GPR-derived archit ecture of large-scale icelandic jokuthlaup deposits, North-East Iceland

Jokulhlaups (glacial outburst floods) occur frequently throughout Iceland and across most of the glaciated regions of the world. The largest of these jokulhlaups are known to have occurred along the northern margin of the Vatnajokull Icecap and (drained down the JokulsS B Fjollum river during the Holocene. Unfortunately, little is known about the number, frequency, age and flow characteristics of the Jokulsa B Fjollum jokullhlaups and the relationship between their deposit architectures and the underlying volcanic lavas. During the summer of 2003, a total of over 20 km of GPR data was collected from a variety of jiikulhlaup outwash sediments across the Jokulhlaups flood plain. GPR results and corresponding facies interpretations are presented for the outwash deposits at two locations: Kverkfjoll, (approximately 20 Km from the jokul hlaup source) and MoBrudalur (approximately 100 Km downstream from the glacial margin). By combining the GPR data with ground surveying, photogrammetry and detailed sedimentary outcrop evidence, this study adds new perspectives to the sedimentary analysis of high-magnitude jbkulhlaup events and their large-scale bars and bedforms. The results indicate that sedimentary architectures are controlled by the topographic nature of the underling lavas and the flow conditions in each region. By analysing the GPR derived facies in detail, it is also possible to identify different phases of jokulhlaup deposition. This information is vital for the assessment of jokulhlaup magnitudes, frequencies, and pathways and can be used for the prediction of future jokulhlaup impacts.