Jökull - 01.12.1988, Side 20

Fig. 1. Svínafellsjökull and Skaftafellsjökull: accu-
mulation areas and outlet glaciers. Inset: general
location map of study area.
Mynd 1. Svínafellsjökull og Skaftafellsj ökull og
ákomusvœði þeirra.
from the sub-Atlantic phase of glacier expansion,
which began some 2500 years ago (Thorarinsson,
1956).
On the proximal side of Stóralda, a series of low,
degraded moraines mark the limits of the more
recent "Little Ice Age" advance of the 17th to 19th
centuries, dating from about 1870 (Thorarinsson,
1956). At Skaftafellsjökull, the outermost moraines
are more recent features, dating from about 1904
(see below), and may not represent the true limits of
the Little Ice Age advance. They are probably rem-
nants of a once more extensive series of moraines,
which have been largely destroyed or buried by sub-
sequent outwash activity associated with jökul-
hlaups from Skeiðarárjökull. Since at least 1904,
both glaciers have been generally retreating towards
their present positions, leaving a series of arcuate
recessional moraines.
Stages in the recession of the two glaciers are
recorded in published maps of 1904, 1945 and 1982
and in aerial photographs of 1945, 1954, 1960, 1968,
1975, 1980 and 1982 (Fig. 2). Since 1932, measure-
ments of the ice-front positions have been made on
an annual basis by the Icelandic Meteorological
Office and later by the Iceland Glaciological Society
(.Eythorsson, 1963; UNESCO, 1967, 1973, 1977;
Rist, 1976-1985). These measurements, together
with more qualitative evidence for earlier years
compiled by Thorarinsson (1943), enable a detailed
picture of historical change to be obtained, and per-
mit the identification of episodes of stagnation or
readvance within the overall pattem of retreat,
which in tum may be correlated with the formation
of many of the moraine ridges (Fig. 3A).
The recession curves for both Svínafellsjökull and
Skaftafellsjökull (Fig. 3A) show that rates of retreat
have generally declined from a maximum during the
1930s, to a minimum during the early 1970s, since
when both glaciers have been undergoing a major
episode of readvance, retuming to within a short dis-
tance of their mid 1960s positions by 1984. This
general pattem appears to be characteristic of many
Icelandic glaciers during this period (Jóhannesson,
1986), and is largely a reflection of recent trends of
climatic change, particularly the general fall in tem-
perature since the "climatic optimum" of the 1930s
and 40s. Long-term meteorological records for
Fagurhólsmýri, some 15 km southeast of Svínafell,
confirm this general trend (Fig. 3B), showing a dis-
tinct warm period from about 1926 to 1946 (corre-
lating with the period of maximum rates of reces-
sion), followed by a general reduction in tempera-
tures, particularly after 1964.
Such a close association implies that the glacier
fluctuations are largely a direct response to varia-
tions in temperature, reflecting changes in the rate of
ablation at the snout, rather than the product of more
complex mass-balance adjustments. The latter
undoubtedly occur, but are diffused and delayed by
passing through the glacier system. Such adjust-
ments may be important in controlling the
18 JÖKULL, No. 38, 1988