Jökull - 01.12.1964, Page 20

Fig. 2. The accumulation area of Northern Tungnárjökull E of Hamar. Aerial view towards W,
Oct. 4, 1945. — Photo: S. Sigurdsson.
by Sigurdsson during this flight show network
structure of crevasses all around Kerlingar,
and a very regular fissuring consisting of wide
and very long, somewhat curved and very fresh
looking fissures on the south slope stretching
from Harnar towards ESE (fig. 2). While study-
ing he sudden advances of Brúarjökull and
Sídujökull 1963/64 we learned that this type
of crevassing is typical for the upper part of
the accumulation areas when a sudden advance
is going on or has recently occurred.
Feb. 24, 1946, the present writer joined S.
Sigurdsson on a flight to Grímsvötn (Thorar-
insson Sc Sigurdsson 1947, p. 63). From Reykja-
vík we flew via Thórsmörk and Mt. Laki to
Grænalón, and then towards N short W of
Grænafjall, then E of Thórdarhyrna and Háa-
bunga to Grímsvötn ancl the 1938-caldera N
of the Grímsvötn depression. Frorn there we
flew SSW along the middle of Sídujökull to
the glacier margin. The weather was clear. Our
aim with this flight was to study changes that
might have found place in the Grímsvötn
area since the autumn, but our most interesting
78
discovery during the flight was that both Skaft-
árjökull, and the glacier wliich stretches into
the Langisjór depression, showed every sign
of a recent sudden advance. I cjuote from mv
cliary: “It was astonishing to see how crevassed
the SW part of Vatnajökull was. E of Fögru-
fjöll and NE of Langisjór it has recently ad-
vanced. Its front there is very steep ......
a typical “Vorstossfront”. No frontal moraines
were visible at the front of these glaciers where-
as two series of such moraines were clearly
visible in front of Sídujökull. Sigurdsson esti-
mates the advance to at least 0.5 km”.
An aerial photo of the crevassed glaciers
taken by Sigurdsson was published on p. 17
in Geografiska Annaler, Stockholm 1949, vol-
ume dedicated to H. Ahlmann. The original
is lost, but a similar photo, although not of
the same quality, is published here as fig. 3.
This advance did not affect Sídujökull at all
and there was a sharp limit between its smooth
surface and the crevassed surface of Skaftár-
jökull.
We do not know with certainty when this ad-
JÖKULL 1964