Jökull - 01.12.1970, Síða 34

lakes (Fig. 5), Fjallsárlón, Breidárlón, Jökulsár-
lón, Stemmulón. The evolution and form of
these lakes have been discussed elsewhere (Ho-
wartli and Price 1969) and only their signific-
ance in the development of the drainage systern
will be discussed here.
East of the Jökulsárlón this period represent-
ed fairly rapid retreat of the ice front over
an horizontal distance of approximately 1 km.
The surface exposed during this retreat sloped
in a general south-easterly direction and con-
sisted mainly of fluted ground moraine. A
drainage system developed which was largely
controlled by the fluted surface and these
streams were truncated at their south-easterly
ends by channels developed either in a topo-
graphic low or on the proximal side of a
moraine ridge. These collecting channels (22
and 23) either carried the meltwaters north-
eastwards to the Stemmulón or south westwards
to the Jökulsárlón. The streams indicated on
Fig. 5 varied greatly in size. In some cases
they barely washed the surface, while in other
cases channels up to 60 m in width, but rarely
more than 2 m deep, were cut.
Of particular interest is channel 24. This
channel occupies the drainage divide between
channels cut by streams draining either to the
32 JÖKULL 20. ÁR
west into the Jökulsárlón or to the east into
the Stemmulón. As the glacier retreated across
the fluted surface, this stream maintained its
course. On the 1945 aerial photography, water
could still be seen occupying the channel.
The aerial photography has allowed an ac-
curate representation of the 1945 drainage
system. Behind the moraine ridge shown close
to the ice edge on the eastern half of Fig. 5,
a series of pools developed between the ice
edge and the moraine ridge. Many of these
supplied meltwater to channels on the pro-
glacial surface. In the north-east a small pro-
glacial lake had been formed frorn which a
large stream (3) flowed towards the Stemmulón.
By 1945 the Jökulsá was an important stream
acting as an outlet for the Jökulsárlón. This
outlet actually occupied two parallel channels
but it was the western channel which was to
prove the more significant.
West of the Jökulsárlón three streams carri-
ed all the meltwaters from the front of Breida-
merkurjökull and Fjallsjökull. Sometime be-
tween 1938 and 1939 channel 45 ceased to
function (personal communication, Mr. Flosi
Björnsson), but with the development of the
Breidárlón, channel 49 continued to act as an
overflow. In 1945 channel 46 and other pro-