Characteristics and impacts of joÌˆkulhlaups (glacial outburst floods) from KverkfjoÌˆll, Iceland
Jökulhlaups, or glacier outburst floods, have occurred during the Holocene from the
northern margin of the Vatnajökull ice cap, Iceland. Relatively little is known about the
origin, magnitude and frequency of these jökulhlaups. The volcanic rifting zone of
northern Iceland provides a new environment in which to examine jökulhlaups. Jökulhlaup
reconstructions have to date omitted 2D hydrodynamic modelling techniques. This
research therefore reconstructs jökulhlaups from Kverkfjöll volcano, a discrete source of
meltwater from northern Vatnajökull.
This research describes a suite of erosional and depositional landforms that distinguish
Kverkfjöll jökulhlaup routeways. Some of these; clinker-scoured lava, gorges with walls of
pillow and subaerial lava, lava steps, cataract-fill mounds and imbricated boulder clusters
and run-ups, are previously undocumented jökulhlaup impacts. These landforms may be
diagnostic of volcanic and/or rifting landscape jökulhlaups. Cross-cutting relationships and
sedimentary stratigraphy suggest at least three Holocene jökulhlaups from Kverkfjöll.
Kverkfjöll jökulhlaups were reconstructed using palaeocompetence, slope-area and 2D
hydrodynamic modelling. Jökulhlaups were volcanically triggered, had linearly-rising
hydrographs and peak discharges of 50,000-100,000 m3s-1, which attenuated by ~75%
within 25km. Flows were highly varied spatially and temporally, and strongly controlled
by topography, geology and sediment supply. Frontal flow velocities were ~2ms-1 but as
stage increased, mean velocities reached 5-15ms-1. Shear stress and stream power reached
1x104 Nm-2 and 1x105 Wm-2 respectively. Flows were initially hyperconcentrated and
subsequently more fluidal, supercritical and highly turbulent.
Kverkfjöll jökulhlaups achieved geomorphic work comparable to that generated by the
largest known terrestrial floods. Landscaping resulted from topographic confinement, steep
channel gradients, high hydraulic roughness and an initially abundant but rapidly depleted
supply of volcaniclastic sediment. These controls on, and impacts of, jökulhlaups are
important for distinguishing high-magnitude water-sediment inputs to the North Atlantic,
for recognising jökulhlaups in the rock record and for flood hazard mitigation in similar
landscapes and upon glaciated volcanoes.