Jökull - 01.01.2013, Blaðsíða 91

Reviewed research article
Mass balance of Mýrdalsjökull ice cap accumulation area and
comparison of observed winter balance with simulated
precipitation
Hálfdán Ágústsson1,2,3, Hrafnhildur Hannesdóttir4,5, Thorsteinn Thorsteinsson3,
Finnur Pálsson5 and Björn Oddsson4,6
1Institute for Meteorological Research, Orkugarði, Grensásvegi 9, 150 Reykjavík
2Faculty of Physical Sciences, University of Iceland, VRII, Hjarðarhagi 2–6, 101 Reykjavík
3Icelandic Meteorological Office, Bústaðavegur 7–9, 150 Reykjavík
4Faculty of Earth Sciences, University of Iceland, Askja, Sturlugata 7, 101 Reykjavík
5Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, 101 Reykjavík
6Department of Civil Protection and Emergency Management,
National Commissioner of the Icelandic Police
Corresponding author: halfdana@gmail.com
Abstract — The Mýrdalsjökull ice cap at the south coast of Iceland receives precipitation from the frequently
passing extratropical lows, making the region the wettest in Iceland. Most of the ice cap’s accumulation area
is a gently sloping plateau (1350–1510 m a.s.l.) within the caldera rim of Katla central volcano, feeding large
outlets to the north and east. The oldest mass balance survey data are from 1944 and 1955. Here, mass
balance measurements on the plateau, carried out 2001 and annually since 2007, are described and analyzed.
Additionally, the winter mass balance is compared with precipitation estimates based on synoptic observations
of precipitation at sea level and from high-resolution numerical simulations made with an atmospheric model.
The measured specific winter balance at four locations above the equilibrium line was in the range 3.4–7.8 mwe
(water equivalent) with a maximum winter snow thickness in excess of 12 m. The summer mass balance was
highly variable (-0.9 – -3.1 mwe) and the annual mass balance at the plateau had a high spatial and temporal
variability (2.1–5.9 mwe). A comparison between measured winter balance and observations of precipitation
at sea level, suggests that the plateau of Mýrdalsjökull receives on average 1–1.8 mwe of precipitation during
summer. Results from the atmospheric simulations compare well with the measured winter balance and the
estimated summer precipitation at the survey sites. The winter balance as well as the precipitation are among
the highest reported in Iceland, and parts of the ice cap may annually receive up to 10 mwe of precipitation.
INTRODUCTION
Mýrdalsjökull ice cap on the south coast of Ice-
land (Figure 1) covers an area of ≈590 km2 with a
volume of ≈140 km3 (Björnsson and Pálsson, 2008),
and is the fourth largest ice cap in Iceland.
The ice cap rises relatively steeply from 120 m
to 1510 m above sea level (a.s.l.), with an ice-filled
caldera plateau (60 km2) at an altitude of 1300–
1350 m a.s.l., surrounded by peaks rising 100–200 m
above the plateau which is the main accumulation
area of the ice cap. Numerous surface depressions,
JÖKULL No. 63, 2013 91