minutes, remove the cups that originally had hot water and refill them with hot water.
  10. After 15 minutes, remove the pan from the freezer. Remove all five cups from the pan. Feel the surface of the ice. Can you tell where the empty cup sat? Can you tell which ring was created by the cup with hot water that sat directly on the ice? How does the ice look under the insulating sponge? What about the cup containing the rocks and the cup containing the ice water? Questions
    1. What construction techniques could minimize heat transfer from a building to the permafrost?

Resources

  • Bruemmer, F. (1987, Apr) Life upon the permafrost. Natural History, pp. 31-38.
  • Fodor, R.V. (1981) Frozen earth: Explaining the ice ages. Hillside, NJ: Enslow Publishers.
  • Johnston, G.H. (1981) Permafrost engineering design and construction. New York: Wiley and Sons.
  • Kurten, B. (1986) How to deep-freeze a mammoth, (chapter 9). New York: Columbia University Press.
  • Sutcliffe, A.J. (1985) On the track of ice age mammals. Cambridge, MA: Harvard University Press.
  • Additional sources of information Geophysical Institute University of Alaska/Fairbanks Fairbanks, AK 99775-0800 (907) 474-7558
  • International Permafrost Association Troy Pewe, President Arizona State University Box 871404 Tempe, AZ 85286-1404