Jökull - 01.01.2016, Side 66

Paweł Molewski and Leon Andrzejewski
floated in the ice-dammed lake, as attested by drop-
stone structures in the glacilacustrine sediments. The
lake was feed by meltwaters, which probably formed
small fan deltas. After the lake disappeared, meltwa-
ters formed small alluvial fans on the terrace surface
(Figure 11B). These waters flowed out between the
glacier and Jökulgrindur in a south-westerly direction.
A debris flow formed on the melting glacier snout.
After degradation of the glacier snout the meltwater
flow on the terrace surface disappeared and a lower
flow system formed (Figure 11C). Since the kame ter-
race was partially destroyed (Figure 11D) by the sub-
sequent glacifluvial flow, the size of the lake cannot
be inferred from its present size.
The spatial relationships of the studied forms and
the range of the moraine deposits in the study area
suggest that the original width of the lake and ter-
race was about 250 m. The trace of the lake shoreline
preserved on Jökulgrindur’s slopes indicates that its
depth was at least a dozen metres.
CONCLUSIONS
The geomorphological and sedimentological studies,
as well as the analysis of cartographic and remote
sensing materials, have resulted in a reconstruction of
the main stages of the formation of relief and depo-
sitional environments in the northern part of Tungna-
árjökull’s marginal zone between the end of the LIA
and modern times. It has been shown that the vol-
canic substrate of the glacier forefield had a major
impact on the landforms and sediments in this part
of the marginal zone. Its main element is a system
of parallel Upper Pleistocene volcanic ridges oriented
northeast-southwest. The ridge of Jökulgrindur runs
parallel to the northern part of Tungnaárjökull’s snout,
which blocked the outflow of glacier meltwaters dur-
ing its subsequent advances.
The damming of meltwater outflow caused the oc-
currence of ice-dammed lakes in the northern part of
the marginal zone of Tungnaárjökull. The preserved
lake shorelines and small wave-cut platform, fossil
delta and kame terrace are evidence of their existence.
Figure 11. Model of the kame terrace, modified
from Molewski et al. (2005). A: Ice-dammed lake
phase; B: Meltwater flow phase; C: Erosion of the
kame terrace and degradation of dead glacial ice; D:
Preserved kame terrace. – Líkan af þróun jökullónsins
við norðvesturjaðar Tungnaárjökuls.
66 JÖKULL No. 66, 2016