Geophysical surveys designed to delineate the altitudinal limit of mountain permafrost:: An example from Jotunheimen, Norway

Three geophysical methods have been applied to delineate the altitudinal limit of permafrost at Juvvasshoe/Jotunheimen in southern Norway. By using each method in a complementary way according to its applicability, the permafrost distribution could be analysed on both large and small scales. In addition, temperature-based methods such as the BTS method (bottom temperature of snow cover) were used to validate the results. On a large scale, electromagnetic induction profiling with the EM-31 was used to detect the location of the transition area between frozen and unfrozen ground. Within this area direct-current (DC) resistivity and refraction seismic tomography were also applied to further characterize and visualize the permafrost transition. The large scale surveys revealed a sharp increase in conductivity, indicating an increase in unfrozen water content, near 1400m a.s.l., with a possible transition zone between 1500m a.s.l. and 1380m a.s.l. The small scale investigation delineated the altitudinal limit of permafrost between 1470m a.s.l. and 1410m a.s.l., with sporadic ground ice occurrences and temperatures near the freezing point. Copyright (C) 2004 John Wiley Sons, Ltd.