Geomorphologic and Geochronological Reconstruction of Holocene Jökulhlaups along the Hvítá River and Gullfoss Waterfall, Iceland

Authors: Greta Wells*, University of Texas - Austin, Sheryl Luzzadder-Beach, University of Texas at Austin, Timothy Beach, University of Texas at Austin
Topics: Geomorphology, Paleoenvironmental Change, Cryosphere
Keywords: Glacial lake outburst floods, jökulhlaups, glacial geomorphology, Iceland, paleofloods, paleoenvironmental change
Session Type: Paper
Day: 4/4/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Coolidge, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Gullfoss is one of Iceland’s most visited sites, a two-tiered waterfall where the Hvítá River plunges 32 meters into the 70-meter-deep Hvítárgljúfur canyon. This system was carved by catastrophic glacial outburst floods that surged across southwestern Iceland in the early Holocene. As the Icelandic Ice Sheet retreated, meltwater pooled at ice margins and drained in glacial lake outburst floods (GLOFs), also known as jökulhlaups. One such lake formed in the Kjölur basin and drained south from the interior highlands to the Atlantic Ocean, leaving extensive geomorphologic evidence along the modern-day course of the Hvítá. The largest events reached an estimated maximum peak discharge of 300,000 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). My project employs new methods to better constrain flood timing, magnitude, routing, and frequency. This presentation has three main goals: 1) present new and synthesized geomorphologic field evidence; 2) outline a sampling strategy for geochronological analyses, namely cosmogenic nuclide dating and tephrochronology; and 3) discuss future flood reconstruction efforts such as hydraulic modeling. Reconstructing the Kjölur floods will yield insight into Icelandic Holocene deglaciation chronology. Furthermore, most research on Icelandic jökulhlaups has focused on floods triggered by volcanic and geothermal activity beneath the southernmost ice caps; but the Kjölur floods may provide a better analogue for most global GLOFs, which pose an increasing hazard in Arctic and alpine regions worldwide due to rapid climate-driven glacial lake expansion.

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