Jökull - 01.01.2012, Page 166

S. Brynjólfsson et al.
type glaciers like the Deildarjökull glacier. This
is considered to highlight the potential of the new
landsystems model to distinguish between surge-type
and non-surging cirque glaciers in Iceland.
We suggest that detailed mapping of the geo-
morphology of Tröllaskagi cirque glaciers, using the
landsystems model outlined above, might reveal more
surge-type glaciers.
Permafrost and potential affect on the landsystems
model and surge behaviour
Judging from permafrost and local climate studies in
northern Iceland and the Tröllaskagi area presence of
permafrost is possible in the vicinity of glaciers at
Tröllaskagi (Etzelmüller et al., 2007; Farbrot et al.,
2007a; 2007b). Presence of permafrost in the foreland
of glaciers in Tröllaskagi might affect the applicabil-
ity of the landsystems model. If permafrost is present
and glacier ice with sufficiently thick supraglacial de-
bris layer is transported towards a terminal moraine
during a surge, the dead-ice may survive as long as
permafrost conditions prevail. In case of permafrost
the influence on the landsystems model could be that
dead-ice topography would not develop to any signif-
icant degree. However, dead-ice melting can be inten-
sive in permafrost area as has been reported from e.g.
Holmströmbreen on Svalbard (Schomacker and Kjær,
2008). If the debris cover thickness exceeds the depth
of the active layer, dead-ice melting is prevented. The
geomorphological environment of our study area ex-
tends from about 600 m a.s.l. to 900 m a.s.l. and dead-
ice topography was mapped up to 900 m a.s.l. indi-
cating absence of, or very restricted, permafrost at
present.
Murray et al. (2000) suggested that occurrence
of surges on Svalbard could be controlled by the
transition between frozen and unfrozen bed. If per-
mafrost is present in Tröllaskagi we consider it pos-
sible that polythermal surging glaciers exist (cf. Benn
and Evans, 2010). In that sense, permafrost could pos-
sibly contribute to surge activity. When a glacier mar-
gin is stagnant or frozen to its substratum during a qui-
escent phase, ice-flow down to the ablation area might
be reduced. This could make conditions for build-up
of the accumulation area more favorable and therefore
increase the probability for surge activity.
CONCLUSIONS
Studies of the two cirque glaciers, Búrfellsjökull and
Teigarjökull, have increased our knowledge on the na-
ture of small surge-type cirque glaciers. By studying
their geomorphology and sedimentology, a landsys-
tems model for small surge-type cirque glaciers has
been developed. The model could serve to identify
surge-type cirque glaciers in Iceland. Our study high-
lights that surge-type cirque glaciers leave distinct
fingerprints different from both non-surging cirque
glaciers and large surge-type glaciers that drain out as
broad lowland lobes from ice caps. The unique finger-
printing of the surge-type cirque glaciers is as follows:
1. Sediments are generally coarse, and at sur-
face often characterized by angular supraglacial
and englacial material considered to originate
mainly from rock walls that surround the accu-
mulation areas of glaciers.
2. River-cut sections close to the present margin
of Búrfellsjökull reveal that the glaciers also
deposit subglacial till. Because of the large
amounts of englacial and supraglacial debris,
the till is often covered and not visible on the
surface.
3. In front of Búrfellsjökull and Teigarjökull hum-
mocky moraine is prominent on the proxi-
mal sides of end moraines and extends often
over large areas. Dead-ice occurs, especially
in younger formations, indicated by sinkholes,
cracks, backslumping and collapse.
4. End moraines are usually small and irregular.
In some cases the moraines constitute a step in
the landscape up on to a debris sheet.
5. Small annual (retreat) moraines do not occur
in the glacier forefield of the surging cirque
glaciers.
6. Small crevasse-fill ridges occur in the glacier
forefield. Poorly developed flutes also occur,
but are relatively rare.
7. Low-amplitude ridges extending from the ab-
lation zone to the glacier forefields are inter-
preted as medial moraines that form as response
of folding of englacial sediments due to lateral
compression.
164 JÖKULL No. 62, 2012