Jökull - 01.01.2012, Blaðsíða 115

Glacier changes in the marginal zone of Sólheimajökull
the potential of cosmogenic exposure dating on late
Holocene landforms. Because the chronology of land-
forms at Sólheimajökull is generally well established
from tephrochronology and 14C dating, the site of-
fers a good possibility to explore cosmogenic expo-
sure dating. In order to quantify the glacier changes
during the last c. 50 years, time series of DEMs were
investigated.
SETTING
The 11 km long Sólheimajökull outlet glacier drains
the southwestern part of the Mýrdalsjökull ice cap
through a 1–2 km wide valley (Figure 1). The glacier
descends from c. 1350 to 100 m a.s.l. where it termi-
nates as a 1.5 km wide glacier tongue. The central part
of the snout now terminates in a small ice-marginal
lake; the rest of the margin terminates on sediments.
Meltwater from Sólheimajökull drains southwards to
the Atlantic Ocean through the river Jökulsá á Sól-
heimasandi (also known as Fúlilækur). The climate
is humid and mild with a mean annual air tempera-
ture of 7.8◦C and a mean annual precipitation of 1810
mm (data for 1979–2008 from the Icelandic Meteoro-
logical Office station at Vatnsskarðshólar, 20 m a.s.l.,
30 km SE of Sólheimajökull). However, the central
areas of the Mýrdalsjökull ice cap receive as much as
10,000 mm/yr of precipitation (Crochet et al., 2007).
The marginal fluctuations of Sólheimajökull have
been recorded annually since 1930 by the Iceland
Glaciological Society (Figure 2). The data show a to-
tal 977 m of retreat between 1930 and 1969. After
that, the glacier advanced 495 m in the period 1970–
1995. Since then, Sólheimajökull has retreated 750 m
and is presently (2010) 1232 m behind its 1930 posi-
tion. During its LIA maximum, Sólheimajökull ter-
minated approximately 2 km further out than its 2010
margin.
METHODS AND DATA
Aerial photographs and digital elevation models
Fourteen series of aerial photographs from the pe-
riod 1938–2009 were used for mapping. Orthorec-
tified imagery and DEMs were produced by stereo-
photogrammetry for four selected years. Fifteen
Ground Control Points (GCPs) were measured by dif-
ferential GPS in the field prior to the image analyses,
and calibrated camera data were available. All GCPs
were time-homologous; hence they could be identi-
fied in all image series. The accuracy of the GCPs
is at a sub-meter level. The processing of imagery
was carried out at a digital photogrammetric worksta-
tion, using BAE Systems Socet Set 5.2 with a Stereo-
Graphics ZScreen monitor for stereoscopic viewing.
An overview of the aerial photographs and derived
DEMs is given in Table 1.
In 2010, airborne LiDAR measurements were car-
ried out at Mýrdalsjökull as part of a larger mapping
effort of Icelandic ice caps (data from the Icelandic
Meteorological Office and the Institute of Earth Sci-
Figure 2. Cumulative glacier-marginal variations of Sólheimajökull, 1930–2010. From the database of the Ice-
land Glaciological Society. – Mynd sem sýnir sporðabreytingar Sólheimajökuls frá 1930 til 2010. Gögn frá
Jöklarannsóknafélagi Íslands.
JÖKULL No. 62, 2012 113