Jökull - 01.01.2012, Side 150

E. Magnússon et al.
(Gudmundsson and Högnadóttir, 2007; Guðmunds-
son, 1999) suggesting that the area of volcanic activity
has been propagating southwards. Further geological
studies are however needed to verify if this hypothet-
ical caldera is real.
CONCLUSIONS
A detailed analysis of RES-data from Öræfajökull
and an accurate high resolution surface DEM have
been used to construct a comprehensive DEM of the
bedrock underneath the ice cap of Öræfajökull and the
distribution of ice stored within it. Based on this we
make the following key observations:
The ice in the ablation area of Öræfajökull is up
to 550 m thick, covering deep troughs, which reach
more than 200 m below current sea level. It would
take ∼4000 years to excavate these troughs into a pre-
existing sediment plain given the present rate of sed-
iment transport in the main rivers draining from Ör-
æfajökull. Hence it is unlikely that the troughs were
entirely formed during the Little Ice Age. Large lakes
will probably replace the glacier in these troughs in
the coming decades.
The distribution of ice volume and area of the out-
let glaciers of Öræfajökull vary significantly suggest-
ing a variable glacier response to changes in climatic
conditions from one outlet glacier to another. The
high accumulation area of some glaciers (e.g. Kvíár-
jökull) will secure their existence in the foreseeable
future while relatively little but permanent tempera-
ture change (0.5–1.0 ◦C) resulting in ∼100 m rise in
ELA may cause others (e.g. Morsárjökull) to decrease
to only a fraction of their present size or disappear
completely.
The caldera of Öræfajökull holds 4.3 km3 of ice
and the maximum ice thickness is 540 m. Most of the
caldera lies within the Kvíá drainage basin, while the
remainder is mainly within the Virkisá river basin.
The lowest pass cutting the caldera rim is at
∼1570 m a.s.l., located underneath Kvíárjökull.
Hence, if all the ice mass within the caldera were
melted during an eruption but the bedrock topogra-
phy would remain intact, 1/3 of the meltwater would
remain within the caldera, putting the upper limit of
flood water volume down to ∼2.6 km3. The second
main pass, towards Fall- and Virkisjökull, is at ∼1610
m a.s.l.
The floor of the caldera is smooth and volcanic
features appear almost absent. An exception is a
mound near the water divides between Kvíá and Virk-
isá drainage basins beneath 400 m of ice. An eruption
at this location may cause massive jökulhlaups both
towards east beneath Kvíárjökull and west beneath
Virkis- and Falljökull. A topographic step within the
caldera suggests a separate and probably more recent
caldera formation, ∼150 m deep and ∼6 km2 in area.
Acknowledgements
The Iceland Glaciological Society, Iceland Road Ad-
ministration and Landsvirkjun (the National Power
Company of Iceland) are thanked for assisting the
RES survey of Öræfajökull. Óliver Hilmarsson, Einar
Ísfeld Steinarsson, Alexander H. Jarosch, Hlynur
Skagfjörð, Haukur Elvar Hafsteinsson, Sveinbjörn
Steinþórsson, Ágúst Þór Gunnlaugsson and Sigurlína
Héðinsdóttir are thanked for field work assistance.
Kvískerjasjóður Fund and the Parliament of Iceland
supported the work financially. The field work in
2012 was funded through the Icelandic Meteorolog-
ical Office, by the Icelandic government’s integrated
risk assessment program for volcanoes in Iceland. Fi-
nancial support for LiDAR mapping of glaciers in
Iceland has been provided by the Research Fund of
Iceland, Landsvirkjun Research Fund, the Icelandic
Road Administration, the Reykjavík Energy Environ-
mental and Energy Research Fund, the National Land
Survey of Iceland, and the Klima- og Luftgruppen
(KoL) research fund of the Nordic Council of Min-
isters. SPOT 5 images were made available by the
International Polar Year SPIRIT project. This publi-
cation is contribution number 16 of the Nordic Cen-
tre of Excellence SVALI, ’Stability and Variations of
Arctic Land Ice’, funded by the Nordic Top-level Ini-
tiative (TRI). We thank Þorvaldur Þórðarson and an
anonymous reviewer for very constructive reviews,
that helped to improve the paper. Leó Kristjánsson is
thanked for thorough proofreading of the manuscript.
148 JÖKULL No. 62, 2012