Fróðskaparrit - 01.01.1998, Síða 320

326
CLIMATEINDUCES TWENTIETH-CENTURY GLACIER FLUCTUATIONS
IN SOUTHEASTICELAND
den by downwasting processes which al-
most certainly affected the surface debris.
Lichenometric data has determined the
age of the prominent moraine systems on
the foreland at Virkisjokull-Falljokull. Ar-
guably the most interesting of these ridges
is ascribed a date of 1928 yet occupies a
more advanced position than some appar-
ently older moraines. This evidence is not
contradictory but points towards the ice
margin re-advancing beyond the 1918 posi-
tion in 1928. The date of moraine formation
is fixed as 1928 although the re-advance
probably began around 1923-4 and ended
abruptly with the marked recession of 1929
and 1930. After the resurgence that culmi-
nated in 1928, the eastern margin retreated
nearly 250 metres in the next 18 years, with
a slight interruption in 1934-6. By 1945,
the date of the first aerial reconnaissance,
the ice margin was approximately halfway
through this period of prolonged recession.
A small still-stand during the previous two
years created a low-elevation ridge that is
just visible in the 1945 photograph. This
feature can be used to aid calibration of the
lichen growth curve.
Recession decreased to zero during the
early 1950’s and in 1952 the glacier ad-
vanced marginally for two whole seasons,
producing a small push moraine. Retreat
continued intermittently during the 1960’s
until in 1969 the ice margin seemed to di-
minish with remarkable rapidity, shifting
up-valley 190m in only four years (maxi-
mum rate = -70m/yr). In 1973 the ice mar-
gin was at its most retarded position since
at least 1830 AD and possibly since the
start of the Little Ice Age, over 800 years
ago (Thorarinsson, 1943). Any geomor-
phological trace of the ice margin’s former
position has since been obliterated by sub-
sequent re-advances.
The recession history of Virkisjokull
Falljokull does bear remarkable resem
blance to the local climatic record, repre-
sented by a 5 year-running temperature
mean. The fluctuations of the glacier mar-
gin although seemingly similar to the air
temperature record are not statistically sig-
nificant if unsupported. In order to prove a
causal link, further studies must be carried
out on glaciers in the area. If other nearby
valley glacier margins could be shown to
exhibit sufficiently similar trends to that of
Virkisjokull-Falljokull, the link between
ice and climate could be strengthened.
Measurements of the nearest valley glac-
ier to Virkisjokull, which terminates on a
broad, level outwash plain, have been simi-
larly chronicled since 1932 and extended
using lichenometry back to Í900 AD
(Thompson, 1988). Although there are
small discrepancies between the two, the
retreat history of this glacier, Skaftafell-
sjokull, follows the general pattern dis-
played by Virkisjokull. Marked re-ad-
vances are seen to culminate in 1917, 1930,
1934, 1953 and 1982 at Skaftafellsjokull;
these can be compared with 1918, 1928,
1934, 1954 and 1983 for Virkisjokull-
Falljokull. Similarly, recession is strongest
during the 1940’s and early 1970’s at
Skaftafellsjokull, with the minimum front
position being recorded in 1973.
Discussion
It is possible to demonstrate the general,