RECONSTRUCTION OF JOKULHLAUPS ALONG THE HVITA RIVER AND GULLFOSS WATERFALL, ICELAND, DURING EARLY HOLOCENE ICE SHEET RETREAT

Glacial lake outburst floods (jökulhlaups) have occurred across Earth throughout the Quaternary, leaving a geomorphologic, sedimentological, and climatic legacy that extends far beyond the source region and can persist for millennia. 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 canyons, bedrock channels, 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 new methods to better constrain flood timing, routing, magnitude, and recurrence interval at this underexplored site. This presentation synthesizes geomorphologic field evidence, hydrologic reconstructions using HEC-RAS modelling and paleohydraulic calculations, and ongoing cosmogenic nuclide analyses to reconstruct flood dynamics and chronology. It situates the Kjölur jökulhlaups within the context of Icelandic Ice Sheet retreat and paleoenvironmental change, presenting a series of scenarios of ice margin position, glacial lake evolution, and jökulhlaup drainage. Finally, it assesses the Kjölur jökulhlaups as an analogue to past and contemporary glacial lake outburst floods in Arctic and alpine regions worldwide, where they pose an increasing risk to downstream communities due to climate-driven meltwater lake expansion.