Jökull - 01.12.1975, Page 10

z
Fig. 4. Longitudinal sec-
tion of Skaftárjökull to
illustrate the growth of
water cupola from time
t0 to ti between jökul-
hlaups.
Mynd 4. Langsnið af
Skaftárjökli, sem sýnir
vöxt vatnsbólu milli jök-
ulhlaupa.
x
0 10 20 30 40 50 60 km 70
rises at the same rate as the cupola itself. If all
water drains out of tlie cupola in the jökul-
hlaup, a 100 m deep and about 2 km wide ice
cauldron would be formed in the centre of the
depression. The model is in good correspond-
ance with the observations (Björnsson in pre-
paration).
b) Jökulhlaups from Grímsvötn
The explanation of jökulhlaups from Gríms-
vötn was discussed by Björnsson (1974). Fig. 5
shows a cross-section of the water reservoir, the
water basin and the route of the jökulhlaups.
The water basin slopes from the mountain
Bárdarbunga towards the geothermal area at
Grímsvötn. The mountain Grímsfjall rises up
above the glacier surface at the geothermal area.
The water reservoir does not have the regular
shape of a cupola but lies against the wall of
the mountain. The ice cover- floats as an ice
shelf on the water reservoir. At the mountain
wall the water level coincides with the datum
Fig. 5. Longitudinal sec-
tion of Skeidarárjökull to
illustrate the growth of
Grímsvötn between jökul-
hlaups.
Mynd 5. Langsnið af
Skeiðarárjökli, sem sýnir
hcekkun vatns i Gríms-
vötnum milli hlaupa.
8 JÖKULL 25. ÁR