Jökull - 01.12.1972, Síða 32

forming its inner walls provides a constricted
outlet for the Kverkfjöll outlet glacier on the
northern end of the massif.
Hveradalur, the solfatara valley of Kverkfjöll
vestri, trends north-northeast on the northwest
flank of the Kverkfjöll massif, following a
structural trend parallel to other volcano-tec-
tonic lines of western Vatnajökull ancl the
southern part of the neovolcanic zone. The
high-elevation geothermal area of Kverkfjöll
eystri is associated with the precipitous escarp-
ment north and south of Skarphédinsjökull
(Fig. 2) and is presumably also linear, with
north-northeast surface trends roughly parallel
to tliose of Hveradalur in Iíverkfjöll vestri.
F. W. Anderson, who visited Kverkfjöll eystri
in 1932, described postglacial pillow lava at
the base of the above-mentioned escarpment
near Skarphédinsjökull (Atiderson 1949, p. 784
and Fig. 4). Evidence of volcanic activity in
Kverkfjöll and adjacent parts of Dyngjujökull
has been reported by Thoroddsen (1924, 1925),
Jónsson (1945), and Thorarinsson (1950).
Tephrafall in North Iceland in 1477 was prob-
ably caused by an eruption in Kverkfjöll or
its vicinity. Jökulhlaups (glacier outburst
floods), causing damage on the Jökulsá á Fjöll-
um delta on the north coast of Iceland, occurr-
ed in the years 1655, 1684, 1711/12, 1716?,
1717, 1726 and 1729 (Thorarinsson 1950). It may
be regarded as nearly certain that these floods
were volcanogenic as four of the jökulhlaups
(1684, 1716?, 1717, ancl 1726) coincide with
known volcanic eruptions in Vatnajökull, ancl
four (1655, 1684, 1711/12, and 1717) are too
big to have been caused by ice barricades in
the Jökulsá river or by the drainage of mar-
ginal ice-dammed lakes (Thorarinsson 1950). In
his 1950 paper Tliorarinsson concluded that
the most probable location of the eruption
center was beneath Dyngjujökull just north of
Kverkfjallahryggur, on the extension of the
Geirvörtur-Thórdarhyrna-Grímsvötn volcano-
tectonic line (Fig. lb), rather than in Kverk-
fjöll. His later repeated visits to Kverkfjöll
(the sixth and last one in 1968) have, however,
convinced him that large floods could also
have been caused by volcanic activity beneath
the accumulation area of Kverkjökull (south
of d on Fig. 4).
Thorarinsson described (1950 ancl 1953) and
30 JÖKULL 22. ÁR
sketchecl (1953) one major ancl several minor
ice cauldrons of Kverkfjöll vestri and attribut-
ed these to subglacial melting by solfatara
activity. He also noted (1953, p. 21) that Hvera-
dalur southwest of the biggest solfataras “seems
to be formed as a volcanic fissure”. Later he
noted (1962, p. 33) that a very young fissure
runs parallel with Hveradalur along its north-
west side. A small eruption may have occurred
in this area as late as about 1935. This is in-
dicated by a tephra layer observed in 1946 in
the firn walls of the Hveradalur Iake (Jökul-
lón); the tephra layer was in 1946 covered by
at least ten annual firn layers (Thorarinsson
1950, p. 129, cf. also Ó. Jónsson 1945, p. 318-
319).
After the Vatnajökull expedition of 1953,
Thorarinsson (1953, p. 19—22) provided the
most detailed description yet available of the
location and nature of the geothermal area of
Hveradalur (1953, Figs. 11—13) and Kverkfjöll
eystri. He also summarized the results of pre-
vious visits to Kverkfjöll, including earlier ob-
servations by P. Hannesson and S. Sigurclsson
in 1933 and Ó. Jónsson in 1941 and 1946
(Jónsson 1953). The many visits to Hveradalur
since 1953 by members of the Iceland Glacio-
logical Society have revealed that the change-
ability of the solfatara area is considerable.
New steam vents and solfataras are formed
while others diminish or disappear.
Fig. 3. Aerial photograph of Kverkfjöll vestri
and part of Kverkjökull outlet tongue. a) Linear
array of Hveradalur thermal features (perfora-
tions in glacier shown by arrows); b) Kverk-
jökull outlet tongue; c) thermal melt water
emerging from glacier portal; d) bedrock escarp-
ment separating Kverkfjöll vestri from Kverk-
jökull outlet tongue; g) Holocene volcanic
rocks; li) ablation zone of Dyngjujökull. Aerial
photograph by U. S. Air Force, 24 August 1960.
From Friedman et al., 1969, Fig. 10.
Mynd 3. Loftmynd af Kverkfjöllum vestri og
hluta af Kverkjökli, tekin 24. ágúst 1960. a)
Jarðhitalínan í Hveradal (örvar benda á göt
í jöklinum); b) sporður Kverkjökuls; c) frá-
rennsli undan jöklinum; d) hamrar, sem vita
að Kverkjökli; g) berg frá siðasta jökulskeiði
og yngra; h) leysingarsvœði Dyngjujökuls.