Jökull - 01.12.1970, Blaðsíða 32

1904: Sheets 87 and 97; 1:100,000 Danish Geo-
daetic Institute.
1945: Dept. of Geography, University of Glas-
gow, photogrammetric map, 1:15,000
(Welch 1967, Howarth 1968).
1951: Durham University Exploration Society
plane-table map, 1:25,000.
1965: Dept. of Geography, University of Glas-
gow, photogrammetric map, 1:15,000
(Welch 1967, Howarth 1968).
The aerial photographic coverage of the area
is as follows:—
ships of certain channels beyond the outermost
moraine and the moraine ridges suggest that
the moraines actually blocked off the proximal
ends of some channels because the channels
disappear beneath the moraines.
The first cartographic evidence of conditions
in the proglacial area is provided by the Dan-
ish Geodaetic Survey Map of 1904 (Fig. 3).
East of the Jökulsá this map shows only four
sreams draining directly from the ice front
whereas the present morphological evidence in-
dicates that there were many streams draining
the eastern half of the glacier at this time,
Date
August 1945
July 1960
July 1961
June 1964
Sept. 1964
Aug. 1965
Camera/lens
15 cm Metrogon
15 cm Metrogon
15 cm Metrogon
RC-5. 11.5 cm Aviogon
RC-5. 11.5 cm Aviogon
RC-5 11.5 cm Aviogon
Approx. scales
1:46,000
1:36,000
1:37,000
1:40,000
1:30,000
1:15,000
Source
U. S.A., Dept., of Defence
Landmælingar íslands
» >>
Glasgow University
The evidence obtained from these maps and
aerial photographs along with information ob-
tained from Mr. Flosi Björnsson and from field-
work by the authors, was used to construct a
series of maps at 1:30,000 scale. These maps
were subsequently reduced photographically to
produce figures 3—9.
THE EVOLUTION
OF THE DRAINAGE SYSTEM
1890-1904 (Fig. 3)
Prior to the formation of the moraines, pro-
duced at or near the maximum extent of
Breidamerkurjökull in the late nineteenth cen-
tury, streams draining directly from the ice
front built up deposits on the sandur surface.
As soon as moraines began to form, some of
these direct draining channels were blocked
while other drainage channels were maintained
and actually cut through moraine ridges. It
must be remembered that stream flow in a
glacial environment is variable and at times
much of the sandur beyond the moraine system
would have been covered by anastomosing
stream systems while at other times drainage
would have been limited to certain of the
main channels. The morphological relation-
30 JÖKULL 20. ÁR
particularly east of stream 8. These streams
may not have been recorded on the 1904 map
either because of their comparatively small size
or because they were not actually flowing when
the ground survey was carried out.
In 1904 the Jökulsá consisted of a series of
braided channels forming a stream system
never less then 500 m wide. Streams 16 and 18
issued from the same point at the ice edge
before they diverged and flowed into the
Vestri-Stemma. Between streams 16 and 8 three
moraine ridges had been produced by 1904.
West of the Jökulsá eight streams drained
directly from the ice front. Some of these are
shown to have relatively simple courses while
others are depicted as typical anastomosing
stream channels. It is interesting to note that
channels 43, 45, 49 and 51 had already been
established by 1904 and continued to carry the
bulk of the meltwaters draining from the west-
ern half of the glacier.
1904-1931 (37)
Data for the whole area for either 1931 or
1937 is not available so one map based on in-
formation pertaining to 1931 for the eastern
half and 1937 for the western half of the area,
has been constructed. On the scale of repro-