Jökull - 01.01.2012, Side 110

S. Guðmundsson et al.
Table 6. Selected trigonometrical points on the glacier plateau (g) and peaks (p) of Öræfajökull ice cap, used
to compare their elevation (see Figure 10a-b) from the LiDAR DEM and the 1904 map. Locations from the
LiDAR DEM. – Tafla 6. Samanburður á hæð nokkurra mælipunkta innan Öræfajökulsöskjunnar milli korts
danska herforingjaráðsins frá 1904 og LiDAR-hæðargrunns. Þríhyrningsmælipunktar á tindum (p) og á jökli
(g) sem sýndir eru á 1904 kortinu (sjá mynd 10).
Location x (m) y (m) zLiDAR (m) z1904map (m) ∆ z (m)
a Sveinstindur (p) 64.0095 16.6181 2033 2044 11
b) Eystri Hnappar (p) 63.9799 16.6243 1753 1758 5
c) Vestari Hnappar (p) 63.9755 16.6382 1838 1851 13
d) Rótarfjallshnúkur (p) 63.9769 16.6613 1833 1848 15
e) Dyrhamar (p) 64.0074 16.7014 1902 1911 9
f) Hvannadalshryggur (p) 64.0068 16.7070 1830 1841 11
g) west face of Hvannadalshnúkur (p) 64.0120 16.6924 1870 1879 9
h) Tindaborg (p) 64.0240 16.6993 1727 1747 20
i) Þuríðartindur (p) 64.0817 16.6382 1727 1741 14
j) Hvannadalshnúkur (g) 64.0142 16.6771 2110 2119 9
k) center of caldera (g) 64.0048 16.6392 1843 1845 2
l) ice divide of Hrútárjökull1 (g) 64.0012 16.6098 1912 1927 15
m) ice divide of Hrútárjökull2 (g) 63.9982 16.5932 1827 1840 13
n) Tjaldskarð (g) 64.0421 16.6617 1824 1844 20
o) Snæbreið (g) 64.0256 16.6457 2028 2041 13
p) Jökulbak (g) 64.0531 16.6752 1911 1922 11
q) peak NE of Sveinstindur (g) 64.0144 16.6102 1951 1962 11
r) SW rim of caldera (g) 63.9904 16.6801 1815 1846 31
s) acc. area of Fjallsjökull1 (g) 64.0576 16.6451 1710 1716 6
t) acc. area of Fjallsjökull2(g) 64.0496 16.6550 1807 1808 1
that Hvannadalshnúkur has lowered by 9 m during
the last 100 years, due to glacial melting, as a simple
comparison of the 1904 map and recent measurements
may indicate (Morgunblaðið, 2005).
SUMMARY
By combination of several photographic archives, a
recent DEM and field inspection, we delineate the
area and volume loss of Kotárjökull glacier since the
LIA maximum in the late 19th century. The thinning
is negligable above 1700 m and gradually increases
downglacier to 180 m near the terminus. The glacier
has lost a volume of 0.4 km3 (30%) and decreased
in area by 2.7 km2 (20%). We estimate an average
specific mass loss of 0.22 m w.e./yr.
Comparison of the Danish map from 1904 with
the LiDAR DEM, indicates that little or no eleva-
tion changes took place during the 20th century on
the Öræfajökull plateau. This also applies to the sum-
mit Hvannadalshnúkur, and we conclude whether this
may be explained by surveying errors rather than sur-
face lowering, due to reduced glacier mass balance.
Acknowledgements
We used the LiDAR-data on a processing stage with
permission from the Icelandic Meteorological Of-
fice and the Institute of Earth Sciences at the Uni-
versity of Iceland. We thank Þorsteinn Sæmunds-
son, astronomer for helpful discussion on calculating
glacier surface elevation changes by comparing dupli-
cate photographs. Discussions with Eyjólfur Magnús-
son, Finnur Pálsson on ice thickness, ice flow, and the
response of glaciers to climate change, and Magnús
108 JÖKULL No. 62, 2012