Jökull - 01.12.1983, Síða 119

the position occupied by ice around 1940. The ad-
vance probably terminated about 1950 beforefurth-
er retreat to its minimum position in the mid-1970’s
(Caseldine and Cullingford 1981) and then readvanc-
ed to the 1981 position. This sequence would ex-
plain why Eythórsson (1963) only found 46 m of net
retreat between 1939, a position close to the ridge on
which Station 6 stands, and 1953, a position which
may be marked by one of the two series of ridges
between H and J. Comparison with figures for
other Icelandic glaciers quoted by Eythórsson (1963)
shows some evidence for contemporaneous advanc-
es, especially on Mýrdalsjökull where there were
advances in the late 1940’s and early 1950’s, al-
though such comparisons should be treated with
caution. The ridge produced by the advance which
terminated in 1950 also marks the principal change
in plant species found across the foreland with Salix
herbacea and Polygonum vivipamm occurring consist-
ently outside the ridge as dominants, only being
found as isolated occurrences closer to the ice. The
Iichen dates would confirm the earlier findings of
Persson (1964) and Stork (1963) who observed these
species only on ground deglaciated for more than 30
years.
CONCLUSION
The studies undertaken in 1981 which extended
work started in 1979 has now led to the develop-
ment of a more reliable chronology for the recent
deglaciation of Gljúfurárdalur as summarised
below:
a) Gljúforárjökull began to retreat from its „Little
Ice Age” maximum during the last decade of
the 19th century and overthe next twenty years
retreated about 250 m.
b) Between the middle of the second decade of the
20th century and 1930 this rate of retreat slow-
ed and there may have been a short phase of
glacial advance or stillstand.
c) There was more rapid retreat in the 1930’s,
probably of the order of 200 m with the format-
ion of more extensive ridge systems in the mid-
1930’s. By 1940 the margin of Gljúfurárjökull
lay close to the position now defined by the
major ridge system on which Station 6 stands.
d) Retreat continued to the position marked by
the 1946 aerial photograph and possibly slight-
ly beyond this point before a period of read-
vance in the late 1940’s which eventually form-
ed, at its maximal extent, the ridge system
mentioned in c). This was completed in 1950-
51.
e) Gljúfurárjökull then retreated to its minimum
position in the mid-1970’s before advancing by
up to 50 m between 1977 and 1979, with a
further 30 m of advance between 1979 and
1981.
AC KN OW LEDGEM ENTS
Deborah Barham, Nigel Gardner, Peter Hookham,
Christine Hudson, Rosematy Johnson, Kathryn Padgham,
Allison Tipper and Catriona Wildall contributed in various
ways to the work described here. Dr. Jack Jarvis was
responsible for much oj the Expedition organisation and
helped with the work as well as commenting on the manu-
script andproviding unpublished data. Dr. Robin Culling-
ford also commented on an early draft of this paper. All
members ojthe Expedition were gratejul to Hjörtur Thórar-
insson and his wije at Tjórn Jor their continuing hospitality
and to the people oj Svarjaðardalur and Skíðadalur Jor
allowing us to work in the area. The Icelandic Research
Council kindly allowed permission to continue the work in
the glacier and the studies would not have been possibte
without the help oj our many sponsors. TheJigures were all
prepared in the Department oj Geography in the University
oj Exeter.
REFERENCES
Andrews, J. T. and P.J. Webber, 1964: A Lichenometr-
ical study of the northwestern margin of the
Barnes Ice Cap: a geomorphological technique.
Geog. Bulletin, 22: 80- 104.
Beschel, R.E., 1950: Flechten als Altersmasstab re-
zenter Moránen. Zeit. fúrGletsch. und Glaziol.,
1: 152-161.
Beschel, R.E., 1961: Dating rock surfaces by lichen
growth and its application to glaciology and
physiography (lichenometry). In Rasch, G.O.
(ed.) Geology of the Arctic, 2: 1044- 1062.
Calkin, P.E. and J.M. Ellis, 1981: A cirque-glacier
chronology based on emergent lichens and
mosses. Arctic and AlpineRes., 27: 511 -515.
Caseldine, C.J. (compiler) 1981: Reportofthe Exeter
University North Iceland Expedition 1979. 53
pp.
Caseldine, C.J. and R.A. Cullingford, 1981: Recent
mapping of Gljúfurárjökull and Gljúfurárdalur.
Jökull, 31: 11-22.
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