Jökull - 01.01.2012, Blaðsíða 117

Glacier changes in the marginal zone of Sólheimajökull
(e.g. Dunai, 2010). The sampled surfaces appeared
fresh and unweathered, and we corrected for slope
and topographic shielding (Dunai, 2010). The sam-
ples were dated using the cosmogenic 36Cl nuclide.
Samples were processed at the PRIME Lab at Purdue
University, Indiana, USA. For calculation of the ex-
posure age, geochemistry and specific gravity of the
sample must be known. The samples were analyzed
by Activation Laboratories (ACTLABS), Canada, by
a combination of lithium metaborate/tetraborate fu-
sion inductively coupled plasma mass spectrometry
(ICPMS) for major elements and by traditional solu-
tion ICPMS for trace element analysis using a Perkin
Elmer Sciex ELAN 6000 ICPMS. Cl concentrations
were determined by instrumental neutron activation
analysis (INAA) and B was analyzed by prompt
gamma neutron activation analysis (PGNAA). Spe-
cific gravity was determined on drilled cores from the
samples by ACTLABS. Ages were calculated using
the PRIME Lab calculator which computes surface
exposure ages according to Phillips et al. (2001).
RESULTS
Geomorphology of the Sólheimajökull forefield
The glacier forefield is dominated by numerous
end-moraine and lateral-moraine ridges dissected by
glaciofluvial erosion (Figures 3–4). The moraine
ridges are generally best preserved east of the river
Jökulsá á Sólheimasandi. The proximal 2 km of the
glacier forefield are formed by glacier advances dur-
ing the LIA and later. The end-moraine ridges in this
part of the forefield are 1–2 m high, 5–10 m wide,
and can be traced as up to 400 m long ridge segments.
River-cut sections show that the ridges consist mainly
of diamict. The ridges display moderately developed
saw-tooth pattern that mirror splaying crevasses and
small sub-lobes of the palaeo-ice margins (Figures 4
and 5B). Minor ponds or peat bogs occur immedi-
ately proximal to many end-moraine ridges, resem-
bling small-scale hill-hole pairs. The most prominent
end-moraine ridges represent the major LIA glacier
advances (Krüger et al., 2010).
A distinct end-moraine ridge marks the outermost
position of the advance that culminated in 1995. This
ridge is sharp-crested, 2–3 m high and 5 m wide. The
ridge is cut by fluvial erosion into small segments of
up to 100 m in length. It consists of diamict with
several large boulders deposited on the ridge. The
aerial photographs from 1996 document the age of
this ridge, and show that it was initially more contin-
uous. Proximal to the end moraine from 1995, small
moraine ridges occur. They are well-defined, up to 0.4
m high and 0.5–1 m wide, and occur in segments up
to 200 m in length. Field observations in the forefield
since 2004 confirm that the ridges are annual moraines
forming at the peak of each winter advance by the
end of the accumulation season (Figures 4 and 5C).
Their preservation potential is low due to fluvial ero-
sion, heavy rain, snowmelt, and tourist traffic.
The most prominent landforms in the Sólheima-
jökull forefield are the lateral moraines to the south-
east of the glacier (Figures 4 and 5A). They constitute
distinct ridges, up to 5 m high, 15–20 m wide, and
up to 1300 m long. The lateral moraines are com-
posed of diamict and numerous boulders are scattered
on their surface. The central part of the most distal lat-
eral moraine is located at 380 m a.s.l., approximately
150 m above the current (2010) lateral glacier margin.
Similar lateral moraines occur above the valley side
further south (Figure 4). One distinct lateral moraine
was identified above the western valley side.
Between the end-moraine ridges in the central
forefield, the landscape is characterized by ground
moraine. Small drumlins or drumlinoids up to 35 m
in length and with a c. 2 m relief occur between the
ridges (Figure 4 and 5B). It is likely that these small
drumlins represent overridden, streamlined remnants
of end moraines. A section in one drumlin proximal
to the 1995 end moraine reveals a core of extremely
firm basal till (Schomacker et al., 2010). Up to 50 m
long flutes are present in the recently deglaciated ter-
rain proximal to the 1995 end moraine. Similar to the
annual moraines, they have a very low preservation
potential and rapidly weather away.
In the ice-marginal area, where the glacier is cur-
rently retreating into a depression, large outwash fans
and an esker are underlain by dead-ice (Figure 4 and
5F). The esker is still emerging from the glacier, re-
vealing a sinuous 7–10 m high ridge of coarse gravel
JÖKULL No. 62, 2012 115