Future proglacial lake evolution and outburst flood hazards in south Iceland

Arctic regions are warming at more than double the global average rate, causing significant changes in cryospheric and hydrologic patterns. As glaciers retreat, meltwater can accumulate in expanding proglacial lakes, which often form in overdeepened basins with large storage capacities and steep valley walls that are prone to paraglacial slope failures. If a mass movement event such as a rockfall or landslide enters the lake, the water can drain in a glacial outburst flood, significantly modifying the landscape. Moreover, many lakes are upstream of infrastructure, communities, and tourism sites, resulting in a high potential societal impact in the event of a flood. This process is a well-documented trigger of floods in glacial regions across the world, but it remains an emerging and understudied hazard in Iceland.This study investigates past and future proglacial lake evolution and evaluates mass movement-triggered outburst flood risk at two sites in south Iceland. We present: 1) updated maps of lake bathymetry and subglacial topography derived from multibeam sonar and radio-echo sounding surveys, respectively; 2) past lake volume changes and projected future lake extent and volume; and 3) potential slope failure source areas and scenarios of mass movement-triggered outburst floods. These results lay the foundation for future work on flood modeling and hazard planning to mitigate impacts on communities and infrastructure. This project also serves as an excellent pilot study for this emerging hazard in Iceland and has significant potential for application to proglacial lakes in other Arctic and alpine regions.