GEOMORPHOLOGIC EVIDENCE AND TIMELINE RECONSTRUCTION OF HOLOCENE JOKULHLAUPS ALONG THE HVITA RIVER AND GULLFOSS, ICELAND

Gullfoss is one of Iceland’s most visited tourist sites, a two-tiered waterfall where the Hvítá River plunges 32 meters into the 70-m-deep Hvítárgljúfur canyon. This system is one of the most prominent lines of evidence for glacial lake outburst floods that surged across southwestern Iceland in the early Holocene. As the Icelandic Ice Sheet retreated from the central highlands, a series of ice-dammed glacial lakes pooled at the ice margin and drained in catastrophic jökulhlaups. One such lake formed in the Kjölur basin and drained south along the modern-day course of the Hvítá, leaving behind extensive erosional and depositional evidence. The largest events reached an estimated maximum peak discharge of 3 x 10⁵ m³ s^-1, ranking them among the largest known floods in Iceland and on Earth. Yet only one publication to date has focused on the Kjölur jökulhlaups (Tómasson, 1993).

This project builds on previous research by employing new methods to better constrain flood timing, magnitude, routing, and frequency. This presentation has four main goals: 1) present new and synthesized geomorphologic field evidence; 2) outline a sampling strategy for geochronological analyses, namely cosmogenic nuclide exposure dating; 3) discuss future flood reconstruction efforts such as hydraulic modeling; and 4) situate the Kjölur floods in the broader context of jökulhlaup dynamics and deglaciation chronology in Iceland. Most research on Icelandic jökulhlaups has focused on floods triggered by volcanic and geothermal activity beneath the southernmost ice caps; but the Kjölur floods, not triggered by volcanogenic processes, may provide a better analog for most global glacial outburst floods, which pose an increasing hazard due to rapid climate-driven glacial lake expansion. Furthermore, this project has excellent potential to bridge the gap between academic research and public outreach through communication to a high number of international visitors.