Jökull - 01.01.2010, Blaðsíða 195

The retreat of Breiðamerkurjökull at Skálabjörg, SE Iceland
The two glacially abraded boulders found on the
eastern slope of the nunatak near the highest moraine
ridge account for a hypothesis that the glacier’s max-
imum extent in the LIA was prior to the formation of
the highest moraine ridge. Relatively young age of the
striated surfaces of the boulders can be inferred from
freshness of the surfaces and the fact that the boulders
are not overgrown by large lichens. Deposition of the
boulders could occur in 18th century (Bradwell et al.
2006), but the event is not marked by any glacial land-
form, so there was no glacial still-stand that time.
Sorted stripes and solifluction tongues and lobes
developed suggesting significant colluvial downslope
transportation. High rainfall values in the study
area now actively conserve the stripes by erosion rill
formation (Washburn, 1956; FitzPatrick, 1960). The
absence of expected small-scale sorted nets, which are
quite common in maritime periglacial environments
(Thorarinsson, 1953; Kim, 1967; Ballantyne, 1996;
Da̧bski, 2005) can be explained by lack of frost-
susceptibility of the uppermost sediment layer, inter-
preted as volcanic ash.
Below the top surface of the southern part of
Skálabjörg, the ground surface slopes steeply down
to the glacier margin. Gradual downslope steepen-
ing of the slopes may be an effect of recently en-
hanced glacial erosion due to increased glacial flow
and enhanced calving into Jökulsárlón (Björnsson et
al., 2001). Slopes inclined at 14◦ to 32◦ are subj-
ect to paraglacial reworking, e.g. gully development
(Ballantyne, 2002), rather than periglacial processes.
Time of formation of the lateral moraines, visible in
the lower parts of slopes, probably correlates with per-
iods: 1950–1955, 1968–1973, 1975–1987 deduced by
Evans and Twigg (2002) as periods of Breiðamerkur-
jökull margin re-advances.
CONCLUSIONS
Retreat of Breiðamerkurjökull at Skálabjörg after the
Little Ice Age maximum started in years AD 1896–
1930. The average rate of ice surface lowering has
been from 0.8 to 1.3 m/yr. Below the LIA moraine
ridge, five to seven subtly visible lateral moraine
ridges record brief glacial advances or still-stands.
Deglaciation has prompted the development of two
ice-dammed lakes which, in turn, has accelerated fur-
ther ice melting in Fossadalur and at the southermost
end of Skálabjörg. Recently deglaciated slopes are
too unstable (steep) to bear imprints of periglacial
modification. This however does occur, to a modera-
te degree, on the undulating top surface of the sout-
hern part of the nunatak where solifluction forms are
well developed. Conditions typical for a periglacial
zone described by Łoziński (1912) are fulfilled in
the upper parts of the nunatak: the rocks are loca-
ted in mid-latitudes, there is a close proximity to a
large ice-cap, there are strong katabatic winds, the
landscape is mountainous, frost weathering is a major
morphogenetic factor and vegetation is sparse. Th-
erefore, Skálabjörg may be the answer to a question
put forward in the characteristic title of a paper by
French (2000) about possible existence of a classic
"periglacial zone"in the contemporary environmental
conditions.
Acknowledgement
The research was possible thanks to permits from the
Vatnajökull National Park and the Icelandic Institute
of Natural History. The authors would like to thank
María Ingimarsdóttir and the Icelandic Institute of
Natural History for help in logistics in the field and
satellite images. We thank Starri Heiðmarsson for
inspiration and assistance. Comments by reviewers
Tom Bradwell and Anders Schomacker are greatly
appreciated as well as editorial assistance of Bryndís
Brandsdóttir and two anonymous members of the ed-
itorial board.
ÁGRIP
Kortlagning á ummerkjum jökulhörfunar í suðurhluta
Skálabjarga í Eskjufjöllum gefur til kynna að hop
Breiðamerkurjökuls hafi hafist á árunum 1896–1930
og að yfirborð jökulsins hafi sigið 0,8–1,3 m árlega.
Fimm til sjö litlir samsíða jökulgarðar endurspegla
stutt framrásarskeið eða kyrrstöðu jökulsins á þessu
tímabili. Landmótunarkortlagning á ummerkjum jök-
ulhörfunarinnar staðfestir mikla vind- og frostveðrun
á svæðinu. Tvö ísstífluð uppistöðulón sem myndast
hafa tímabundið í Fossadal og við suðurenda Skála-
bjarga hafa ýtt undir hop jökulsins.
JÖKULL No. 60 195