Geomorphological evidence for jökulhlaups from Kverkfjöll volcano, Iceland

Jökulhlaups (glacial outburst floods) are known to have drained along the Jökulsá á Fjöllum river in Iceland during the Holocene. However, little is known about their number, age, source, and flow characteristics. This paper provides detailed geomorphological evidence for jökulhlaups that have routed from the Kverkfjöll ice margin and hence into the Jökulsá á Fjöllum. Erosional evidence of jökulhlaups from Kverkfjöll includes gorges, cataracts, spillways, subaerial lava steps, and valley-wide scoured surfaces. Depositional evidence includes wash limits, boulder bars, cataract-fill mounds, terraces, slackwater deposits, and outwash fans. Some of these landforms have been documented previously in association with jökulhlaups. However, subaerial lava surfaces that have been scoured of the upper clinker, gorges within pillow–hyaloclastite ridges, gorges between pillow–hyaloclastite ridges and subaerial lava flows, subaerial lava lobe steps, cataract-fill mounds, and boulder run-ups are previously undocumented in the literature. These landforms may therefore be diagnostic of jökulhlaups within an active volcanic rifting landscape. The nature and spatial distribution of these landforms and their stratigraphic association with other landforms suggest that there have been at least two jökulhlaups through Kverkfjallarani. The Biskupsfell eruption occurred between these two jökulhlaups. Kverkfjallarani jökulhlaups were very strongly influenced by topography, geology, and interevent processes that together determined the quantity and nature of sediment availability. Such controls have resulted in jökulhlaups that were probably fluidal, turbulent, and supercritical over large areas of the anastomosing channel bed. Kverkfjallarani jökulhlaups would have had highly variable hydraulic properties, both spatially and temporally. The knowledge of flow characteristics that can be gained from jökulhlaup impacts has implications for recognising jökulhlaups in the rock record and for hazard analysis and mitigation within similar landscapes and upon other glaciated volcanoes.
Keywords

Kverkfjöll;
Jökulhlaups;
Outburst flood;
Geomorphology;
Volcanic rifting zone;
Iceland