Geomorphology, hydrology, and chronology of Early Holocene jökulhlaups along the Hvítá River and Gullfoss waterfall, Iceland

Glacial outburst floods (jökulhlaups) have occurred across Earth throughout the Quaternary, often leaving a geomorphologic, sedimentological, and climatic legacy that extends far beyond the source region and can persist for millennia. Furthermore, they pose an increasing geohazard in glaciated landscapes worldwide due to climate-driven ice retreat. Iceland experiences more frequent jökulhlaups than nearly anywhere on Earth, though most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, abundant evidence also exists for non-volcanogenic floods from proglacial lakes, which may serve as a better analogue for most global jökulhlaups.

As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater lakes formed at ice margins and periodically drained in jökulhlaups. Some of the most catastrophic floods drained from ice-dammed Glacial Lake Kjölur, surging across southwestern Iceland from the interior highlands to the Atlantic Ocean. These floods left extensive geomorphologic evidence along the modern-day course of the Hvítá River, including canyon systems, scoured bedrock, boulder deposits, and Gullfoss—Iceland’s most famous waterfall. The largest events reached an estimated peak discharge on the order of 10⁵ m³ s^-1, ranking them among the largest known floods in Iceland and on Earth. Yet, all our evidence for the Kjölur jökulhlaups comes from only one publication from a quarter-century ago.

This project employs a combination of field, modelling, and laboratory methods to better constrain flood timing and dynamics at this underexplored site. This talk synthesizes geomorphologic field mapping, HEC-RAS hydraulic simulations and paleohydraulic calculations, and cosmogenic nuclide exposure dates to reconstruct Kjölur jökulhlaup routing, hydrology, and chronology. It situates these events within the context of Pleistocene-Holocene Icelandic Ice Sheet retreat and paleoenvironmental change, presenting a series of scenarios of ice margin position, glacial lake extent, and jökulhlaup drainage. Finally, it assesses the Kjölur jökulhlaups as an analogue to contemporary glacial outburst floods in other Arctic and alpine regions in terms of flood frequency, dynamics, and landscape impact.