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

Gullfoss is one of Iceland’s most visited tourist sites, a majestic two-tiered waterfall where the Hvítá River thunders over a 32-meter drop into the Hvítárgljúfur canyon. The waterfall and canyon are some of the most obvious lines of evidence for the paleofloods that surged across the region ~9500 years BP. Over a span of 100-200 years, a series of floods drained the ice-dammed glacial lake Kjölur in the south-central Icelandic highlands. 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 (Tómasson, 1993). Geomorphologic evidence for catastrophic floods abounds along the estimated drainage routes, including cataract networks, canyons, spillways, strath terraces, boulder bars, and scoured bedrock.

Most recent research on Icelandic glacial outburst floods—known as jökulhlaups—has focused on floods generated by volcanic and geothermal activity beneath Iceland’s southernmost ice caps; yet only a few studies have examined the Hvítá floods. A pioneering study by Tómasson (1993) reconstructed these paleofloods based on geomorphologic evidence, paleolake strandlines, tephrochronology, and sedimentology. This project seeks to build on previous research by employing new methods to better constrain flood timing, magnitude, and routing. This presentation reports on initial field work in the Kjölur-Hvítá-Gullfoss region. It has three main goals: 1) to present geomorphologic field evidence along the estimated flood route, including features not reported in Tómasson’s study; 2) to outline a sampling strategy for geochronological analysis, namely sediment profiles and cosmogenic nuclide dating of bedrock surfaces; and 3) to situate the Hvítá jökulhlaups in the broader context of catastrophic flood geomorphology in Iceland, with specific comparison to the Jökulsá á Fjöllum river channel and Jökulsárgljúfur canyon, which exhibit many similar features. This research will yield insight into ice-dammed proglacial lake drainage dynamics, an increasingly important field in light of rapid climate-induced glacial lake expansion worldwide. It also has excellent potential to bridge the gap between academic research and public outreach since results could be communicated to such a high number of international visitors.