Mapping and quantification of proglacial landscape changes based on time-series of UAV surveys: A case study of a temperate glacial landsystem of Fjallsjökull/Hrútárjökull, SE Iceland

Modern glaciers and processes operating within their foreland are often used as analogues to infer past glacial conditions and interpret dating results. As such, an important research question is how glacial landforms changed over time after being created by ice or released from under the ice, and how confident can we use them as modern analogues of past environments? Proglacial areas exposed because of glacier recession are among the most dynamic landscapes in polar and mountainous regions and are intensively modified by various geomorphological processes associated with ice margin retreat, meltwater activity, and paraglacial adjustment of topography. As these areas contain important traces of the former glacial regime and dynamics, quantification of the recent transformation of these areas is crucial in terms of glacial landsystem studies.

In this study, we quantified recent landscape dynamics in proglacial areas of Fjallsjökull and Hrútárjökull (SE Iceland) based on time series of unmanned aerial vehicle surveys (UAV) from 2014, 2016, 2017, 2018, 2019 and 2021. UAV data were processed using the structure from motion (SfM) approach to generate detailed (0.1 m ground sampling distance) orthomosaics and digital elevation models. Based on the results of geomorphic change detection, five types of landscape dynamics were identified: (1) Degradation of ice-cored moraines and expansion of the lake; (2) Ice margin retreat and melting; (3) Ice margin oscillation and dislocation of the esker; (4) Degradation of buried snout and development of pitted outwash; (5) Degradation of buried ice in the overdeepening. In general, the volume balance for Fjallsjökull/Hrútárjökull foreland over the 2014-2021 period was negative. Large-scale changes were related to the retreat of the glaciers’ margin, ice melting and drainage reconfiguration. A similar magnitude of volume loss was observed in places where the ice-cored moraines degraded, and the lake expanded. Degradation of buried ice and associated collapsing of outwash plain was responsible for minor volume loss. In some relatively small areas, gain in elevation was observed – it was primarily associated with ice margin pushing or transporting sediments during winter re-advances and, to a much lesser degree, by mobilizations of sediments due to debris flows. Relatively large areas of glacial foreland remained stable over the observation period. However, as an example of collapsing outwash indicates, topography adjustment due to the final melting of dead ice might occur several tens of years after the ice margin apparently retreated, and the ground was stabilized and vegetated.

This research was funded by National Science Centre, Poland, project number 2019/35/B/ST10/03928.