Jökull - 01.12.1986, Blaðsíða 84

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An estimation of glacial run-off and mass balance for
Tungnaárjökull and Brúarjökull, Iceland
ARI TRAUSTI GUÐMUNDSSON
Menntaskólinn við Sund
104 Reykjavík
SUMMARY
An attempt is made to estimate the glacier com-
ponent in rivers draining two outlet glaciers from the
Vatnajökull ice-cap, i.e. Tungnaárjökull (121 km2)
and Brúarjökull (approx. 1300 km2). An estimation of
the mass balance of the glaciers is also attempted.
Principial sources of data are records of annual pre-
cipitation from weather stations and discharge
records. A set of profile measurements on Tungnaár-
jökull is used for calculations for the smaller glacier.
The period 1961 — 1982 was considered for
Tungnaárjökull and the river Tungnaá. The estimated
negative mass balance for the glacier is approx. 320
Gl/a in 1961 — 1967 and decreases to approx. 140
Gl/a in the beginning of the 80’ies. From 1968 and
onwards the annual discharge of Tungnaá tends to de-
crease which can partly be explained by diminishing
glacial run-off. It amounts to 647 Gl/a in 1961 — 1967
but to 450 Gl/a in 1976-1979 or 24,3% and 17,3%
of the mean annual discharge of Tungnaá, referred to
the gauging station at Vatnaöldur.
The volume of Tungnaárjökull was reduced in the
period considered by 4.5 km3. Around 1980, radio
echo-soundings yielded 36 km3 for the volume of
Tungnaárjökull.
The period 1971 — 1982 was considered for Brúar-
jökull and the rivers Kreppa and Jökuls á Brú. The
glacial run-off is estimated to vary between 3945 Gl/a
in 1971-1976 and 3425 Gl/a in 1980-1982. Since
the annual discharge of both rivers decreases at the
same time, the glacial component remains more or
less steady around % of the total discharge, referred to
the gauging stations some 40 km from the terminus.
A rough estimate of the glacier-volume reduction
gives 12.6 km3 for 1971-1982 or 1050 Gl/a. The
total volume is unknown.
The results from the calculations have large error
limits; up to tens of percent. It is not possible to calcu-
late the error limits since most components have
either unknown error limits or are based on estimates.
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