Jökull - 01.12.1988, Blaðsíða 28

has continued to decay, with the moraines eventu-
ally becoming stabilized between 1968 and 1980.
PROGLACIAL LAKES
The final stages in the disintegration of a large
part of the dead-ice area described above, resulted in
the formation, since about 1968, of a temporary ice-
marginal lake at the extreme southem tip of Svína-
fellsjökull (Fig. 2). A substantial part of the meltwa-
ter contributing to the Svínafellsá now drains
through this lake, which as a consequence is being
rapidly infilled by the trapped sediment. Three other
lakes, occupying deep depressions enclosed by
moraine ridges and backed by ice cliffs (Fig. 5)
appear to be more permanent features of the Svína-
fellsjökull ice-front, having relatively limited
sources of sediment input. The largest of these has
been in existence since at least 1945, and was prob-
ably first revealed as the ice began its rapid retreat
from the "1930" crest of the high moraines.
At Skaftafellsjökull, a large number of lakes were
uncovered by the intermittent retreat of the ice from
1940 onwards. As at Svínafellsjökull, most of these
lakes correspond to the former positions of project-
ing lobes of ice from the scalloped edge of the gla-
cier tongue, as seen in many of the aerial photo-
graphs (Fig. 2) and in the planform of the enclosing
moraine ridges (Fig. 5). Such depressions were
probably formed either by direct glacial erosion dur-
ing the short-lived episodes of readvance, or by the
scouring effects of meltwater emerging from
beneath the glacier under hydrostatic pressure (Arn-
borg, 1955, p. 226; Howarth and Price, 1969).
By either mechanism, the formation of such prog-
lacial lakes is most likely to occur during the
advance or stagnation of the glacier snout. This
notion is supported by the fact that very few lakes
were formed during the rapid and almost continuous
retreat of Skaftafellsjökull between 1934 and 1940.
Boulton et al. (1982) have reported evidence to sug-
gest that the major proglacial lake basins at
Breiðamerkurjökull were excavated by the glacier
during the main Little Ice Age advance, becoming
exposed after 1932 as the ice-front retreated.
Kettle-hole lakes, formed by the melting of
stagnant ice beneath outwash sediments, are rarely
encountered in association with the steep valley gla-
ciers of Öræfi, though they have been widely
reported from the from the proglacial areas of
nearby Vatnajökull outlet glaciers such as
Breiðamerkurjökull and Skeiðarárjökull (Price,
1969, Jewtuchowicz, 1973). The latter are character-
ized by extensive supraglacial outwash deposition in
association with rapid frontal retreat, in marked con-
trast with the slower and intermittent recession of
the Öræfajökull glaciers.
At Skaftafellsj ökull, which in many respects is
intermediate between the Vatnajökull and
Öræfajökull outlet glaciers, both in character and
location, there has been a limited development of
kettle hole lakes (between 1960 and 1975) on the
abandoned sandur area adjacent to the eastem
branch of the Skaftafellsá (Fig. 5).
DEVELOPMENT OF THE
DRAINAGE SYSTEM
The drainage pattem of the Svínafellsj ökull and
Skaftafellsj ökull proglacial areas has evolved during
the historical retreat of the two glaciers from their
Neoglacial maxima (c. 1870), and has been inti-
mately associated with the development of moraines
and proglacial lakes (Fig. 2).
The present Skaftafellsjökull ice-front is drained
by two major meltwater rivers, flowing in complex
braided pattems from the eastem and westem
comers of the glacier snout (Fig. 5). These follow
courses which are largely parallel to the ice-margin,
confined for the most part between arcuate
moraines, before uniting as the powerful single-
thread channel of the Skaftafellsá, which cuts
through the outermost moraines.
By contrast, the four major meltwater streams
draining the Svínafellsjökull ice-front form a radial
pattem cutting through the Svínafell moraines,
although the present course of the most northerly
stream (the Neskvísl) is confined between two paral-
lel ridges of the Skaftafellsj ökull moraines.
Throughout the area shown on Fig. 5 it is possible
to recognize a number of stages in the development
of these drainage pattems, in the form of abandoned
26 JÖKULL, No. 38, 1988