Jökull - 01.12.1974, Page 11

Fig. 7. A map of the present knowledge of the bottom topography of Grímsvötn. The northern
part of the map is uncertain. Contours for the glacier bottom are drawn for 20 m intervals be-
tween 900 m and 1100 m. Contours for the glacier surface are drawn for 20 m intervals between
1460 m and 1640 m, see Fig. 2.
Myncl 7. Kort af botni jöknls við Grimsvötn. Kortið er ónákvœmt norðan vatnanna.
thickness of about 1000 m at the head of the
subglacial Skeidarárjökull valley. This profile
is shown in Fig. 14.
Data
The evidence for this topographical model
will now be presented. The maps in Fig. 6 and
Fig. 7 are drawn on tlie basis of data summariz-
ed in Fig. 8 and Fig. 9 ancl with the help of
the ERTS-1 image in Fig. 10. The Bouguer
anomaly is obtained by using in the Bouguer
correction a constant density of 2.6 g/cm3 for
the whole mass beneath the observation site. By
subtracting the regional Bouguer anomaly (ðb)
an average ice thickness is calculated using a
conversion factor of 14 m/mgal (see e. g. Pálma-
son, 1964).
The glacier surface map differs in some re-
spects from the previously published maps. The
main change is that Bárdarbunga extends about
3 km farther north-east by evidence of Fig. 10.
The 1600 m and 1700 m contours have also
been moved closer to Grímsvötn.
The bottom map is radically changed from
JÖKULL 24. ÁR 9