Jökull - 01.12.1973, Page 50

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Fig. 4. A map of Mýrdalsjökull. The circle in the middle indicates a possible caldera, 10 km
in diameter. The broken lines show the outlines of Askja calderas at the same scale.
Mynd 4. Kort af Mýrdalsjökli. Hringur dreginn um miðju jökulsins táknar líklegt ketilsig,
10 km í þvermál. Brotnar línur sýna ketilsig Oskju i sama mœlikvarða til samanburðar.
ice varied between 200—370 m (Rist, 1967). All
these places were on the top of the snow field,
most of them in the neighbourhood of the
Katla trough. Otherwise, the subsurface is un-
known, except where nunataks protrude
through the ice. However the appearance of
the ice cover and the outlet glaciers give a
certain idea about its topography.
In Fig. 4 is drawn a hypothetical circular
caldera 10 km in diameter which is in good
agreement with, but drawn independently of,
the negative magnetic anomaly mapped there
48 JÖKULL 23. ÁR
recently by Th. Sigurgeirsson (personal com-
munication). It is somewhat larger than Askja,
but smaller than the one in the Landmanna-
laugar area (K. Scemundsson, 1972). The out-
lines of Askja caldera are also drawn in the
figure, revealing that the downthrow in Mýr-
dalsjökull is of a very similar order of magni-
tude to that in Dyngjufjöll, even though it
cannot be expected to be of the same shape or
complexity.
There are many things to support the pro-
position that Mýrdalsjökull is resting on a