Jökull - 01.01.2016, Blaðsíða 67

The marginal zone of Tungnaárjökull, Iceland
The lake shorelines and wave-cut platform doc-
ument the varied rates at which the water levels
dropped, until the complete disappearance of the
lakes. The disappearance of the ice-dammed lake in
the northernmost part of the glacier forefield (the
northern study area) is documented by the fine-
grained nature of the deposits, which probably repre-
sent its shore zone. Sedimentological studies of one of
the deltas which formed within an ice-dammed lake,
in contact with the stagnating glacier snout, showed
that it developed as a result of the deposition of sedi-
ments in an ice-dammed lake in conditions of hyper-
pycnal supply.
Sedimentological studies of the preserved frag-
ments of the kame terrace in the southern study area
show that it was formed in variable depositional con-
ditions, initially in an ice-dammed lake, and subse-
quently in conditions of meltwater flow in a south-
westerly direction.
The earliest stage of the formation of relief and
depositional environments in the northern part of
Tungnaárjökull was associated with the maximum ex-
tent of the glacier snout at the end of the nineteenth
century. Its record includes glacial forms and sedi-
ments on the ridge and western side of Jökulgrindur.
The ice-dammed lake which developed due to the
blocking of the meltwater outflow probably drained
before 1939.
The next development of this zone was associated
with the surge of 1945, when an ice-dammed lake
formed. An ice-dammed lake may also have appeared
during a surge in the years 1915–1920. In the opinion
of the authors, the preserved glacilacustrine forms and
deposits are associated with the surge of the glacier in
1945, at which time the glacier in part reached Jökul-
grindur. These forms and deposits are dated similarly
by Evans et al. (2009).
The last stage in the development of Tungnaár-
jökull’s forefield is connected with its recession fol-
lowing the 1945 and 1994–1995 surges and a small
advance in the northern part of the marginal zone
which caused a slight redistribution of the proglacial
drainage at the immediate forefield of the glacier and
the creation of small, episodic lakes.
Acknowledgements
The authors thank professors Emrys R. Phillips and
Ívar Benediktsson for their valuable and insightful re-
views of the article, which led to significant improve-
ments. This research project was financially supported
by a grant from The State Committee for Scientific
Research, No. 2 P04E 045 26.
ÁGRIP
Birtar eru niðurstöður kortlagningar setlaga og land-
forma við norðurjaðar Tungnaárjökuls sem mynduð-
ust í og við jökullón frá lokum litlu ísaldar. Þetta er
fyrsta rannsókn af þessu tagi við jaðar Tungnaárjök-
uls. Landmótunarumhverfi voru túlkuð á grunni set-
lagagreininga. Strandlínur, lítil brimþrep, gamlar ár-
keilur og sethjallar tengjast gömlum jökullónum. Jök-
ullónin mynduðust við norðvesturjaðar Tungnaárjök-
uls er hann stíflaði útfallið við Jökulgrindur. Gömul
kort og loftmyndir benda til að myndun lónanna megi
rekja til framhlaups jökulsins 1945.
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JÖKULL No. 66, 2016 67