Jökull - 01.01.2012, Page 118

A. Schomacker et al.
Figure 3. Oblique view towards Sólheimajökull on aerial photographs from 2009. Selected ice-marginal po-
sitions are shown. White lines indicate moraine ridges formed mainly prior to the 20th century, the Little Ice
Age (LIA) maximum (red line) position is from a prominent moraine ridge, the 1904 position is taken from
the Danish General Staff Map No. 69 NV, and the remaining positions are from aerial photographs. Vertical
exaggeration is ×2. – Skámynd af Sólheimajökli og svæðinu framan við hann 2009. Staða jökulsporðsins á
mismunandi tímum er sýnd með línum í mismunandi litum. Hvítar línur tákna jökulgarða sem myndaðir eru
fyrir 20. öld. Myndin er unnin út frá loftmyndum sem lagðar voru ofan á hæðalíkan. Hæðarýking er tvöföld.
and sand. It is ice-cored; hence it must have formed
in an englacial tunnel. The esker is both subject to
dead-ice melting and fluvial erosion and is not likely
to be preserved. In the central part of the valley, ac-
tive braided river plains occur (Figure 4 and 5D). They
are developing under normal discharge regimes by ac-
cumulation of sand, gravel, and cobbles. Minor out-
wash fans of sand fill up depressions between moraine
ridges (Figure 4 and 5E). A fan of meter-sized boul-
ders and coarse debris is present close to the position
of the 1996 ice margin with its apex located at the
1999 ice marginal position (Figure 4). The fan has a
hummocky surface and is coarser grained in its prox-
imal part. The creation of this fan was observed in a
jökulhlaup in July 1999 (Russell et al., 2010). Similar
coarse-grained fans are present further out in the val-
ley. Accordingly, they are interpreted as older jökul-
hlaup deposits (Maizels, 1991). Large channels, orig-
inating at the 1999 ice marginal position, have been
incised into the sediments (Figure 4 and 5C). The
largest one is approximately 25 m wide and 6 m deep.
The channels were eroded during the July 1999 jök-
ulhlaup and have not been draining meltwater since
then. The canyon-like morphology of the channels
demonstrates the extreme eroding forces during the
jökulhlaup which reached a peak discharge of c. 4000
m3s−1 (Russell et al., 2010).
Sedimentology – section 1
Section 1 is located at the eastern bank of Jökulsá
á Sólheimasandi c. 2 km from the 2007 ice margin
(Figure 4). The river-cut section is about 50 m long
and up to 16 m high. It documents the changing en-
vironments of the Sólheimajökull forefield and offers
insight into depositional processes prior to the LIA.
We did not observe any datable material in section
1. Twelve different sediment units are exposed in the
section (Figures 6–7). Those are described and inter-
preted in Table 2.
116 JÖKULL No. 62, 2012