Assessing rock glaciers for their hydrological significance in the Semi-arid Andes, Chile

Abstract

Rock glacier plays an important hydrological role in the semi-arid Chilean Andes, acting as buffers against water scarcity in a warming climate. This role will become more significant in the future since the glaciers in the region lose mass at a faster rate. Quantifying the surface velocity of rock glaciers is the first step in assessing their ice content, since high ice content is a prerequisite for rock glacier creep. In this study, multi temporal Interferometric Synthetic Aperture Radar (InSAR) is used to quantify surface velocities for 115 rock glaciers between 2016 and 2023 in the Coquimbo region in the semi-arid Chilean Andes (30-31°S). In addition, the displacement time-series is investigated for The Northen lobe of the Tapado rock glacier, Llano Des Las Libres and one unnamed rock glacier. The open-source software, EZ-InSAR, was used for the processing with a small baseline subset (SBAS) approach to obtain displacement time series. To ensure reliable results, the processing parameters were tested on a small subset on a short timescale before applying the most suitable parameters to quantify the velocities in Coquimbo from 2016 to 2023. The mean annual surface velocities of the 115 rock glaciers between 2016 and 2023 in the Coquimbo spans from 2.2 to ~10 cm/year. Rates which are underestimated due to long temporal baseline in the network of interferograms during the austral winter. The time-series revealed a general acceleration of Tapado rock glacier, with rates accelerating from ~15 cm/year in 2017/2019 to ~91 cm/year in 2020/2021. Llano Des Las Liebres had rates of ~40 cm/year in 2017/2019 to 190 cm/year in 2020/2021. InSAR has the potential to quantify multi annual rock glacier velocities on a regional scale and for detection of annual variations in surface velocities. Some improvements in the use of InSAR have been identified that may remove ambiguities in the interpretation of InSAR data and make the characterization of rock glacier velocities more robust.