Jökull - 01.01.2012, Síða 6

S. Steinþórsson
The Icelandic glaciers, having reached their great-
est extent for 10.000 years in the late 19th century,
were by this time shrinking ever more rapidly. The
International Commission of Glaciers had urged the
monitoring of advance and retreat of glaciers, but the
aim of the expedition went a step further: to elucidate
the glaciological and climatic causes of the observed
phenomena. It was also hoped that the research might
cast light upon the cause of ice ages and the behavior
of the Pleistocene glaciers.
The best way, and in fact the only reliable one
for assessing the mass balance of a glacier, is to dig
or drill down through the annual snow layer to mea-
sure its thickness. The summer of 1936 was singu-
larly well suited for this purpose since the ash from
the Grímsvötn eruption in 1934 formed a clear time
marker. From the beginning of May to mid-June the
party of six dug twelve deep trenches, up to 7 meters,
through the winter layer from 1935–1936, and then
drilled with a corer down to the 1934-ash layer. Var-
ious measurements and observations were made on
the snow in the trench-walls in addition to its thick-
ness, including temperature and density. Furthermore,
daily weather observations were conducted, innumer-
able shallower trenches dug and bamboo poles driven
into the snow to monitor the day-to-day ablation. In
mid-June Ahlmann and Jón Eyþórsson left together
with two assistants, leaving Sigurður and fellow stu-
dent Mannerfelt alone to tend the trenches and poles
for two additional months.
Sigurður Þórarinsson continued the work on
Vatnajökull the following two summers, 1937 and
1938. Together, he and Ahlmann published a series
of nine articles in Geografiska Annaler from 1937
to 1940 based on the Vatnajökull work. These in-
cluded Sigurður’s fil.-kand. thesis about the glacier
Hoffellsjökull (1937) and his fil.-lic. thesis about
glacier-dammed lakes in Iceland (1938). In 1943 the
Vatnajökull series appeared as a 306-page book en-
titled Vatnajökull. Scientific Results of the Swedish-
Icelandic Investigations 1936-37-38. In addition, Sig-
urður published a much-quoted overview article in
1940 estimating the volumes and rates of shrinking of
the World’s glaciers and how that affects the volume
of the sea.
After this intensive work on Vatnajökull, almost a
decade passed before Sigurður put foot on the glacier
again, in August 1946, that time as member of the first
motor-sledge expedition on Vatnajökull. One purpose
was to map the watershed area of Grímsvötn and mea-
sure its snow-accumulation, and the previous winter
Sigurður had worked through available records about
earlier eruptions in Vatnajökull and associated jökul-
hlaups. That work was later (1974) to bring fruit in a
book on Grímsvötn and the associated jökulhlaups.
In 1952 Sigurður read a paper on Grímsvötn to the
British Glaciological Society in Cambridge, in which
he introduced a new model for the manifest relation-
ship between Grímsvötn eruptions and jökulhlaups.
At that time N. Nielsen’s theory was generally ac-
cepted: that melting by the eruption caused the flood,
but Sigurður showed it to be the other way round:
pressure release in the caldera due to the flood triggers
the eruption. The idea, initially based on his work on
floods from ice-dammed lakes, was supported by nu-
merical observations and is now generally held true
for eruptions within the Grímsvötn caldera that ac-
company jökulhlaups.
All in all, Sigurður was author of some 50 articles
on glaciology in addition to the book on Grímsvötn
(1974) and a great number of reports. He was pres-
ident of the Iceland Glaciological Society from 1969
till his death, leader of most of its annual expeditions
to Vatnajökull from 1953 onwards, and a frequent co-
editor and contributor to its journal Jökull.
Þjórsárdalur 1939
In the summer of 1939 Sigurður joined a group of
Nordic archaeologists excavating ruined medieval
farmsteads in the valley Þjórsárdalur. The ruins were
buried beneath a layer of white volcanic ash and Sig-
urður’s purpose was to date the ash and by inference
the end of habitation in the valley. The farm Stöng
was excavated by Aage Roussell and Kristján Eld-
járn, and the farm and cemetery of Skeljastaðir by
Matthías Þórðarson, director of the Iceland National
Museum. Sixty-six skeletons were unearthed from
the cemetery and studied anthropologically by Jón
Steffensen, professor of medicine.
4 JÖKULL No. 62, 2012