Jökull - 01.01.2012, Page 109

Post-Little Ice Age volume loss of the Kotárjökull glacier,
Figure 10. Elevation difference of selected trigonometrical points on the high plateau of Öræfajökull ice cap,
between a) the LiDAR DEM (2011) and b) the 1904 map of the Danish General staff. Squares indicate points
on the glacier, and filled circles represent points on nunataks. Each location is marked with a letter correspond-
ing to Table 6. – Hæðarmunur á völdum mælipunktum á Öræfajökli milli a) LiDAR-hæðargrunns og b) korts
danska herforingjaráðsins frá 1904 er sýndur. Hver punktur er táknaður með bókstaf (sjá töflu 6). Kassar
tákna mælistaði á jökli en fylltir hringir sýna mælipunkta á tindum eða jökulskerjum.
No elevation change of the 5 km wide glacier
plateau covering the caldera is remarkable. The ice
cap has limited possibilities to expand, since any sur-
plus in mass balance will flow straight over the caldera
rim to lower elevations. The thickness change with
altitude observed between the end of the 19th century
and 2011 on Kotárjökull, provides a reference for fur-
ther studies of other outlet glaciers of Öræfajökull and
the southern edge of Vatnajökull.
The observed elevation anomaly of the trigono-
metrical points, along with calculated surface changes
in the accumulation area, raises the question whether
the geodetic survey of the plateau of Öræfajökull may
have been inaccurate by about 10 m (see Table 6).
We speculate whether this is due to errors, i.e. caused
by light refraction, across a surface with variable re-
flectance and changing temperature conditions (as de-
scribed in Böðvarsson, 1996). We therefore doubt,
JÖKULL No. 62, 2012 107