Glacial lake development and outburst flood hazard at Sólheimajökull glacier, Iceland

Glacier retreat is projected to continue with future climate warming, expanding proglacial lakes and increasing the risk of mass movement events such as landslides or rock falls. If a mass movement enters a lake, it may generate a displacement wave or glacial lake outburst flood (GLOF), which can significantly modify landscapes and threaten communities and infrastructure downstream.

Mass movement-triggered GLOFs pose an emerging yet understudied hazard in Iceland. One such site is Sólheimajökull, an outlet glacier of the Mýrdalsjökull ice cap in south Iceland that is one of the country’s most visited spots for glacier hikes and lake tours. This study presents results from new field surveys of lake bathymetry and subglacial topography to: 1) report lake volume evolution from 2009 to 2023; 2) project future lake development scenarios under continued glacier retreat; and 3) identify areas with high topographic potential of sourcing mass movements that could trigger a GLOF.

Sólheimajökull’s proglacial lake has grown significantly since it began to form around 2007, covering ~0.45 km² by 2023. If the glacier terminus continues to retreat, the lake will expand into an overdeepened trough, roughly doubling its maximum depth, quadrupling its surface area, and increasing its volume by a factor of nine. If recent retreat rates continue, Sólheimajökull’s terminus could enter the deepest part of the trough in approximately a decade and retreat out of the lake basin within a century, though this could occur more quickly if calving rates increase due to deeper water. The estimated maximum lake extent will reach ~4 km up-valley from its current location, extending beneath several zones of the valley walls with high topographic potential of sourcing a rock fall or avalanche that could trigger a GLOF. This has significant implications for future glacier access, tourism planning, infrastructure development, and visitor risk exposure. These results can inform hazard mitigation strategies at Sólheimajökull, as well as guide studies of this emerging hazard at other proglacial lakes in Iceland.