Fróðskaparrit - 01.01.1998, Blaðsíða 313

319
Climate Induced Twentieth-Century Glacier
Fluctuations in Southeast Iceland
Veðurlagselvdar jøkulbroytingar í tjúgundu øld á Suðurlandinum
s
í Islandi
Tom Bradwell
Department of Geography, Drummond Street, The University of Edinburgh, Edinburgh, UK, EH8 9XP.
Phone: +44 131 650 1000, Fax: +44 131 650 2524, e-mail: tb@geo.ed.ac.uk
Úrtak
I hesi grein verður kannað sambandið millum, hvussu
Virkisjokull-Falljokull, ein ósajøkul úr Oræfajðkulli í
Islandi, tekur seg aftur, og broytingar í miðallufttemper-
aturi. Jøkulmarkið er broytt tey seinastu 120 árini. Har
sum ísurin er bráðnaður, er eitt vítt øki við proglasialum
strandarlendi. Stakir arcuate kambar og ‘ósløtt’ avlætt-
ingingarmorena eru varðveitt á strandarlendinum og
endurspegla mynstur á tí ójavna fremsta partinum av ís-
inum. Við at brúka likenometriskt tilfar og geomorfisk
sambond á staðnum hevur borið til at gera rættiliga
neyvar relativar tíðarfestingar. Søguligar heimildir og
loftmyndir hava verið brúkt fyri at staðfesta tíðarrøðina
seinnu helvt av øldini. Jøkulin hevur ikki tikið seg aftur
á ein samlíkan hátt síðan endan á kalda skeiðnum nevnt
‘tann lítla ístíðin’. Afturtøkan av tí fremsta á ísinum hev-
ur verið órógvað av re-advance events á ymiskum stig-
um. Eitt uppskot hevur verið, at mynstrið á broytingun-
um av ísmarkinum samsvarar við gongdina í miðalluft-
temperaturi í fleiri ár. Heitari tíðarskeið høvdu við sær
skjóta lækking í 1900-árunum, 1940-árunum og 1970-
árunum; kaldari skeið høvdu ábyrgdina av re-advances
í 1920-árunum, 1950-árunum og seint í 1970-árunum.
Tað sæst, at reaktiónin hjá ísmarkinum til temperatur-
broytingar er seinkað umleið sjey til níggju ár.
Abstract
This paper examines the link between the recession of
Virkisjokull-Falljókull, an outlet glacier from the Orae-
fajokull ice-cap in Iceland, and variations in mean air
temperature. The glacier margin has fluctuated in re-
sponse to climatic change over the past one-hundred and
twenty years. Recession of the ice has revealed an ex-
tensive area of proglacial foreland. Discrete, arcuate
ridges and ‘hummocky’ ablation moraine are preserved
on the foreland reflecting the pattem of ice-front fluctu-
ations. Approximate relative dating of these features has
been achieved using lichenometric data combined with
geomorphic relationships observed in the field. Histori-
cal documentation and aerial photography have been
used to construct the chronology for the latter half of the
century. The glacier has not retreated in a uniform man-
ner since the end of the ‘Little Ice Age’ cold phase. Re-
cession of the ice-front has been interrupted by re-ad-
vance events on various scales. It is suggested that the
twentieth century pattem of ice-marginal fluctuations
corresponds with multi-annual trends of mean air tem-
perature. Warmer periods resulting in rapid recession
during the 1900’s, 1940’s and early 1970’s; colder
spells being responsible for re-advances in the 1920’s,
1950’s and mid to late 1970’s. A lag in the response of
the ice margin to temperature variation is seen to be ap-
proximately seven to nine years.
Introduction
This study employs documentary, carto-
graphic, photographic, lichenometric and
geomorphological evidence to chronicle
the fluctuation of a temperate valley glacier
and examine the relationship between
frontal movements and local climatic con-
ditions.
Iceland is a uniquely important location
for the study of glacial fluctuations owing
Fróðskaparrit 46. bók 1998: 319-332