Glacial lake outburst floods (jökulhlaups) have occurred throughout the Quaternary in glaciated regions worldwide. Reconstructing flood chronology yields insight into deglaciation processes, environmental change and the role of extreme events in landscape evolution. As the Icelandic Ice Sheet (IIS) retreated across Iceland in the Early Holocene, large‐scale jökulhlaups drained from ice‐dammed glacial lakes. Extensive geomorphological evidence exists along the modern‐day course of the Hvítá River in southwestern Iceland for floods from Glacial Lake Kjölur in the central highlands. Existing palaeoenvironmental records indicate flood drainage during the final phase of IIS retreat, but chronology is poorly constrained. This study reports Chlorine‐36 cosmogenic nuclide exposure ages of seven bedrock surfaces along this flood route, marking the first time this method has been used to date Hvítá jökulhlaup evidence. Results yield four clustered ages that indicate flood drainage between 9.2 and 10.0±1.0 ka. When interpreted alongside geomorphological evidence and hypothesized ice sheet dynamics, this suggests either a single flood or multiple floods with decreasing sizes, indicating rapid ice sheet retreat. These results may also suggest that ice persisted in the region up to ~1 ka later than previous records show; however, this could be due to the ~1 ka uncertainty range in exposure ages. This pioneering application of exposure dating of the Hvítá floods yields insight into IIS deglaciation dynamics, flood landscape modification and hydrological response to glacier retreat in a warming climate, serving as a potential analogue to contemporary and future ice sheets worldwide. It also illustrates the complexity and challenge of integrating different types of palaeoenvironmental records to reconstruct landscape evolution and lays a foundation for additional exposure dating of flood and glacial evidence in Iceland.
Wells et al. (Tue,) studied this question.