Palaeohydrology and sedimentary impacts of jökulhlaups from Kverkfjöll, Iceland

Jökulhlaups (glacial outburst floods) occur frequently within Iceland and within most glaciated regions of the world. The largest jökulhlaups known to have occurred within Iceland drained from the northern margin of the Vatnajökull and along the Jökulsá á Fjöllum during the Holocene. However, little is known about the number, age and flow characteristics of the Jökulsá á Fjöllum jökulhlaups. One source of meltwater into the Jökulsá á Fjöllum is Kverkfjöll, a glaciated stratovolcano. This paper provides detailed sedimentological evidence demonstrating that jökulhlaups have routed through Kverkfjallarani and hence from Kverkfjöll. Sedimentological evidence of jökulhlaups includes valley-fill deposits and slack water deposits. Lithofacies, which are indicative of high-magnitude fluvial sedimentation, show that these deposits cannot be the result of nonjökulhlaup processes. The situation and nature of the sediments permit palaeoflow reconstructions. Fine-grained deposits within slack water deposits mark a break in jökulhlaup deposition and suggest that at least three jökulhlaups have drained through Hraundalur, the predominant valley within Kverkfjallarani. Evidence of lava overrunning ‘wet’ jökulhlaup deposits indicates that jökulhlaups occurred in close association with volcanic eruptions in the Biskupsfell fissure. The largest jökulhlaup was initially hyperconcentrated and subsequently became more fluid. Slope–area reconstructions indicate that the largest jökulhlaup had a probable average peak discharge of 45,000–50,000 m3 s−1; however, the peak discharge attenuated by 25–30% in just 25 km. These observations quantify the number, rheology, hydraulics and chronology of jökulhlaups from Kverkfjöll and hence within the Jökulsá á Fjöllum. This study presents a model of jökulhlaup impacts and characteristics from glaciated volcanoes and/or within volcanic rifting zones.
Keywords

Kverkfjöll;
Outburst floods;
Jökulhlaups;
Rheology;
Flow characteristics;
Iceland