Jökull - 01.01.2019, Page 2

Terminus lakes on the south side of Vatnajökull ice cap,
SE-Iceland
Snævarr Guðmundsson1∗, Helgi Björnsson2, Finnur Pálsson2,
Eyjólfur Magnússon2, Þorsteinn Sæmundsson2,3 and Tómas Jóhannesson4
1South East Iceland Nature Research Center, Nýheimar, Litlubrú 2, IS-780 Höfn í Hornafirði, Iceland
2Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland
3Department of Geography and Tourism, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland
4Icelandic Meteorological Office, Bústaðavegur 7–9, IS-108 Reykjavík, Iceland
∗Corresponding author: snaevarr@nattsa.is https://doi.org/10.33799/jokull2019.69.001
Abstract — Many ice-marginal lakes have formed in front of glacier termini in Iceland in recent decades due
to climate warming, particularly at the southern margin of Vatnajökull ice cap where several such lakes grow
year-by-year at present. At the same time, most glacier-dammed lakes at the lateral ice margins have shrunk
or disappeared because of glacier thinning, and jökulhlaups released from them have become smaller. This
paper describes changes in glacial lakes in SE-Iceland, from Skeiðarárjökull west of Öræfi to Hoffellsjökull in
Hornafjörður. Lakes started to form in front of several glaciers in this area in the 1930s but most did not grow
much until the 1990s, except for Jökulsárlón by Breiðamerkurjökull, which has grown steadily since before the
middle of the last century. Currently, there are growing terminus lakes by all the main south-flowing outlet
glaciers of Vatnajökull, with a combined area of ∼60 km2. The subglacial landscape upstream of the termini
indicates that the lakes will continue to grow in the coming decades as a consequence of glacier downwasting
if the climate warms as projected. These lakes affect the ice flow and the mass and energy balance of the
respective glaciers because of their effect on the force balance of the terminus region, the calving of ice into
the lakes, and the absorption of heat spent for melting of calved ice fragments and the terminus ice front. The
lakes can cause hazard to settlements and travellers in the adjacent area, as landslides on the glaciers that
propagate into the lakes can create tsunami waves with a high run-up and sudden, very dangerous flash floods
in the glacier forelands.
INTRODUCTION
Several ice-marginal lakes were formed in front of
glacier termini in SE-Iceland in the first half of
the 20th century (F. Björnsson, 1993; H. Björnsson,
1976a, 2009a). Glacier-dammed lakes at the lat-
eral ice margins, such as Grænalón by Skeiðarár-
jökull and Vatnsdalslón by Heinabergsjökull, releas-
ing regular jökulhlaups (glacier outburst floods), and
Vatnsdalslón by Brókarjökull, that had released jök-
ulhlaups more or less annually before 1870, were
well known at this time (Thorarinsson, 1939; Rist
and Þórarinsson, 1970; Rist 1973, 1981, 1984a;
H. Björnsson, 1976a, 2002, 2009a,b; Sigurðsson and
others, 1992; Jónsson, 2004). The retreat of the
glacier termini accelerated in the 1930s and 1940s,
producing ice-marginal lakes in depressions evacu-
ated by the glaciers. Most of the lakes grew slowly
at first and some stopped growing when the glaciers
were separated from the lakes as they retreated farther.
Lakes formed in deep troughs carved by the glaciers
continued to grow, however, in particular Jökulsárlón
by Breiðamerkurjökull.
JÖKULL No. 69, 2019 1