Fróðskaparrit - 01.01.1998, Síða 324

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CLIMATE INDUCES TWENTIETH-CENTURY GLACIER FLUCTUATIONS
IN SOUTHEASTICELAND
ent link between falling air temperatures
and glacial expansion. A further explana-
tion may be related to increased precipita-
tion levels during these times of falling
temperature, such as those that were expe-
rienced during the late nineteenth-century
(Eythorsson and Sigtryggsson, 1971). This
is unlikely over such short time periods (1-
10 years) although cannot be ruled out for
some of the longer changes. It can be seen
from this preliminary research that further
work is needed on this topic.
Unfortunately, precipitation records
from the weather station at Fagurholsmyri
are deemed to be unreliable and could
therefore not be used to complement this
work. This is regrettable as variations in
precipitation may partly explain periods of
ice-front advance not seen to correlate di-
rectly with temperature variations, for ex-
ample between 1980 and 1988. However,
this does not detract from the overall rela-
tionship observed between ice-marginal
movement and mean air temperature trends
at Virkisjokull-Falljokull. Further work is
currently examining the exact role of mean
summer temperatures and the length of the
ablation season in forcing ice-margin fluc-
tuations.
Conclusion
The twin valley glacier of Virkisjokull-
Falljokull retreated from its Nineteenth-
Century maximum between 1885 and 1910
AD, with the rate of ice-front retreat being
most rapid during the first five years of the
twentieth century. After a brief positive
fluctuation in the late 1920’s, recession
continued from the mid 1930’s up until
1973. As the climate became cooler after
1960, the retreat of the glacier margin
slowed down and subsequently a period of
advance occurred in the 1970’s and 1980’s.
This observation is in agreement with those
findings of Bjðmsson (1979) and Sigurds-
son (1989) who have evidence from the
majority of glaciers in Iceland. Since about
1985 the climate in Iceland, and on Earth as
a whole, has become warmer. As a direct
consequence of this most recent tempera-
ture rise, Virkisjokull-Falljokull gradually
began retreating again around 1993. Inter-
estingly, allowing for the inferred lag-time
of between 7 and 9 years, Virkisjokull-
Falljokull may continue to retreat indefi-
nitely in response to the warmer conditions
currently being experienced. A qualitative
prediction of this nature, if supported,
could be of great scientific and socio-eco-
nomic value.
In general, it can be concluded that fron-
tal fluctuations of Virkisjokull-Falljokull
have been in sympathy with climatic trends
over the last century. The ice-margin has
shown a relatively coherent, lagged re-
sponse to air temperature variations on a
multi-annual scale over the last one hun-
dred years. A good correlation is seen be-
tween phases of glacial retreat and periods
of elevated local air temperature, particu-
larly between 1920 and 1980. The time lag
between the onset of one such warming
phase and the subsequent glacial recession
is seen to be in the region of 7 to 9 years. A
similar correlation is observed between
phases of glacial advance and periods of
falling or depressed temperature. Although
the response time is of a similar magnitude