Jökull - 01.01.2010, Page 194

M. Da̧bski and P. Angiel
2L and 9). They are 8 m long on average and have
spacing between the stripes of 0.5–1.5 m. The width
of a single coarse stripe is typically about 45 cm. Sort-
ing is limited to about 15 cm in depth.
35
53
70
0 cm
45 cm
volcanic ash
fine-grained trans located regolith
weathered volcanic breccia with
abundant res idual stones
lithified volcanic breccia
Simplied genetic classication:
Figure 9. Cross-section of a large-scale sorted stripe
in the southern part of Skálabjörg.– Þversnið af lag-
skiptri botnurðarrönd.
DISCUSSION
Upper, remote parts of the Skálabjörg nunatak
constitute a steep and weathered ridge. Taking into
consideration: 1) the fact that they must have been ice-
free at least since the end of the Pleistocene glaciation;
2) very steep slopes of the upper parts of the ridge; and
3) the cool maritime climatic conditions, we predict
that the major morphogenetic processes over there
have been frost weathering, rock avalanches and talus
accumulation. Therefore a typical periglacial zone
(Łoziński, 1912) has been developing on the nunatak.
The southern part of the Skálabjörg nunatak was tota-
lly covered by glacial ice in pre-LIA times as proved
by abraded bedrock surfaces with visible glacial striae
and slight ice-moulding of local hills.
After the most elevated parts of the study
area became deglaciated, paraglacial denudation,
fluvial and aeolian erosion of recent glacial sedi-
ments commenced (Ballantyne, 2002) together with
periglacial weathering of bedrock. Deglaciation of the
southern part of Skálabjörg elevated above the highest
moraine ridge occurred probably in pre-historic times
(Gudmundson, 1997). This could be deduced from
the following: 1) glacially abraded bedrock surfaces
on local hills are highly weathered, 2) there are
no glacial accumulation landforms leading to the
conclusion that they must have been eroded long time
before the LIA, 3) there is a record of several stages of
solifluction within the slope covers, allowing to infer
that this area has been free of glacier-ice for millennia
rather than centuries.
During the LIA maximum still-stand of Breiða-
merkurjökull, the highest lateral moraine ridge (later-
al moraine) was developed at the elevation of app-
roximately 700 m a.s.l. Depth of ground freezing and
development of ground ice was probably significant
during the LIA, because of climate deterioration and
proximity of glacier ice which additionally cooled
the nunatak surface and delivered water in abund-
ance. Gradually, poorly consolidated deposits started
to undergo solifluction and shallow sorting to produce
sorted stripes. Such periglacial processes were
favoured during at least 200 years of the LIA duration
(Bradwell et al., 2006).
Lichenometrical analysis indicate that the initial
exposure and stabilisation of the highest moraine
ridge, resulting from onset of Breiðamerkurjökull
retreat, occurred no earlier then the end of the 19th
century. This is in accordance with previous works
of Evans and Twigg (2002) and rather contradicts
recent findings of Bradwell et al. (2006). However,
the glacier could have reached its maximum extent
at Skálabjörg much earlier, possibly at the end of the
18th century, as suggested by Bradwell et al. (2006),
and remained fairly stationary for at least 100 ye-
ars. New mineral material was continuously deliv-
ered to the LIA moraine ridge causing unsuitable and
inhospitable conditions for lichens, therefore thalli
could establish themselves only since the onset of
Breiðamerkurjökull retreat.
194 JÖKULL No. 60