Jökull - 01.01.2012, Page 108

S. Guðmundsson et al.
Table 5. Surface elevation change in the ablation area deduced from Figures 4a-b, 5a-b and lateral moraines and
other geomorphological features in Kotárgil. – Tafla 5. Mælipunktar fyrir yfirborðsbreytingar á leysingarsvæði
samkvæmt myndum 4a-b, 5a-b og jaðarurðum í Kotárgili.
data points description latitude longitude alt. 2011 (m) alt. 1891 (m)
r1 crevasse area 63.9536 16.7007 950 982
rf1 peak of Rótarfjall 63.9547 16.7091 946 –
rf2 N tip of Rótarfjall 63.9540 16.7118 936 –
rf3 W side of Rótarfjall 63.9554 16.7110 881 911
rf4 W side of Rótarfjall 63.9544 16.7126 840 872
steðji1 ridge 63.9420 16.6801 970 –
steðji2 ridge 63.9412 16.6810 960 –
m4 lateral moraine 63.9571 16.7341 650 720
m3 lateral moraine 63.9553 16.7400 570 660
m2 lateral moraine 63.9520 16.7466 400 510
m1 lateral moraine 63.9492 16.7507 340 520
Surface lowering on the glacier plateau?
To resolve possible elevation changes of the ice
plateau of Öræfajökull, the 1904 map and the 2011
DEM were collimated (Figures 10a-b). Minor dis-
tortion was observed on the plateau, compared to the
level of deviation in the lower rugged terrain of the
mountain massif. The difference in elevation regi-
stered on the trigonometrical points above 1700 m is
shown in Table 6. The elevation of the glacier points
is on average 12.3 m higher on the 1904 map than
the LiDAR DEM, and 11.9 m higher on the peaks or
nunataks. This dissimilarity also applies to the ice-
covered Hvannadalshnúkur. The peak was measured
in 1904 at an altitude of 2119 m. The summit is 2110
m high according to the new DEM, which confirms
recent measurements by the Glaciological Society of
Iceland (1993 and 2004) and the National Land Sur-
vey of Iceland in 2005 (Guðmundsson, 2004; Morg-
unblaðið, 7th of August 2005). The surveying of the
Öræfajökull ice cap by the Danish General Staff, was
based on optical triangulation in several steps over
long distances from the lowland through peaks in Ör-
æfajökull and Skaftafellsfjöll (Figure 1, Koch, 1905).
DISCUSSION
Surface elevation changes of Kotárjökull are negligi-
ble at high elevations, increasing to maximum thin-
ning of 180 m, of the former terminus in the gorge.
Nowhere else along the southeastern edge of Vatna-
jökull, are glacier surface elevation changes since
the LIA maximum recorded continuously downward
from the ice divide to the terminus. The surface low-
ering at the glacier snout is similar to what has been
observed on other outlet glaciers of Vatnajökull to
the west and east of Kotárjökull (Hannesdóttir et al.,
2012). Comparable total volume loss over the 20th
century is reported for Hoffellsjökull and its neigh-
bouring southeastern outlet glaciers, on the order of
20–30% (Aðalgeirsdóttir et al., 2011; Hannesdóttir
et al., 2012). The well-preserved lateral moraines
are only found below the equilibrium line, hence lit-
tle field evidence attests to the former high stands of
the glacier in the accumulation area at its maximum
extent during the LIA. The historical oblique pho-
tographs are the only archive for surface changes in
the accumulation area.
106 JÖKULL No. 62, 2012