Slow-moving rock glaciers in marginal periglacial environment of Southern Carpathians

Abstract. Rock glaciers, composed of debris and ice, are widely distributed across cold mountain regions worldwide. Although research on rock glaciers is gaining momentum, the distinct behaviour of rock glaciers in the marginal periglacial environments remains poorly understood. In this study, we combine remote sensing and in situ methods to gain insights into the characteristics of transitional rock glaciers in the Carpathian Mountains. We applied Persistent Scatterer Interferometry (PSInSAR) to Sentinel-1 images from 2015 to 2020 to identify areas with slope movements associated with rock glaciers and differential GNSS measurements (2019–2021) to detect the horizontal movement of 25 survey markers. Continuous ground temperature monitoring and measurements of the bottom temperature of the winter snow cover were used to examine the energy exchange fluxes characteristics of transitional rock glaciers in the Carpathians. The subsurface of one transitional rock glacier was investigated using geophysical measurements (electrical resistivity tomography and refraction seismic tomography), while petrophysical joint inversion was used to quantify the ice content. The PSInSAR methodology identified 110 moving areas (MAs) with low displacement rates (< 5 cm yr^-1). These MAs are generally located between 2000 and 2300 meters where solar radiation is minimal. Late winter ground surface temperature data from slow-moving rock glaciers point to permafrost conditions. Geophysical investigations reveal remnants of ice-rich permafrost within the Galeșu rock glacier, while petrophysical joint inversion modelling indicates a low ground ice content (~ 20 %) in its upper sector. The slow surface movement of rock glaciers in the marginal periglacial mountains is driven by the deformation of thin, frozen layers. Regarding activity status, the majority of rock glaciers in the Retezat Mountains are categorized as relict, with only 21 % classified as transitional. The results of our study emphasize the benefit of combining Sentinel-1 SAR data with comprehensive field investigations, particularly in regions with slow-moving rock glaciers.