Assessment of permafrost conditions in the highest mountains of the Balkan Peninsula

Abstract

The proposed research addresses the problem of permafrost occurrence for the first time in the highest mountains of the Balkan Peninsula. The likely/unlikely presence of ice-rich permafrost in 13 rock glaciers in the Rila and Pirin Mountains was investigated using thermal measurements (e.g., ground surface temperature monitoring, measurements of the bottom temperature of snow cover and late summer alpine spring water temperature measurements) and ground penetrating radar surveys. Based on the thermal records, intact rock glaciers appear likely above 2450 m on north-facing slopes, where incoming solar radiation is small and the pronounced shadow effect of the ridges allow an extended duration of snow cover. Thermal results revealed that the coarse blocks influence the near-surface energy exchange fluxes, confirming the significant influence of the cooling effect of high-porosity unconsolidated debris deposits. The intense ground overcooling during the early winter is mainly the result of temperature-driven air convection, whereas in late winter, the low thermal conductivity of the porous boulder mantle below a thick snow cover can cause ground cooling. Furthermore, the reduced insolation below the late-lying snow patches prevents the ground from heating up during the warm season. At most of the sites, the winter equilibrium temperatures are lower than −3 °C and the mean annual ground surface temperatures are negative or close to 0 °C. Ground penetrating radar (GPR) measurements detected permafrost occurrence in three rock glaciers underneath a thick active layer (4–10 m). Forthcoming research on this topic is needed to evaluate more carefully the importance of local conditions for permafrost preservation.