Jökull - 01.12.1967, Page 40

melt water drains has been carried out. By far
the greatest of these rivers is Ölfusá with the
average discharge of 385 m3/sec (Rist 1956).
Ölfusá receives the most part of its discharge
from Hvítá, Tungufljót, Brúará and Sog, but
TABLE VI
The net ablation on Hasafellsiökull Eystri
1938-1945
Elevation Net ablation
m 106 m3/km2
440-500 96.1
500-600 67.4
600-700 30.1
700-800 8.1
800-900 11.0
900-1000 7.3
1000-1100 7.0
1100-1200 5.8
1200-1300 2.3
1300-1400 0
all these rivers get a part of their water flow
from Langjökull. Other rivers draining Lang-
jökull are Hvitá in Borgarfjördur (90 m3/sec)
and Blanda (55 m3/sec), which receives just a
small part of its discharge from Langjökull.
The total average discharge of these rivers is
about 530 m3/sec. The average discharge of
Tungufljót, which drains the Hagavatn area
(Fig. 7) is about 50 m3/sec and it is the only
one of these rivers, for which the effect of the
ice recession can be calculated separately. For
the other rivers the increase in discharge be-
cause of the recession of Langjökull must be
calculated as a whole. The increase of discharge
due to the ice recession is shown in Table VIII.
The specific weight of the glacier ice was as-
sumed to be 0.9 in these calculations.
About 35% of the Tungufljót drainage area
is covered by the glacier but Langjökull covers
only about 11% of the drainage area, which
is included in the discharge measurements of
Ölfusá at Selfoss, Hvítá at Kljáfoss ancl Blanda
at Gudlaugsstadir. It is therefore quite normal
TABLE VII
The recession of Langjökull and its outlet glaciers, the Tungufljól Drainage Area
and Hagafellsjökull Eyslri
Aver. thinn- Aver. thinn-
ing pr. year ing pr. year
Decrease in volume in cm water Decrease in volume in cm vvater
106 m3 106 m3/year equivalent 106 m3 106 m3/year cquivalent
1922-1938 1938-1945
Hagafellsjökull Eystri . ~ 2000 125 ~ 100 1316 188 161
Tungufljót Drainage Area . .. . ~ 4200 263 ~ 80 3220 460 150
Langjökull . ~ 10000 625 ~ 54 7919 1131 101
1945-1966 1890-1966
Hagafellsjökull Eystri 2017 96 94 5623 74 65
Tungufljót Drainage Area . .. 4490 214 76 12529 165 55
Langjökull 11040 526 50 30838 406 37
TABLE VIII
The increase in tlie discharge of glacial rivers clue to tlie glacial recession
1922-1938 1938-1945 1945-1966 1922- -1966
% of aver. m3 / sec discharge % of aver. m3/sec discharge % of aver. m3 / sec discharge m3/sec % of aver. discharge
Tungufljót 7.5 15.0 13.1 26.2 6.1 12.2 7.7 15.4
Ölfusá -f Hvítá -f Blanda . .. . 17.8 3.4 32.3 6.1 15.0 2.9 18.8 3.5
274 JÖKULL 17. ÁR