Jökull - 01.10.1998, Page 42

Table 2. Mass balance of drainage basins in Vatnajökul, 1991-1992. B„, and b„, = winter balance, Bs and bs = summer balance,
Bn and bn = net balance, ELA = the equilibrium line altitude, AAR = accumulation area ratio. Accuracy 15%.
-Afkoma skriðjökla Vatnajökuls, 1991-1992. Bw og bw er vetrarajkoma, Bs og bs er sumarafkoma, Bn og bn ársafkoma, ELA er
hœð jafnvœgislínu, AAR er hlutfall ákomusvœðis af heildarflatarmáli jökuls. Nákvœmni 15%.
Area km2 K 10‘m3 Bs 106m3 B„ 106m3 bw m a'1 bs maJ b„ ma'1 ELA m AAR
Síðujökull 380 c. 795 c. -605 c. 190 c. 2.09 c. -1.59 c. 0.50 1050 0.65
Tungnaárjökull 308 539 -464 74 1.74 -1.50 0.24 1125 0.65
Köldukvíslarjökull 313 570 -260 310 1.9 C.-.9 c. 1.0 1200 0.65
Dyngjujökull 1040 2160 c. -450 c.1710 2.08 C.-.4 c. 1.7 1200 0.75
Grímsvötn 160 c. 440 c. 40 c. 480 c. 2.75 c. 0.25 c. 3.00 - 1.00
found as volumes divided by the glacier drainage area.
The mass balance was calculated over both the ice
and water drainage basins. The summer balance over
the water basin is an estimate of meltwater contribu-
tion to rivers and groundwater storage. This estimate,
however, does not include precipitation that falls as
rain on the glacier or snow which falls and melts dur-
ing the summer. The meltwater contribution is com-
pared with river runoff at streamflow gauges closest
to the glacier. For this comparison, we define the
glaciological year from the start of October to the end
of September and the period draining meltwater from
the glacier during the summer from June through
September. Including May in this summer period,
draining spring melt from the highland, would be
misleading because runoff of glacier melt in May is
delayed due to refreezing during the elimination of
the winter cold wave.
Slush areas were observed during the summer but
no superimposed ice was observed in the autumn on
any of the glaciers.
RESULTS
I. THE MASS BALANCE 1991-1992
The mass balance was monitored in five drainage
Fig. 4. Mass balance measurements 1991-1992. Specific mass balance in m water equivalent, bw: winter balance, bs: summer
balance, bn: annual net balance. Measurements sites marked with "+".
-Afkoma 1991-1992 sem metrar vatns. bw: vetrarafkoma, bs: sumarafkoma, bn: ársafkoma. Mœlistaðir eru merktir með krossi.
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JOKULL, No. 45, 1998