Jökull - 01.01.2020, Page 82

Little Ice Age advance of Kvískerjajöklar, Öræfajökull, Iceland.
Figure 5. An oblique aerial photograph of Kvískerjajöklar, taken from the airship Graf Zeppelin on July 17,
1930. The photographer was possibly Rolf Hermann Carl, who worked for the “Graphische Abteilung der
Luftschiffbau Zeppelin GmbH” from 1929 to 1934. Flugmynd af Kvískerjajöklum sem tekin var frá loftskip-
inu Graf Zeppelin 17. júlí 1930. Ljósmyndari var líklega Rolf Hermann Carl, sem starfaði fyrir „Graphische
Abteilung der Luftschiffbau Zeppelin GmbH“ frá 1929 til 1934.
et al. (2014). The elevation difference between the
LIAmax, 1880s and 1930 ice surface with respect to
the 2011 lidar DEM was estimated at several loca-
tions along the lateral 2011 ice margin, expressed by
a least-squares relationship (Figure 6) for elevations
between 650 m a.s.l. and 1600 m a.s.l., assuming in-
significant elevation changes at higher elevations. The
LIAmax elevation at the glacier margins was derived
by the equations zLIA = 0.895z2011+157 and zLIA =
0.920z2011+121 (in metres; Figure 6a), for the South
and North glaciers, respectively. The form of the
contour lines of the AMS map of 1945 was used to
create a DEM at LIAmax with a similar shape. A
photograph captured by the English traveler F. W. W.
Howell (1857–1901) from the nearby Breiðamerkur-
jökull outlet glacier, in 1891, supports our assumed
shape of the glacier surface in the accumulation area.
The 1930 glacier marginal elevations were estimated
by the equations z1930 = 0.910z2011+136 and z1930 =
0.948z2011+78, for the South and North glaciers (Fig-
ure 6b), respectively, and a surface map was drawn in
a similar manner based on the geometry depicted by
the contours of the 2010 map.
The glacier surface at elevations below the present
day glacier terminus was evaluated by simple ice-flow
modelling constrained by moraines (Glacier Recon-
struction Tool (GlaRe) in ESRI ArcGIS, Pellitero et
al., 2016). The model constructs glacier surface pro-
files along flow lines, assuming perfect plasticity of
ice, a basal shear stress of 100 kPa, and neglects shape
factors for the basal geometry. Seven flowlines were
modelled the North glacier which widens in the lower
JÖKULL No. 70, 2020 79