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Keywords:

  • discontinuous permafrost;
  • palsas;
  • electrical resistivity tomography;
  • ground ice content;
  • thermal regime;
  • climatic change;
  • mountain permafrost;
  • permafrost geophysics

ABSTRACT

Warm permafrost conditions (mean temperatures of −3°C to −0.1°C) were investigated in detail at 13 valley and mountain sites in the sporadic (10–50%) and extensive (50–90%) discontinuous permafrost zones in the southern half of the Yukon (60°N to 64°N), using a combination of ground temperature monitoring, electrical resistivity tomography (ERT), frost table probing and coring. Sites were selected to cover a wide range of substrates, vegetation types and ground ice contents. ERT profiling in the spring imaged both deep seasonal frost and perennially frozen ground. Deep active layers measured by probing at the end of summer were also detectable by ERT. Where ground temperatures indicated that the base of permafrost was at a depth of less than 25 m, vertical transitions in apparent resistivity were more sharply defined in coarse materials than in fine-grained deposits, probably because of differences in unfrozen moisture contents at temperatures just below 0°C. Apparent resistivity values related to excess ice fraction and ground temperatures were similar to those previously obtained in Mongolia and Iceland, but generally lower than in ice-rich rock glaciers in European studies. The observations revealed the complexity of site conditions where permafrost is discontinuous and the utility of ERT, in combination with other methods, to investigate permafrost thickness, spatial extent and ice content for infrastructure planning or climate change studies. Copyright © 2011 John Wiley & Sons, Ltd.