Jökull - 01.06.2000, Page 29

An ice-dammed lake in Jökulsárgil
a tunnel for some years, even if the glacier reverts
its recent trend and begins to recede. As long as the
tunnel exists and rates of tunnel closure exceed melt
rates for a long enough period, the threshold for tunn-
el closure is likely to be periodically crossed, and an
ice-dammed lake will continue to form at the site.
ACKNOWLEDGEMENTS
The majority of the research for this paper was carried
out whilst the author was in receipt of a Keele Uni-
versity Geography Department Research Studentship
under the supervision of Peter Knight. Funding for
fieldwork undertaken from 1989-91 was provided by
Keele University Geography Department, The Brit-
ish Geomorphological Research Group, The Keele
Research Association, The Geologists’ Association,
The Norton, Salisbury and Brailsford Educational
Foundation, The Dorothy Worthington Youth Trust,
Greenhall-Whitley Brewers Ltd., Letraset U.K. Ltd.
and Colgate-Palmolive Ltd. Funding for an observati-
onal field visit to Iceland in 1996 was provided
by The British Geomorphological Research Group,
Staffordshire University School of Sciences Small
Grants Fund and Staffordshire University Geography
Department. The Icelandic Research Council and the
Icelandic Council of Science kindly granted permissi-
on to undertake fieldwork in Iceland from 1989-91.
Peter Knight and Tim Harris assisted in the field.
Thanks to Helgi Björnsson for help in his capacity
as Icelandic collaborator, to Oddur Sigurðsson of
Orkustofnun for his responses to my questions about
Sólheimajökull and to Reynir Ragnarsson from Vík
for communicating his observations of Jökulsár-
gil. Thanks are due to both Wilf Theakstone and
Tony Parsons for their advice on this work, and
to Roger Ward for his assistance with elements of
computational ice physics. Tómas Jóhannesson made
some very helpful comments particularly concern-
ing some of the mathematical elements of the work;
his advice as a reviewer is gratefully acknowledged.
The author also appreciates the suggestions made by
a second anonymous reviewer. Rosie Duncan, Mal
Beech and Andy Lawrence prepared the photographs
and illustrations.
ÁGRIP
KÖNNUN Á AÐSTÆÐUM SEM LEITT GETA
TIL MYNDUNAR JÖKULSTÍFLAÐS VATNS
VIÐ SÓLHEIMAJÖKUL
Mikil hlaup komu fyrr á tímum úr jökulstífluðu jað-
arlóni í Jökulsárgili við Sólheimajökul (Thorarinsson,
1939). Á kortinu frá 1904 sést hvernig Sólheimajök-
ull stíflar gilið en þá lá jökullinn við mynni Fjallgils
(2. mynd). Hlaupin tóku af þegar jökullinn hörfaði, en
frá árinu 1969 hefur hann skriðið fram á ný um 500
metra og nær nú aftur vestur fyrir gilið. Talið er að
síðasta hlaupið hafi komið sumarið 1936.1 dag bræðir
Jökulsá rás við botn jökulsins sem viðheldur rennsli í
ánni og kemur í veg fyrir að vatn nái að safnast fyrir að
einhverju ráði í gilinu. Vettvangsrannsóknir okkar við
jaðar Sólheimajökuls á árunum 1989, 1990, 1991 og
1996 benda hins vegar til þess að lón myndist af og til
í Jökulsárgili. Líkanreikningar benda einnig til þess að
lón myndist tímabundið á veturna, þegar göngin sem
áin bræðir við botn jökulsins lokast.
REFERENCES
Ballantyne, C. K. and S. B. McCann. 1980. Short-lived
damming of a high arctic ice-marginal stream, Elles-
mere Island, N. W. T., Canada. Journal of Glaciology
25, 487-491.
Björnsson, H. 1992. Jökulhlaups in Iceland: prediction,
characteristics and simulation. Annals of Glaciology
16, 95-106.
Dugmore A. J. and D. E. Sugden. 1991. Do the anom-
alous fluctuations of Sólheimajökull reflect ice-divide
migration? Boreas 20, 105-113.
Einarsson, E. H., G. Larsen and S. Thorarinsson. 1980.
The Sólheimar tephra layer and the Katla eruption of
1357. Acta Naturalia Islandica 28, 24 pp.
Hooke, R. LeB. 1984. On the role of mechanical energy in
maintaining subglacial water conduits at atmospheric
pressure. Journal of Glaciology 30, 180-187.
Hooke, R. L., T. Laumann and J. Kohler. 1990. Subglacial
water pressures and the shape of subglacial conduits.
Journal of Glaciology 36, 67-71.
Iken, A. and R. A. Bindschadler. 1986. Combined mea-
surements of subglacial water pressure and surface
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