Jökull - 01.12.1971, Síða 23

gravimetric method described earlier in this
paper. The maximum value of the contribu-
tion of the storage change in the area between
the glacier terminus and the limnigraph was
estimated to be í 0.2 ■ 10° m3.
Table 7 shows a comparison between the
terms in the water balance equation calculated
separately for the whole basin ancl for the
glacier itelf. It appears that the measured run-
off is definitely higher than the sum of pre-
cipitation and the glacier melt. The error in
R can be assumed to be less than 5 percent
and even if one assumes the error in AS to be
10 percent one must conclude that P has been
underestimated during the period. Better values
for the average precipitation could have been
obtained by establishing a precipitation-eleva-
tion correlation and by subjective drawing of
isolines of precipitation. The given values are
however meant to demonstrate the difficulty
of precipitation measurements. The measured
values of R and AS indicate that the precipita-
tion contributed about one third of the run-
off but only about one fifth of this precipita-
tion was measured in the present case. This
can further be underlined by the fact that the
hydrological method would have overestimated
the glacier storage change to 1.35 times the
value given by the stratigraphic method.
SUMMARY
On the small glaciers in Mid-North Iceland
the climate is clearly dominated by the advec-
tive factors. Data from the permanent weather
stations in the area could therefore be used
to describe the mass balance on the glaciers.
Continued meteorological and glaciological ob-
servations on the glaciers are, however, necess-
ary for at least one decade, if existing climatic
observations are to give a quantitative stati-
stical measure for past mass balance variations.
Such glacial-meteorological studies should also
examine the importance of the proximity of
the sea for the nourishment and ablation of
the numerous glaciers in the area.
At present, data for only two years from
Bægisárjökull are available. An attempt can be
made to use these data to interprete qualita-
tively past mass balances from the simple re-
presentation of observations given in Fig. 3
from Akureyri. Fortunately these two years give
some hints on the conditions for zero net
balance for the glacier, the first year having a
positive net balance and the second one a zero
net balance. The marked difference between
the winter accumulation and ablation in these
two years shows also how sensitive the summer
ablation is to small changes in the mean air
temperature. As a guiding rule it might be
suggested that if the mean air temperature for
the five months May to September at Akur-
eyri falls below 8° C after a winter with
normal precipitation then Bægisárjökull is
growing. Taking the two years 1966—67 ancl
1967— 68 as a guide, the data in Fig. 3 can
then be interpreted as follows. For the years
from 1930 to 1950 Bægisárjökull seerns to have
had a negative net mass balance except for
1937—38 and 1942—43. After 1950 the magni-
tude of the net balance becomes more variable.
Every second year from 1951—52 to 1957—58
the net balance could have been positive or
zero, and after years with a negative balance
until 1961—62, all years up to present except
1968— 69, the net balance has been close to
zero or positive.
Bægisárjökull has shown a general recession
since measurements started in 1924 but with
slower rate in the last years.Its existence, nou-
rished by the neighbouring mountains and
maintained by its facing to north, has been
secured all these years since the equilbrium
line has on the average been below 1150 m
a. s. 1. If the trend of cooler summers shown
in Fig. 3 continues, only normal winter pre-
cipitation is needed to obtain positive net
balance. This temperature trend is likely to be
most prominent in the northern part of Ice-
land and the many small glaciers in the area
will then give an excellent opportunity to
study the glacier response to mass balance
variations.
ACKNOWLEDGEMENTS
Thanks are due to Jóhann Sigurjónsson for
the cooperation on the glacier. To liim and
Olav Liestýl of the Nonaegian Polar Institute
I am indebted for valuable discussions; to Sig-
urjón Rist of the National Energy Authority,
JÖKULL 21. ÁR 21