Jökull - 01.12.1974, Side 13

Fig. 9. A map of Grímsvötn summarizing data available at present (see Fig. 8). The line ABCDEF
runs along the cross section in Fig. 14. This line includes several cauldrons formed after the
jökulhlaup in 1972. It is suggested that the subglacial route for the jökulhlaups lies close to this
line, see Fig. 10.
Mynd 9. Kort af Grímsvatnasvœðinu, sem sýnir sömu gögn og Mynd 8. Línan ABCDEF liggur
um sigkatla, sem sáust eftir hlaupið 1972. Leið jökulhlaupanna liggur líklega nœrri þessari línu.
subglacial ridge east of Grímsvötn. The suggest-
ed variation of ðb in other parts of the glacier
is not unlikely in the light of the variation of
ðb outside Vatnajökull (Pálmason, 1974; Sig-
urdsson, 1970). A rock face can be seen at 1850
m on the north-west side of Bárdarbunga.
rhis suggests that 8b = — 40 mgal at the very
top of that mountain. No use has been made
of the gravity data south of the map in Fig. 9.
The poor agreement between gravity and seis-
mic data raises some doubt as to whether the
glacier is 1000 m thick in this area (Pálmason,
1964). An ice thickness of 220 m on Grímsvötn
was first suggested by Thorarinsson (1965) on
the basis of yearly geodetic surveys which show-
ed that the central area was constantly 21 m to
22 m above the water level at the edge of the
cover (the profile Depill—Grídarhorn, Fig. 2).
Seismic results can be reinterpreted to support
this hypothesis. The same applies to results of
JÖKULL 24. ÁR 1 1