Monitoring high resolution variations in proglacial lake area using an Uncrewed Aerial Vehicle (UAV) at Fjallsjökull, Iceland

The subglacial hydrological system is a key component in understanding the response of glaciers to climate change. However, due to its inaccessibility, the subglacial system is logistically difficult to investigate. Here we use an Uncrewed Aerial Vehicle (UAV) to monitor variations in the lake area of Fjallsárlón, a large proglacial lake in SE Iceland, at high spatial and temporal resolutions to better understand the hydrology of the adjacent soft-bedded outlet glacier Fjallsjökull. Surveys were undertaken over 10 days in July and 7 days in September 2023, with the acquired imagery used to generate high-resolution orthomosaics and DEMs (0.01 m and 0.03 m, respectively). We then developed and applied a novel method to the resultant 3D models to measure variations in proglacial lake area on a diurnal scale, bridging the gap between ground and satellite-based observations. We were able to measure a minimum diurnal variation of ~9,800 m2 and a maximum diurnal variation of ~56,000 m2 in lake area during the study period. As such, our results indicate the potential of UAVs to monitor changes in proglacial lake area at high resolutions. We suggest that the novel method applied here can successfully be used to measure variations in the lake area of Fjallsárlón, which can be used alone or alongside satellite records of lake area change. From these data, insights into the outputs of the hydrological system can be obtained, which can be used alongside meteorological data to better understand the subglacial system of Fjallsjökull.