Jökull - 01.12.1974, Page 21

Fig. 14. ]) A cross section of Vatnajökull along the centre line of the water basin, through
Grímsvötn and down the route of the jökulhlaup. The figure shows the actual case which was
illustrated by the model in Fig. 4. The magnitudes of and P are compared along the route
of the jökulhlaup by plotting p; downward from the water level in Grímsvötn. This is done for
the lowest water level, (hw) min, and the highest one, (hw) max. That illustrates how the po-
tential barrier is reduced as the water level risss in Grímsvötn. Scales are both given in terms
of potential energy heads in meters and as presaire in bars (potential energy per unit volume).
2) A large scale picture of the cross-section from Grímsvötn down the upper part of the route of
the jökulhlaups. The positions of the points on the line ABCDEF in Figs. 9 and 13 are marked.
The seal is broken in an area about 5 km east of Grímsfjall. 3) A large scale cross-section of
the east part of Grímsvötn. P and pj are compared at the end of a jökulhlaup. Then exceeds
P by 5 bars at the eastern edge of Grímsvötn.
Mynd 14. Þversnið af Vatnajökli. Sniðið liggur gegnum vatnasvœði Grímsvatna og þrœðir leið
jökulhlaupanna niður að Skeiðará. Farg jökuls og hugsanlegur vatnsþrýstingur við botn er bor-
inn saman.
JÖKULL 24. ÁR 1 9