Slide 17: Thermal indicators: permafrost
Permafrost is a term used to describe a condition whereby the water in the soil is frozen all year round. The depth of permafrost may differ, but it generally thaws up metre in depth in summer periods. About 25% of the Northern Hemisphere landmass is under permafrost , including much of Canada, China, Russia and Alaska (Brown et al., 1997).
Significant portions of this area are now undergoing melting as a result of raised temperatures.
This is seen through the sudden appearance of potholes of considerable size and the draining of many lakes as their frozen base is removed.
However, direct measurement of the melting of permafrost has been gathered over the last twenty years in many regions of the world (Gravis et al., 1988; Weller and Anderson, 1998; Romanovsky and Osterkamp, 1999)
Onset, magnitude and extent of permafrost melting varies from area to area.
Brown, J., O.J. Ferrians, Jr., J.A. Heginbottom and E.S. Melnikov, 1997: Circum-Arctic map of permafrost and ground-ice conditions. U.S. Geological Survey Circum-Pacific Map CP- 45, 1:10,000,000, Reston, Virginia.
Gravis, G.F., N.G. Moskalenko and A.V. Pavlov, 1988: Perennial changes in natural complexes of the cryolithozone. In: Proceedings of the Fifth International Conference on Permafrost, Trondheim, Norway, vol. 1, 165-169.
Osterkamp, T.E. and V.E. Romanovsky, 1999: Evidence for warming and thawing of discontinuous permafrost in Alaska. Permafrost and
Periglacial Processes, 10(1), 17-37.
Weller, G. and P.A. Anderson (eds.), 1998: Implications of Global Change in Alaska and the Bering Sea Region. Proceedings of a Workshop, June 1997, Centre for Global Change and Arctic System Research, University of Alaska Fairbanks, Fairbanks, Alaska, 157 pp.