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. This study combines remote sensing and in situ methods to characterize transitional rock glaciers in the Carpathian Mountains. We used Persistent Scatterer Interferometry (PSInSAR) on Sentinel-1 images (2015–2020) to detect slope movements associated with rock glaciers and differential GNSS measurements (2019–2021) to track horizontal movement of 25 survey markers. Continuous ground temperature and winter snow cover bottom temperature (BTS) measurements examined energy exchange fluxes affecting these rock glaciers. Geophysical surveys (electrical resistivity tomography and refraction seismic tomography), and petrophysical joint inversion (PJI) quantified ice content in one rock glacier. PSInSAR identified 92 moving areas (MAs) with slow displacement (<5 cm yr−1) mostly between 2000 and 2300 m, where solar radiation was minimal. Near-surface thermal data from four rock glaciers suggest favourable conditions for permafrost persistence, largely driven by internal ventilation processes (e.g., advection heat fluxes) throughout the winter. BTS confirmed very low ground surface temperatures over much of the investigated rock glaciers, particularly in their upper parts and within the MAs. Geophysical investigations reveal ice-poor permafrost remnants in the Galeşu rock glacier, while PJI modelling estimated a low ground ice content (∼ 18 %) in its upper sector. At this site, surface displacements stem from active layer deformation, not permafrost creep. At two other sites, dGNSS markers moved consistently toward rock glacier fronts, indicating permafrost creep. Regarding activity status, the majority of rock glaciers in the Retezat Mountains were categorized as relict, with only 21 % classified as transitional. Transitional rock glaciers occur 150 m higher and are slightly smaller than relict ones.