Cold soil in the groove

Soil polygons in the Tundra. Photo by Sebastian Zubrzycki. Click to see the original image at Imaggeo.

Often, soils from cold regions, such as Arctic soils, show polygonal forms in their surface. These polygons are formed because of the freeze-thaw cycle, characteristic of permafrost.

What is permafrost?

Permafrost is a subsurface soil layer which stays permanently frozen (below 0 ^oC) during long periods of time, usually more than two consecutive years.

Circum-Arctic Map of Permafrost and Ground Ice Conditions. Credit: J. Brown, O.J. Ferrians Jr., J.A. Heginbottom and E.S. Melnikov. Click to see the original image at Wikimedia Commons.

Most extensive permafrost areas can be found in circumpolar areas from North America (Canada and Alaska), Asia (Siberia), Europe (Norwich), cold continental areas (Tibet) and some islands (South Georgia and the Sandwich Islands, in the Atlantic Ocean). And on Mars!

Phoenix landing-day image near north pole of Mars showing flat terrain, containing what appears to be a polygonal pattern, stretching from the foreground to the horizon. Credit: NASA/Jet Propulsion Lab/University of Arizona. Click to see the original image at Wikimedia Commons.

The soil layer above the permafrost (known as the active layer) is the part of soil that thaws during the warm season and freezes again at the beginning of the cold season, because the influence of air temperature is greater in the first centimeters of soil. Commonly, the thickness of the active layer may vary between 10 and 100 cm depending on the season, aspect, vegetation, soil texture and proximity to water bodies.

Permafrost landscape. Photo by Reinhard Pienitz. Click to see the original image at Imaggeo.

How do polygons form?

Cryoturbation is one of the main processes in the soil active layer. As a consequence, the soil surface in these cold areas often show polygons, circles, steps and stripes formed by stones and fine sediments.

Stone rings on Spitsbergen. Photo by Hannes Grobe. Click to see the original image at Wikimedia Commons.

Repeated groundwater freezing/thawing cycles causes contraction/expansion of soil material, that forces the displacement of coarse gravels and stones over the soil surface. Areas with fine sediments (with low porosity) show larger water contents than those areas where coarse fragments accumulate.

Polygon ponds in Arctic tundra soils. Photo by Reinhard Pienitz. Click to see the original image at Imaggeo.

As a result, water-saturated, finely-textured soil expands and contracts more easily during freezing/thawing cycles than coarsely textured stony areas. In the long term, stone polygons and other patterns may appear on the soil surface. Fine sediments in the center of polygons usually form ponds and small bogs.

Thawing permafrost in Siberia. Photo by Guido Grosse. Click to see the original image at Imaggeo.

Know more

Christensen, P.R. 2006. Water at the poles and in permafrost regions of Mars. Elements 2, 151-155. DOI: 10.2113/gselements.2.3.151.

Dobinski, W. 2011. Permafrost. Earth-Science Reviews 108, 158-169. DOI: 10.1016/j.earscirev.2011.06.007.

Gruber, S. 2012. Derivation and analysis of a high-resolution estimate of global permafrost zonation. The Cryosphere 6, 221-233. DOI: 10.5194/tc-6-221-2012.

Guglielmin, M. 2012. Advances in permafrost and periglacial research in Antarctica: A review. Geomorphology 155-156, 1-6. DOI: 10.1016/j.geomorph.2011.12.008.

Haeberli, W. 2013. Mountain permafrost – research frontiers and a special long-term challenge. Cold Regions Science and Technology 96, 71-76. DOI: 10.1016/j.coldregions.2013.02.004.

Haeberli, W., Noetzli, J., Arenson, L.b Delaloye, R., Gärtner-Roer, I., Gruber, S., Isaksen, K., Kneisel, C., Krautblatter, M., Phillips, M. 2011. Mountain permafrost: Development and challenges of a young research field. Journal of Glaciology 56, 1043-1058. DOI: 10.3189/002214311796406121.

Langer, M., Westermann, S., Muster, S., Piel, K., Boike, J. 2011. The surface energy balance of a polygonal tundra site in northern Siberia – Part 1: Spring to fall. The Cryosphere 5, 67, 79. DOI: 10.5194/tc-5-151-2011.

Langer, M., Westermann, S., Muster, S., Piel, K., Boike, J. 2011. The surface energy balance of a polygonal tundra site in northern Siberia – Part 2: Winter. The Cryosphere 5, 509-524. DOI: 10.5194/tc-5-509-2011.

Lin, Z.H., Zhang, Y.H. 2013. The general review of permafrost temperature research methods. Applied Mechanics and Materials 405-408, 158-161. DOI: 10.4028/www.scientific.net/AMM.405-408.158.

McClymont, A.F., Hayashi, M., Bentley, L.R., Christensen, B.S. 2013. Geophysical imaging and thermal modeling of subsurface morphology and thaw evolution of discontinuous permafrost. Journal of Geophysical Research F: Earth Surface 118, 1826-1837. DOI: 10.1002/jgrf.20114.

Wade F.A., De Wys, J.N. 1968. Permafrost features on the martian surface. Icarus 9, 175-185. DOI: 10.1016/0019-1035(68)90011-0.

Xie, s., Qu, J., Zu, R., Zhang, K., Han, Q., Niu, Q. 2013. Effect of sandy sediments produced by the mechanical control of sand deposition on the thermal regime of underlying permafrost along the Qinghai-Tibet railway: Land Degradation and Development 25, 453-462. DOI: 10.1002/ldr.1141.

Zhao, L., Jin, H. , Li, C., Cui, Z., Chang, X., Marchenko, S.S., Vandenberghe, J., Zhang, T., Luo, D., Guo, D., Liu, G., Yi, C. 2013. The extent of permafrost in China during the local Last Glacial Maximum (LLGM). Boreas. In press. DOI: 10.1111/bor.12049.

This post was also published simultaneously in G-Soil.