Jökull - 01.01.2019, Side 23

Guðmundsson et al.
ber, Stemmulón had become three smaller lakes with
a combined area of ∼2.5 km2. The following year,
Stemmulón had become part of Jökulsárlón, which
consequently grew from 9.5 to 11.5 km2.
Jökulsárlón has grown rapidly since the mid-
1990s, and its size more than doubled in 1991–2018.
In 2018, the lake was over 8 km long, 27 km2 in area
and 260 to 300 m deep (according to measurements
in 2017) and had become the deepest lake in Iceland
(Figure 18). The average rate of growth in 1933–1991
was ∼0.2 km2 a−1 but ∼0.6 km2 a−1 in 1991–2018.
The glacier-bed topography of Breiðamerkurjök-
ull revealed by radio-echo sounding measurements in
the 1990s (Björnsson and others, 1992; Björnsson,
1996, 2009a) shows that the calving terminus in Jök-
ulsárlón is currently located at the deepest part of a
25 km long valley below sea level (Figure 15) where
a ∼80 km2 tidal lagoon will eventually form if the
glacier retreats out of the subglacial depression. The
current volume of the lake is ∼2700×106 m3 accord-
ing to these measurements.
Veðurárlón
The river Veðurá changed course around 1930 and
started to flow into Stemmulón which was forming by
Brennhólaalda (Figures 15 and 16). This development
increased the discharge of the river Stemma substan-
tially (Imsland, 1990). The lake Veðurárlón started to
form later in the 1930s and grew rapidly at first. It
had grown to > 0.1 km2 in 1945. The lake continued
to grow as the glacier terminus retreated with outflow
towards the west into Stemmulón, usually along the
glacier margin. Outflow along the present rivercourse
towards the south and then into Stemmulón from the
east started in the 1960s. Veðurárlón had an area of
0.8 km2 in 2018.
Ice-dammed lakes in Innri-Veðurárdalur, Jökuldalur
and Fossadalur
Several small ice-dammed lakes were formed in side
valleys and depressions by the margin of Breiðamerk-
urjökull during the 20th century. The maps of the
DGS (1905a) show two such lakes at the western
glacier margin in 1904, in Hrossadalur and Jökuldalur
in Breiðamerkurfjall, 0.003 and 0.5 km2 in area, re-
spectively. Jökulhlaups were often released from the
lake in Jökuldalur during the 20th century (Björnsson,
1962). The lake level decreased from 220 m a.s.l. in
1904 to 180 m a.s.l. in 1945 when the area had been
reduced to 0.3 km2 (Figure 15). There is no lake in
Jökuldalur at present.
The lake in Innri-Veðurárdalur most likely started
to form in the 1930s. It wasn’t present in 1932 but had
formed well before 1945 (Fjölnir Steinþórsson, pers.
comm. 2018), (Figure 15). Jökulhlaups into Veðurár-
lón that continue into Jökulsárlón may have been re-
leased from Innri-Veðurárdalur but it is also possible
that jökulhlaups from Veðurárdalur in the early 20th
century flowed directly to Jökulsárlón (F. Björnsson,
1993), and then emerged in Jökulsá. According to the
AMS (1951) map, the area of the lake was 1.3 km2
in 1945 and the lake level close to 450 m a.s.l. The
same map also shows a few other small lakes by the
eastern glacier margin in 1951. The lake in Innri-
Veðurárdalur was approximately 0.7 km2 in 2018 and
the lake level close to 320 m a.s.l.
A lake formed in Fossadalur in Esjufjöll before the
turn of the century (Figure 15). Photographs by Hjör-
leifur Guttormsson show that an incipient lake had ap-
peared in 1988. Its area was ∼0.3 km2 in 2000 and it
had grown to > 1 km2 in 2018. If the retreat and low-
ering of the glacier continues, these lakes will eventu-
ally disappear because the bottom of the side valleys
slopes towards the valley occupied by Breiðamerkur-
jökull. A small lake, < 5 ha in area, has sometimes
formed below Eyjólfsfell during the last decade. This
lake has been emptied periodically, with irregular in-
tervals.
Glaciers in the Suðursveit, Mýrar and Horna-
fjörður districts
The largest outlet glaciers in the Suðursveit, Mýrar
and Hornafjörður districts are Skálafellsjökull, Heina-
bergsjökull, Fláajökull and Hoffellsjökull. They flow
from the Breiðabunga ice dome to the lowland and
have all carved subglacial valleys that reach below sea
level according to radio-echo sounding measurements
(Björnsson, 2009a). They have all retreated > 2 km
from their LIA maximum extent (Hannesdóttir and
others, 2014, 2015a). The current terminus lakes are
formed in the outermost part of the subglacial valleys.
Lakes by the smaller Brókarjökull and Fellsárjökull
22 JÖKULL No. 69, 2019