Jökull - 01.12.1970, Side 37

lake system which would dominate the drain-
age system east of Mávabyggdarönd during the
next five years, could be seen. 1961 was the
last year that channel 43 is known to have
carried meltwaters. After that date all the
drainage was directed either to the Fjallsá or
the Jökulsá.
1960/61-1964 (Fig. 8)
During this period the only significant deve-
lopment in the drainage system was the con-
tinued development of the proglacial lakes as
a result of the retreat of the ice front. By 1964
channel 43 had ceased to function and all the
proglacial drainage from the western half of
the glacier either flowed to the Jökulsárlón or
the Fjallsárlón. At this date the Fjallsárlón was
still divided into two parts by an area covered
with small moraines. East of the Jökulsárlón
all the drainage was concentrated on the
Stemma system.
1964-65 (Fig. 9)
The only drainage changes during this period
relate to channels linking the two parts of the
Fjallsárlón and the upper Stemmulón with a
proglacial lake at the north-eastern end of the
ice front. The change in the Fjallsárlón was
the result of further retreat of the ice front
permitting the development of a channel be-
tween the area of moraine ridges and the ice
cliff. The abandonment of channel 1 was the
result of a fall in the level of the proglacial
lake which fed it. The general lowering of the
surface altitudes of the proglacial lakes in
front of Breidamerkurjökull has been a feature
of the development of the drainage system
since they were formed. The Fjallsárlón dropp-
ed from 16 m in 1945 to 12.5 m in 1965, the
Breidárlón from 31 m to 27.5 m over the same
period and the lakes south of Mávabyggdarönd
from 30 m in 1960 to 20 m in 1965 (Welch
1967, and Welch and Howarth 1968).
CONCLUSIONS
The sequence of drainage evolution describ-
ed above has largely been a function of the
nature of the surface across which Breidamerk-
urjökull and Fjallsjökull have been retreating
and the formation of moraine systems. So long
as the ice front has risen in altitude as it cross-
ed successively higher ground, the southward
flowing drainage was maintained. In some
Fig. 8.
JÖKULL 20. ÁR 35