Jökull - 01.12.1964, Blaðsíða 27

BRÚARJÖKULL 1963/64
By far the greatest advance of any Vatna-
jökull glacier during the last decade is the
advance of Brúarjökull 1963/64, which affected
about 1400 km2, and brought the margin up
to 8 km forward. The maximum rate of the
advance probably exceeded 4 m per hour. This
advance will be dealt with in a special paper
and it suffice to state that roughly speaking
its culmination seems to have coincided with
that of Sídujökull.
have advanced in this way are of a similar
shape. Their ablation areas are flat and lobe-
shaped, and the intake areas are mostly flat as
well. As far as the subglacial topographv is
known it shows basins of similar type, shal-
low spoon-shaped basins widening towards
the glacier margins. The fact that Sídujökull
and Skaftárjökull move so independent of each
other suggests that their basins are separated
by a NE—SW running subglacial ridge. It is
interesting to note (cf. the photographs in this
TABLE 1
Vatnajöknll glaciers affected by sudden advances
Area Max.
Year Glacier Facing affected. advance
!tm2 km
1963/64 Sídujökull SW 480 about 0.5
Brúarjökull N 1400 „ 8.0
1951 Dyngjujökull N (about 700) ?
1945 Skaftárjökull SW „ 450 „ 0.5
Tungnárjöklar w ?
1934 Sídujökull SW „ 480 „ 0.6
Dyngjujökull N ( „ 700) ?
1890 Brúarjökull N „ 1400 „ 10.0
Eyjabakkajökull NE „ 110 „ 0.6
SOME GENERAL REMARKS
Summing up we find that during the last
75 years most of the outlets of SW, W, N and
NE Vatnajökull have once or more advanced
suddenly, although this period as a whole has
been a period of glacier recession. These ad-
vances are summarized in Table 1, and the
areas affected shown schematically on the map
fig. 12. The area of Dyngjujökull is more un-
certain tlian the others, as we do not know to
what degree the E part of that glacier has been
affected. We find that at least twice, in 1934
and 1963/64, sudclen advance of a glacier on
the north side has coincided with an advance
of a southern glacier. Wliether or not any of
the W and SW outlets also advanced suddenly
1890 we do not know. Altogether about 3200
km2, or nearly 40% of Vatnajökull’s area, have
been affected by sudden advances during the
last 75 years. All the Vatnajökull glaciers that
JÖKULL 1964
article) that the thrust moraines formed in
front of the advancing glaciers are on the whole
very small and on long stretches practically
'nonexisting.
N. Nielsen, who went to Vatnajökull again
via Sídujökull in 1936, when the glacier was
still very broken up, was of the opinion that
the sudden advance of this glacier in 1934 was
“a slow glacierburst, caused by a subglacial
eruption pouring out a subglacial lava flow”
(Nielsen 1937a, p. 19, 1937b).
Nusser explains the 1934-advance of Dyngju-
jökull in a similar way (Jonas, op. cit., p. 189).
Iri a paper, 1938, the present writer accepted
Nielsen’s view, but soon became sceptical
against volcanological or seismological explana-
tions of the sudden advances of the outlets of
Vatnajökull (cf. Thorarinsson 1943, pp. 36—37).
In the material collected in the present article
regarding the sudclen advances there is nothing
85