Jökull - 01.01.2016, Page 14

Eyjólfur Magnússon et al.
Table 2. The size of glaciated drainage basins of the 6 main rivers draining from Drangajökull (Figure 9), as-
suming full and no ice load. – Stærð jökulhulins hluta vatnasviða 6 stærstu jökuláa Drangajökuls út frá æstæðu
vatnsmætti þar sem gert er ráð fyrir fullu eða engu ísfargi.
River name Drainage area assuming full ice load (km2) Drainage area assuming no ice load (km2)
Jökulá í Leirufirði 27.8 27.5
Mórilla 35.8 37.1
Selá 25.6 28.7
Bjarnarfjarðará 18.0 16.8
Reykjarfjarðarós 19.4 20.5
Þaralátursós 7.5 5.6
Others 9.5 7.3
atmospheric level. Hence the water routes are likely
to be mostly controlled by the bed topography before
the ice disappears completely. Of the 6 main rivers
Mórilla in Kaldalón has the largest glaciated river
catchment (Table 2), draining 25% of the entire ice
cap, while Jökulá in Leirufjörður and Selá drain re-
spectively 19% and 18% of the entire ice cap (assum-
ing full ice overburden). Other rivers drain smaller
fraction of the ice cap.
By combining the obtained volume of Dranga-
jökull in July 2011 with the geodetic record of vol-
ume change in 1946–2011 (Magnússon et al., 2016)
a record was obtained of the ice cap absolute volume
showing its decadal variations (Figure 10). All vol-
umes were corrected towards the start of the glacio-
logical year (start of winter, ∼1 October) to mini-
mize effects of seasonal variations on the ice cap vol-
ume caused by variable dates of the DEMs, varying
from late June until early October (details explained
in Magnússon et al., 2016). The ice cap volume in au-
tumn 2014 was also calculated. It is deduced from a
surface DEM derived using optical stereo images ac-
quired by the Pléiades satellite (Belart et al., in open
review, 2016). The images were acquired 14 October
after the first winter snow fall. By applying a roughly
approximated relation between precipitation in Litla-
Ávík (weather station operated by the Icelandic Mete-
orological Office) ∼40 km southeast of Drangajökull
and the snow fall on the glacier (Belart et al., in open
review, 2016) 0.5±0.3 m was subtracted from the
DEM to represent the glacier surface on 1 October.
The glacier volumes in spring 2014 and 2015 (blue
dots in Figure 10) give an idea of the seasonal vol-
ume fluctuation of Drangajökull. These are obtained
Figure 10. The volume evolution of Drangajökull ice
cap since 1946. The black dots are obtained from the
bed DEM and surface DEMs at various dates in 1946-
2014 (Jóhannesson et al., 2013; Magnússon et al.,
2016; Belart et al., in open review, 2016). Volumes
are seasonally corrected towards the end of the glacio-
logical year (see Magnússon et al., 2016 for details).
The blue dots correspond to volume estimated from
spring surfaces of the ice cap in 2014 (from DGNSS
measurements obtained during the RES-survey) and
Pléiades DEM in May 2015. – Þróun heildarrúmmáls
Drangajökuls frá 1946. Svartir punktar gefa til kynna
rúmmál að hausti, fyrst haustið 1946, síðast haust-
ið 2014. Bláir punktar sýna rúmmál jökulsins í mars
2014 og maí 2015.
14 JÖKULL No. 66, 2016