Jökull - 01.12.1956, Page 9

jökull at that time. In all probability Stóralda
is older than tlie settlement of Iceland and its
lack of soil cover at the time of the 1362 erup-
tion can be satisfactorily explained by assum-
ing that soil erosion, caused by the arrival of
man and his livestock, has deprived the rnorai-
nes of their soil cover. In olden times a farm,
Freysnes, was probably situated not far from
Stóralda. Being prehistoric Stóralda must be
formed either after or before the Postglacial
Warm Periocl and in my opinion is was most
likely formed as a result of the climatis deterior-
ation during the first centuries of Subatlantic.
Time, that began ab. 600 B. C.
REDUCTION OF SVÍNAFELLSJÖKULL
AND SKAFTAFELLSJÖIvULL IN RECENT
TIME ACCORDING TO MAPS AND
AERIAL PHOTOS.
The oldest topographical map showing the
margins and contour lines of the glaciers in
question is the Danish General Staff map of
1904, scale 1:50.000 (sheet 87 Öræfajökull SV).
A new map in the same scale was made in 1950
by the U. S. Army Map Service (sheets 6019 III
and 6018 IV). This map is based on aerial
photos taken in Aug. 1945. The height figures
on the glaciers are scanty on the 1904 map.
However there is reason to believe that on this
map and the U. S. Army map the contour lines
are exact enough on the lower part of the
glacier tongues to enable us to calculate their
thinning 1904—1945 with less than 20% error.
On the map fig. 4 the contourlines and river
courses are according to the 1950 map. The
glacier margins 1904 and 1945 are according to
corresponcling topographical maps and so are
the lines showing the glacier thickness on the
longitudinal section fig 5. The dot line showing
the glacier fronts in 1954 is according to the
excellent aerial photos taken by Á. Bödvarsson
Sept. 15, 1954. The dash line showing approxi-
rnately the maximum extension of the glaciers
in historical time is partly based on fielcl
studies and partly on Bödvarssons photos. I
emphasize that this line is only approximate,
especially as regards Skaftafellsjökull and the
northern part of Svínafellsjökull. Nor do we
know at what time the glaciers reached their
maximum extension but a least Svínafellsjök-
ull seems have been very near this stage ab.
1870. At that time the southernmost part of its
front extended so far that blocks of ice broke
off frorn it and rolled down the southern slope
of the outermost moraine ridge N of the Svína-
fell farm. The following figures are based on
the above mentioned comparison between the
1904 and 1950 maps. The figures for the frontal
areal changes are fairly exact but the figures
for the total areal changes are not so reliable
as the mapping of the upper parts of the
glaciers in 1904 can not have been very exact.
Because of the steepness of the uppermost part
of the ablation areas the changes of the 1100
m contours due to thinning of the glaciers since
1904 are negligible.
SKAFTAFELLSJÖKULL.
Area below the 1100 m contour
(approx. firn line) 1904 .... 38.5 km2
Area below the 1100 m con-
tour 1945 ................ 33.0 „
Total areal loss 1904—1945 . . 5.5 „ (14.3%)
Frontal areal loss 1904—1945 4.0 „ (10.4%)
Max. linear recession 1904—
1945 ...................... 1.0 km
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