Geophysical measurements of the southernmost microglacier in Europe suggest permafrost occurrence in the Pirin Mountains (Bulgaria)

Abstract. There are no large glaciers in the territory of Bulgaria, but small patches of snow
and firn have been observed in the high mountains at the end of summer. Perennial
snow patches and microglaciers are considered indicators of permafrost occurrence.
The results from the first detailed geophysical investigations of the Snezhnika
glacieret, considered to be the southernmost microglacier in Europe, situated in
the Golyam Kazan cirque, Pirin Mountains, Bulgaria, are presented in the paper.
Ground-penetrating radar (GPR) and 2D electrical resistivity tomography (ERT)
were used to estimate the thickness of the microglacier as well as its subsurface
structure. Measurements started in 2018 and continued over the next 2 years in
order to assess changes in its size and thickness. The mean thickness of Snezhnika
is about 4–6 m, reaching 8 m or probably more in some areas. ERT measurements
of the deeper parts of the microglacier beds show high electrical resistivities
reaching over 60 000 Ωm at a depth of 4–10 m. An anomaly at this depth
is likewise distinguishable on the GPR profiles. These anomalies are interpreted
as permafrost areas and were consistently observed on the ERT and GPR profiles
in the 2 years of the study. These results imply for the first time the
existence of permafrost in the Pirin Mountains and in Bulgaria.
