Inventory of rock glaciers and protalus lobes in the Upper Noguera Pallaresa Basin (Central-Southern Pyrenees): spatial distribution, chronology, and activity

Permafrost is a key component of postglacial landscape dynamics in the highest mountains of the Pyrenees. The current high mountain landscape features a variety of landforms associated with permafrost, such as rock glaciers and protalus lobes. In this study, we present the first inventory of permafrost-related features in the upper basin of the Noguera Pallaresa River in the central-Southern Pyrenees. For the identification, mapping, and classification of these landforms, we used high-resolution cartographic data, 0.25 m/pixel air-orthophotos, 3D imagery from Google Earth, and a 2 × 2 m digital terrain model derived from airborne laser scanning (LiDAR), complemented by fieldwork. A total of 230 rock glaciers and 130 protalus lobes were identified across 11 massifs at elevations ranging from 1605 to 2813 m, covering a total area of 10.3 km 2 . Up to 68% of the rock glaciers are located at 2300–2700 m. Protalus lobes are generally found at slightly higher elevations, with 75% located between 2300 and 2700 m. Although rock glaciers occur across all lithologies, they are predominantly concentrated on granitic substrates. Genetically, 70% of the rock glaciers—and all protalus lobes—are interpreted as probably cryogenic in origin (talus-derived). In contrast, the remaining 30% of rock glaciers are thought to be glacigenic (debris-derived). Based on InSAR and geomorphological criteria, 39 active rock glaciers (17%) were identified as transitional forms with displacement velocities of 1–3 cm/year and mean front elevations of 2459 m, about 500 m below the current 0 °C MAAT isotherm in the Pyrenees (~ 2950 m). This inventory offers new insights into permafrost distribution, deepening our understanding of postglacial landscape evolution and supporting the recognition and preservation of the Pyrenees’ natural heritage.