Jökull - 01.12.1973, Blaðsíða 47

Katla and Askja
GUTTORMUR S I GBJARNARSON
NATIONAL ENERGY AUTHORITY, REYKJAVÍK, ICELAND
ABSTRACT
A parallel is drawn between Katla and Askja,
the idea being put forward that the subsurface
of Mýrdalsjökull is a mature central volcano
with a caldera in the middle, which could be
co?npared to the Askja phenomenon in Dyngju-
fjöll. On the basis of this the volcanic activity
of Mýrdalsjökull should also be related, with
only one eruption at the same volcanic fissure
or vent, as a rule. As a result of this the Katla
jökulhlaup does not always find its way out to
Mýrdalssandur, but can, and actually has,
emptied mto Markarfljót and Jökulsá á Sól-
heimasandi.
what is katla?
In summer 1972 I was staying for some weeks
m the Laki area on Síduafréttur. From there
Mýrdalsjökull, with the Katla depression, lies
open before the eye, as shown in Fig. 1. My
attention was increasingly drawn to various
shadows on the snow field, varying incessantly
in relation to the position of the sun. The scene
reminded me of the Dyngjufjöll massif and
Askja caldera which I had also observed for
some weeks. What would they look like if a
similar ice cover to that of Mýrdalsjökull was
put on top of them? Since then I have examin-
ed all the available studies of the Katla and
Askja areas. There are so many similarities be-
tween the two that I have been convinced of
their relationship. According to this proposition
Mýrdalsjökull is resting on a mature central
volcano with a large caldera as generally ac-
cepted by Icelandic geologists. The eruptions
in Katla are, therefore, probably most identical
to the eruptions in Askja where, as a rule, there
only occurs a single eruption at each vent. The
Fig. 1.
View towards Mýrdals-
jökull from the summit
of Mount Laki, the crater
row is in the foreground.
The outlet glacier farth-
est to the left is Höfda-
brekkujökull. The Katla
trougli is situated at the
head of it. The wide de-
pression in the central
part of Mýrdalsjökull
should be visible.
Mynd 1.
Mýrdalsjökull séður frá
Laka. Gígaröðin er i for-
grunni. Höfðabrekku-
jökull lengst til vinstri.
Kötlulægðin er við upp-
Ý L b / i r, m n P i J.. 7 ‘V i i ' A’
‘sotlulœgðm er við upp-
tök hans. Stór lœgð ætti að sjást i miðjum Mýrdalsjökli
JÖKULL 23. ÁR 45