What are tundra polygons?
Tundra polygons are what they sound like – pieces of ground that are shaped like polygons. These polygons are formed because of the freeze-thaw cycle that occurs in permafrost areas.
Permafrost is the layer of permanently frozen ground under the thaw layer of soil (called the active layer). In the Arctic, the permafrost can be found anywhere from about 10 cm to a meter under the active layer, depending on how close the area is to lakes or streams. Water being a good transmitter of heat, the ground nearby tends to thaw to slightly deeper depths.
Ok, so what does that have to do with polygons? Well, as the active layer thaws, the water cannot percolate down. So, water must either run off the surface or accumulate on the soil to form ponds or boggy areas. Freezing in the winter and thawing in the summer causes many cycles of expanding and contracting which form cracks in the ground. As these cracks form they fill with water which form ice wedges into the permafrost. This mechanical work done on the soil is somewhat organized as fracture lines form in the shapes of polygons. As the wedges grow, the soil is pushed up more and more. Some of these cracks eventually form a boundary around a lower area which fills with water. This tends to form a patchwork of low and high polygons on the landscape.
This terrain makes for difficult walking and, thus, the need for hip waders with good ankle support!
See these websites for more information on and pictures of tundra polygons:
http://www.gi.alaska.edu/ScienceForum/ASF6/690.html
http://www.bgrg.org/pages/education/alevel/coldenvirons/Lesson%2020.htm
http://www.athro.com/geo/trp/gub/tundra.html
http://www.gi.alaska.edu/ScienceForum/ASF2/257.htm
Also, see http://archive.arcus.org/TREC/VBC/index.php?showtopic=199 to try to simulate your own tundra polygons.
Leslie,
Thanks for this information. I just happened to be looking for some information on tundra polygons. You did all of the work for me.
Tom
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