The Aneto glacier's (Central Pyrenees) evolution from 1981 to 2022: ice loss observed from historic aerial image photogrammetry and remote sensing techniques

The Aneto glacier, although it may be considered a very small glacier (<0.5 km2), is the largest glacier in the Pyrenees. Its surface and thickness loss have been continuous in recent decades, and there have been signs of accelerated melting in recent years. In this study, thickness and surface losses of the Aneto glacier from 1981 to 2022 are investigated using historical aerial imagery, airborne lidar point clouds and unoccupied aerial vehicle (UAV) imagery. A ground-penetrating radar (GPR) survey conducted in 2020, combined with data from photogrammetric analyses, allowed us to reconstruct the current ice thickness and also the existing ice distribution in 1981 and 2011. Over the last 41 years, the total glacierised area has decreased by 64.7 %, and the ice thickness has decreased, on average, by 30.5 m. The mean remaining ice thickness in autumn 2022 was 11.9 m, as against the mean thickness of 32.9, 19.2 and 15.0 m reconstructed for 1981 and 2011 and observed in 2020, respectively. The results demonstrate the critical situation of the glacier, with an imminent segmentation into two smaller ice bodies and no evidence of an accumulation zone. We also found that the occurrence of an extremely hot and dry year, as observed in the 2021–2022 season, leads to a drastic degradation of the glacier, posing a high risk to the persistence of the Aneto glacier, a situation that could extend to the rest of the Pyrenean glaciers in a relatively short time.

This work was supported by the InterregPOCTEFA project OPCC ADAPYR and Spanish Ministry of Economy and Competitiveness project (project no. CGL2017-82216-R), and the Spanish Ministry of Science and Innovation (grant nos. PID2020-113247RB-C21 and PID2021-124220ob100/MARGISNOW). Jesús Revuelto has been supported by the projects Juan de la Cierva I (project no. IJC2018-036260-I) and Ramón y Cajal (project no. RYC2021-033859-I). Ixeia Vidaller is enrolled in the PhD programme at the University of Zaragoza (grant no. FPU18/04978). Eñaut Izagirre is supported by the UPV/EHU (grant no. PPGI19/02) and the Consolidated Research Group IT1678-22 (Basque Country Government). Esteban AlonsoGonzález has been funded by the CNES postdoctoral fellowship.

We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

Peer reviewed