Jökull - 01.12.1988, Blaðsíða 26

incorrectly assumed these moraines to be Little Ice
Age features, dating from 1870 (as at Svínafells-
jökull), despite the fact that corresponding lichen
measurements were anomalously small, falling well
below the general calibration curve. The present
view, that the moraines are more recent features dat-
ing from about 1904, is thought to be a more accu-
rate interpretation, supported by both cartographic
and lichenometric evidence (Table 1).
At Svínafellsjökull, the 1904 position is found on
the proximal side of the earlier Neoglacial limits,
and in many places has been obscured by more
recent readvances of the snout (Fig. 5).
After 1904, no further documentary or carto-
graphic evidence is available until 1932, when the
Icelandic Meteorological Office began its annual
measurements. It appears however that the interven-
ing period was one of complex ice-marginal fluctua-
tions: Thorarinsson (1943, p. 47) noted that the
southem Vatnajökull glaciers were generally
affected by three episodes of stagnation or read-
vance during the early part of this century, follow-
ing the strong recession of the 1890s. At Skaftafells-
jökull, three distinct ridges are found on the proxi-
mal side of the 1904 moraine (Fig. 5). Lichen meas-
urements from these ridges yield dates of 1906,
1917 and 1930 respectively (Table 1), when com-
pared with the calibration curve developed from
other, independently dated moraines (Fig. 6 in
Thompson and Jones, 1986). The younger of these
moraines is roughly coincident with the "apparent"
position of the ice front on the 1904 map, lending
further support to the suggestion that this had
merely been the contact between clean and debris-
laden ice at the time of the survey, and did not
become stable enough for permanent lichen coloni-
zation for a further 26 years.
At Svínafellsjökull, the height and complexity of
the "1930" ridge would seem to suggest that here the
three readvances retumed successively to the same
position, building up a composite stmcture of super-
imposed moraines. King and Ives’ (1955) suggestion
that the height of these moraines may be indicative
of an ice core now seems unlikely, as comparison of
the 1945 and 1982 aerial photographs reveals no
significant change in either morphology or elevation
over this 37 year period. From a preliminary inspec-
tion of lichen sizes along this moraine it appears to
have been affected by more recent readvances of this
part of the snout. Such advances may not have
reached the crest of the moraines, but appear to have
reactivated the proximal slopes by oversteepening
(Fig. 4B).
1930 -1945
Both glaciers retreated very rapidly between 1930
and 1945, as indeed did most of the Icelandic gla-
ciers, as a consequence of the marked amelioration
of climate (see Fig. 3B and earlier discussion). Dur-
ing this period the annual records for Skaftafells-
jökull reveal two significant episodes of temporary
readvance (1932-34) or stagnation (1938-39) at dis-
tances of 1300 and 1000 metres (respectively) from
the 1980 snout. Two very well-defined and clearly
separated moraine ridges are found in corresponding
locations in the field (Fig. 5), whilst a third ridge,
which does not appear to be associated with any
major fluctuation of the glacier, is found to
correspond with the snout position on the aerial pho-
tographs of 1945. An additional datum is provided
by the short remnant of medial moraine between
Skaftafellsjökull and the northem tip of Svínafells-
jökull, where the glaciers are known to have
separated in 1935 (Thorarinsson, 1956).
At Svínafellsjökull, the 1945 ridge can again be
identified from the aerial photographs, but between
this and the 1930 crest there are numerous smaller
and discontinuous ridges which cannot easily be
assigned to specific fluctuations of the glacier. This
uncertainty is heightened by the considerable relief
of the morainic topography upon which the ridges
are superimposed, and the consequent irregularity of
both present and former outlines of the glacier
snout.
A well-marked trimline along the southem side of
the valley, (noted by King and Ives, 1955), which
appears to be associated with the high crest of the
"1930" terminal and lateral moraines, serves to indi-
cate the amount of recent downwasting of ice in this
area, whilst a higher and more degraded trimline,
24 JÖKULL, No. 38, 1988