Jökull - 01.12.1976, Síða 44

may drain suddenly through superglacial chan-
nels which water is able to melt into the ice
barrier (Schytt, 1956). A variety of glacier-
margin lakes has been described, for example
by Thorarinsson 1939, Liestöl 1956, Stone 1963,
Marcus 1960, Maag 1969, Post and. Mayo 1973,
and classified as to the manner of formation
and various geomorphological settings such as
whether the rock barrier is a mountain wall, a
nunatak, a moraine, and whether the lake is
situated in a ravine, a tributary or a main val-
ley.
Fig. 2 shows the position of the glacier-margin
lakes in Iceland which are known to the author.
The lakes are listed in Table 1. Most of the
lakes are found along the southern to the east-
ern edge of Vatnajökull from Skeidarárjökull
to Eyjabakkajökull. The topography in this
area is shaped by two effects which favour the
formation of marginal lakes. The Tertiary
Basalt Formation in this area has a NE-SW
tectonic lineation. But during the last Ice Age
Fig. 2. Glacier lakes in Iceland. The arrows point to tlie locations of the lakes. The numbers
and the letters refer to Table 1.
Mynd 2. Kort, sem sýnir legu helstu jökullóna á Islandi. Tölur og bókstafir vísa til Töflu 1.
42 JÖKULL 26. ÁR
pression. Subglacial water reservoirs of the latter
type are found at geothermal and volcanic
areas. (Björnsson, 1975). Three examples of
such reservoirs are illustrated in Fig. 1 a, c
and e.
The basic theory which has been recapitulat-
ed above applies also for marginal and supra-
glacial lakes. Such lakes are special cases of the
reservoir type in Fig. la.
GLACIER-MARGIN LAKES
Fig. Id shows a general cross-section of a
glacier-margin lake. The lake is bound by gla-
cier ice on one side and rock on the other.
The glacier surface slopes toward the lake whicli
accumulates meltwater from the glacier and run-
off from the surrounding rocks. The lake may
drain either continuously over a col at the rock
barrier or suddenly in a jökulhlaup beneath
the glacier. However, glacier-margin lakes that
form during the summer at subpolar glaciers