Jökull - 01.12.1986, Qupperneq 84

Helgi Björnsson (1982a): Drainage Basins on Vatnajök-
ull mapped by Radio Echo Soundings. Nordic
Hydrology 1982:213 -232.
Helgi Björnsson (1982b): Jöklarannsóknir í þágu virkj-
unaraðila (On glacier surveys and hydro-electricity).
Tímarit Verkfræðingafél. íslands 67:44 — 52.
Holtzcherer (1954); Expedition Franco—Islandaise
au Vatnajökull. Resultats des Sondages Seismiques.
Jökull 4: 1 —32.
Kristinn Einarsson (1982a): ísaskil í Vatnajökli (On
ice-divides on Vatnajökull; a report). Greinargerð,
unnin fyrir Vatnsorkudeild Orkustofnunar. 4 pp.
Kristinn Einarsson (1982b): Athuganir á Vatnajökli í
vorferð JÖRFÍ 1980. (An expedition report). Grein-
argerð, Raforkudeild, Orkustofnun. 3 pp.
Jón Eyþórsson (1951): Þykkt Vatnajökuls (The thick-
ness of Vatnajökull). Jökull 1: 1 —6.
Jón Eyþórsson (1964/66): Jöklabreytingar (Glacier
variations). Jökull 14—16.
Sigmundur Freysteinsson (1968): Tungnaárjökull (In
Icelandic). Jökull 18: 371—388.
Sigmundur Freysteinsson (1984): Tungnaárjökull —
Langskurðarmælingar 1959—1979 (On profile sur-
veys). Jökull 34: 131 — 139.
Sigurjón Rist (1952): Snjómælingar á Vatnajökli 27.
mars til 24. apríl 1951. (On accumulation measure-
ments). Jökull 2: 6—7.
Sigurjón Rist (1984): Jöklabreytingar. (Glacier vari-
ations). Jökull 34: 173—179.
Sigurður Thoroddsen (1982): Vatnsafl íslands (The
Hydropower in Jceland). Tímarit Verkfrœð.fél. Is-
lands, 47. No 1—6: 5—16.
Sigurður Þórarinsson (1962): Sudden Advance of
Vatnajökull Outlet-Glaciers 1930—1964. Jökull. 14:
76-89.
Sigurður Þórarinsson (1969): Glacial Surges in Iceland
with Special Reference to the Surges of Brúarjökull.
Can. Journ. of Earth Sciences Vol. 6, No. 4:
875—882.
Vatnasvið íslands (Drainage Basins in Iceland). Orku-
stofnun, Reykjavík 1964. (mimeogr.) 93 pp.
Veðráttan — ársyfirlit (Annual weather report, Met.
Office). Veðurstofa Islands.
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.
82