Jökull - 01.12.1967, Blaðsíða 37

Hagafellsjökull Eystri
Tungufljót drainage area on Langjökull
Langjökull as a whole.
The retreat of Hagafellsjökull
The retreat of the snouts of Hagafellsjökull
Eystri and Hagafellsjökull Ytri has been mea-
sured as showed in Table I.
The measurements of the retreat of the gla-
cier snouts seem reliable in most cases, even
though they have not all been performed at
the same place. Because of this there may be
some error from one year to another, but it
will not liave any effect on the retreat as a
whole. The maximum extent of the glacier was
measured from the farthermost of the visible
Fig. 7: Langjökull drawn from the map of
Geodetic Institute. Scale 1:100,000 (surveyed in
1938). The liatched area represents the Tungu-
fljót drainage area on Langjökull. The cross-
hatched part indicates the area, wliich was hyp-
sometrically measured on the maps surveyed in
1938 and 1945 in orcler to calculate the ice
recession. Black indicates the marginal lakes.
Langjökull samkvœmt korti danska herforingja-
ráðsins (mcelt 1938). Vatnasvœði Tungufljóts á
Langjökli er skástrikað. Krossstrikaða svœðið
var sérstaklega mcelt á kortunum frá 1938 og
1943 til þess að reikna út rúmmálsbreytingu
jökulsins. Vötn við jöliuljaðarinn eru sýnd svört
á myndinni.
recent glacial features and the positions of the
ice front in the years 1902 and 1929 were
estimated with reference to the “jökulhlaups”
of these years. In some cases two different mea-
surements of the retreat for the same space of
time were available, but in all cases the differ-
ence proved to be less than 25 m. The rate of
the retreat of the glacier lobes has been differ-
ent from one year to another, but the average
over 10—12 years has been very constant, except
for Hagafellsjökull Ytri, which has retreated at
a double rate in the last decade. According to
historical data and also in good agreement with
temperature records (Eythórsson 1931 ancl 1949,
líergthórsson 1967) the glaciers did not begin
to retreat to any degree until after 1920. Table
II gives the average retreat for 10—12 years
periods after 1922, which, with reference to
temperature records, I have chosen as the first
year in the warmer climatic epoch of this cen-
tury.
The changes in the area of the glacier have
been obtained by measuring its size on the
maps. Table III shows the area of the glacier
lobe, which is shown on Fig. I, as it proved
to be at different times.
The area of the glacier in 1966 is not mea-
surecl but calculated on the assumption that
the clecrease in the area has been proportional
to the retreat of the glacier lobe as it hacl
been before 1960 (Liesttþl 1962). The three
selected areas (Fig. 7) were also measured on
the maps from 1938 and 1945. The maximum
extent of Hagafellsjökull Eystri and the glacier
on the Tungufljót drainage area were measured
by the use of aerial photographs, but for Lang-
jökull as a whole such a measurement could
not be performed. The obtained results are
shown on Table IV. The calculated figures are
based on the assumption that the proportion
between the rate of retreat of the glaciers and
the loss in area in these times was the same as
found in periods of observation. According to
these calculations the area of Langjökull has
clecreased about 14% from its maximum extent
and nearly 10% since the year 1938, which is
often used as a reference as to the size of
glaciers in Iceland.
The shrinkage in volume
Hypsometric measurements of Hagafellsjökull
JÖKULL 17. ÁR 271