Future proglacial lake evolution and outburst flood hazard in south Iceland

Abstract

Arctic regions are warming at more than double the global average rate with significant impacts on glaciers and hydrologic systems. Iceland is on the front line of this rapid climate change, with a predicted loss of ~20% of its current ice cap volume by 2100. Much of this meltwater is stored in proglacial lakes at outlet glaciers, which are at risk of draining in glacial lake outburst floods (GLOFs). Most contemporary outburst floods in Iceland have been triggered by subglacial eruptions and geothermal activity; however, GLOFs resulting from mass movement events into lakes are an emerging—yet understudied—hazard. Many of Iceland’s proglacial lakes form in overdeepened basins, storing large volumes of meltwater; expanding lake extent creates more surface area for mass movements to enter; and retreating glaciers remove support from valley walls, increasing rockfall and landslide risk. Several large rockfalls have fallen onto glaciers in the past decades; however, these events may enter lakes as glacier retreat progresses and lakes expand.We investigate this emerging hazard by predicting proglacial lake evolution and assessing GLOF risk under a future warming climate at three sites in south Iceland. This presentation focuses on the proglacial lake at Fjallsjökull, an outlet glacier of the Vatnajökull ice cap. We present lake volume changes since 1980, derived from bathymetric surveys and mapped lake surface areas. We then estimate future lake volume and extent changes from the present until 2100 based on: 1) local topography derived from bathymetric mapping, ArcticDEM, and subglacial topography from radio-echo sounding surveys; and 2) projected glacier retreat under different climate warming scenarios. Next, we identify potential hazards from mass movement events entering the lake at its current and future extents based on field mapping and remote sensing imagery. Finally, we discuss implications of a glacial outburst flood on downstream communities, infrastructure, and tourism, laying the foundation for future work on hazard assessment and flood modeling. This site is an excellent pilot study for this emerging hazard in Iceland and has significant potential for application to other Icelandic and Arctic glacial lakes.