Jökull - 01.12.1964, Page 29

the average retreat and (c) in 1961/62 3 of 21
measured Vatnajökull outlets were slightly ad-
vancing and 1 was stationary, which is a higher
figure than for any year in the latter half of
the 1950s.
Fig. 13 also shows the annual precipitation
and teinperature at Fagurhólsmýri, south of
Vatnajökull (öræfajökull) 1930—1963. There is
a clear positive correlation between the tem-
perature and the precipitation diagram, tlie
precipitation increasing with temperature, but
the correlation between these diagrams and the
glacier-variation diagram is more obscure, which
is only what could be expected, as increased
temperature and precipitation have opposite
effect on the glacier regime.
The Swedish-Icelandic Vatnajökull-investiga-
tions 1936/38 led to the general conclusion
that the temperature, both in summer and
winter, had a greater effect on the regime of
the southern outlet glaciers of Vatnajökull than
the precipitation (Ahlmann 1939, p. 187). This,
however, need not be true as regards the ac-
cumulation areas as such, and presumably condi-
tions within them play a greater role for the
sudden glacier advances, than conditions within
the ablation areas.
We know still too little about the condi-
Fig. 13. Diagram showing he average of Vatnajökull outlet glaciers and the annual precipita-
tion and temperaturc at Fagurhólsmýri 1930—1963.
JÖKULL 1964
87