Fróðskaparrit - 01.01.1998, Síða 323

VEÐURLAGSELVDAR JØKULBROYTINGAR í TJÚGUNDU ØLD
Á SUÐURLANDINUM í ÍSLANDI
329
mean when attempting to correlate glacier-
front fluctuations with summer tempera-
tures and winter precipitation in western
Norway. A smoother curve, such as the one
presented in fig.5a, will act to filter out ex-
treme or anomalous values therefore allow-
ing a more representative temperature trend
to be depicted.
Many studies of mass balance in temper-
ate valley glaciers have pointed to the im-
portance of mean air temperature and pre-
cipitation in determining volume changes,
and in turn snout fluctuations (Liestøl,
1967; Hoinkes, 1968; Bjornsson, 1971;
Oerlemans, 1989). This study has concen-
trated on only one of these factors in an at-
tempt to establish the link between ice-
front fluctuations and mean air tempera-
ture. The meteorological data used in this
study is taken from Fagurholsmyri weather
station (lat., 63’50’ N ; long., 16’45’ W) lo-
cated 15 kilometres south-east of the study
site.
If the relationship observed at Virk-
isjðkull, and supported at Skaftafellsjokull,
can be deemed a valid one, interesting op-
portunities are presented for the study of
glaciology and palaeo-climatology. The
possibility of reconstructing former air
temperature trends from known short-term
ice-margin fluctuations becomes a realistic
one. Conversely, knowledge of a long-term
temperature regime may yield important
evidence as to the rates of ice front move-
ment over a similar time period. This study
has highlighted the general, and at times
distinct, correlation between glacial snout
fluctuations and annual air temperature
variability. An important notion to have
emerged from the research is the glacier’s
delayed response to changes in air temper-
ature conditions. Contrary to those views
expressed by Nye (1963a, 1963b) and Lli-
boutry (1971) regarding the response time
of valley glaciers, ice-front fluctuations
ranging from 1 to 200 metres per year are
seen to take effect in less than ten years.
The time-lag observed in this study (7-9
years) is slightly longer than those inferred
previously by Bickerton and Matthews
(1993) [5 years] and Nesje etal., (1995) [3-
4 years] for similar sized Norwegian valley
glaciers. Possible reasons for this small dis-
crepancy may be related to the specifíc
glacier dynamics at Virkisjokull-Falljokull
and, consequently, the sensitivity of the ter-
minus to climatic forcing. However, the ra-
pidity of the response observed at the ice-
front implies that these short-term snout
fluctuations are predominantly a function
of local climatic conditions, in particular
air temperature and precipitation, and not
due to more complex mass balance dynam-
ics travelling through the glacier.
Some difficulty arises when trying to ex-
plain the positive fluctuations or advance
events seen at the study site. These ad-
vances are unlikely to be the result of pure-
ly temperature change. One possible expla-
nation may stem from the fact that the glac-
ier is not in a steady state and has a natural
tendency to advance. A short-term rise in
air temperature would instigate recession
of the ice margin yet falling temperatures
would result in lower melting rates, effec-
tively leading to advance. This relationship
would not interfere with the overall balance
of the glacier yet would explain the appar-