Jökull - 01.12.1973, Blaðsíða 6

and the area around Höfn. Although this
ERTS-1 image of Vatnajökull shows the largest
area of the icecap of any image, other ERTS-1
images, acquired at different times, show other
parts of Vatnajökull. Therefore, in the space
of about 8 months, most of the Vatnajökull was
imaged by the multispectral scanner sensors on
the ERTS-1 satellite.
METEOROLOGICAL AND
HYDROLOGICAL FEATURES
From Medallandssandur to Ingólfshöfdi to
the coast opposite the Hali farm, the coastline
can be seen faintly, although the terrain is still
quite dark where no snowfall increases the re-
flectivity of the land. The snowline can be seen
on the upper parts of the snout of Skeidarár-
jökull and on the higher elevations of the
Eldhraun and Medallandssandur areas. The
demarcation line between snow cover and bare
ground reflects the air temperature on 31
January 1973 and also represents the 0°C iso-
therm relative to elevation after a recent heavy
snowfall. Two weather stations in the Icelandic
Weather Bureau network fall within the area
of the image, Kirkjubæjarklaustur and Fagur-
hólsmýri, 45 km southwest and 30 km south-
east of Skeidarárjökull, respectively.
Weather records from the Icelandic Weather
Bureau show that both Kirkjubæjarklaustur and
Fagurhólsmýri experienced heavy precipitation
(26.2 mm and 27.2 mm, respectively) in the
form of rain on 29 and 30 January 1973. Such
precipitation would increase in amount at
higher elevations and be in the form of snow.
The weather turned colder at both stations
after passage of the storm. At Kirkjubæjar-
klaustur the air temperature was — 3° C at
the time of satellite passage on 31 January
1973 (Sigtryggsson, H., 1973, personal commun-
ication).
The lack of snow cover on the snout of
Skeidarárjökull indicates that this glacier is
ablating to some degree in midwinter, dur-
ing the coldest montli of the year. The same
probably holds true of the snout of Skafta-
fellsjökull, Svínafellsjökull, and Breidamerkur-
jökull, although it is difficult to tell because
of the darkness and cloudiness at the loca-
tion of the latter. According to Eythorsson
4 JÖKULL 23. ÁR
and Sigtryggsson (1971), for the period 1931—
1960 the average temperature isotherms for
January in this part of Iceland are 0° C for
the coastline and — 1 ° C for the southern
margin of the Vatnajökull. [The mean tem-
perature (1931—1960) for January for Kirkju-
bæjarklaustur and Fagurhólsmýri is — 0.4° C
and 0° C, respectively]. Although botli weather
stations have the 3rd and 2nd highest mean
annual precipitation (1931—1960) of weather
stations in Iceland, 1725 mm and 1761 mm for
Kirkjubæjarklaustur and Fagurhólsmýri, respec-
tively, they are also subject to frequent thaws
because of their proximity to the warmer ocean
waters to the south. For the period 1931—1960,
for two-thirds of the month of January Fagur-
hólsmýri lacked a measurable snow cover.
The three largest fresh-water lakes in the
image are frozen and snow-covered: Thóris-
vatn, Langisjór, and Grænalón. The position
of the glaciers on the western and eastern part
of Grænalón, particularly the steep edge of the
ice dam on the east, can be clearly seen.
The flat snout of the western glacier tongue
contrasts sharply with the steeper calving front
of the eastern glacier tongue because of its
position in the lake.
Several flowing streams and rivers are evi-
dent in the image including the following:
streams from the snout of Skeidarárjökull, Sand-
gígjukvísl, Skeidará, and Súla; Núpsá, Skaftá,
Djúpá, Hverfisfljót, and Hólmsá and north of
Vatnajökull, Jökulsá á Fjöllum. It would seem
that a study of ERTS-1 imagery of Iceland
during the late winter and early spring, parti-
cularly whether or not rivers are flowing or
frozen, can give a qualitative measure of the
climate in the more remote areas of Iceland.
APPEARANCE OF SNOW-COVERED
TERRAIN AND ICE FEATURES
Under the low angle (7°) of solar illumina-
tion the uneven surface of Vatnajökull becomes
strikingly apparent. Every minor irregularity,
depression, nunatak, or other morphologic fea-
ture of the surface of the icecap is strikingly
displayed. How many of the depressions and
higher areas are caused by subglacial topo-
graphy or are structurally controlled and how
many depressions are the result of subglacial