Jökull - 01.12.1964, Page 25

it had receded 10, 10 and 8 m respectively.
This confirms the conclusion that the advance
had nearly finished before April 23.
The sketch map on fig. 8 is drawn with the
aid. of aerial photos taken by the writer and
M. Jóhannsson. The area affected by the ad-
vance is about 480 km2. There are reasons to
believe that it is nearly exactly the sarne area
as was affected by the 1934 advance, whereas
tlie SW outlets, that advanced 1944, were not
affected this time.
On Sldujökull we observed two main types
of crevassing. One, seen within the accumula-
tion area and mainly N and W of Pálsfjall,
shows very long crevasses, which can be follow-
ed for some kilometers, running nearly parallel
to each other at right angles to the glacier
movement. This type is the same as shown on
fig. 2 from Tungnárjökull 1945. These cre-
vasses become narrower towards the peripheral
parts of the accumulation area.
The other main type is best illustrated by
the photo fig. 9. The ice is split up by a net-
work of crevasses, leaving between them pillars
of ice reminiscent of jointed basalt, although
not so regularly jointed. On relatively flat sur-
faces, like the one shown on the photo, there
is only a small vertical displacement between
the individual pillars. Near the margin, and in
places where the glacier presumably rests on
subglacial hillocks, sorne of the pillars tower
up above the others.
On Sídujökull this network type of crevass-
ing is mainly found within the lower part of
the ablation area. Great areas ol' the glacier
surface showed all sorts of intermediate stages
Fig. 9. The ablation area of Sídujökull WSW of Hágöngur. Aerial view towards N, Sept. 9,
1964. — Photo: S. Thorarinsson.
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