Jökull - 01.01.2019, Side 25

Guðmundsson et al.
19th century, jökulhlaups down to the Steinasandur
outwash plain were released from this lake more or
less every summer until 1870, or even longer, damag-
ing fields and vegetated areas. The glacier most likely
advanced beyond the Vatnsdalur valley around 1800.
The Kálfafellsdalur valley was well vegetated around
1815 but the erosion of farmland by Steinavötn river
had already started by that time. The farm Steinar, lo-
cated south of Kálfafellsdalur, was abandoned in 1829
because of damage caused by erosion of the farmland
by the river (Henderson, 1957; Guðmundsson, 1972;
Jónsson, 2004; Fjölnir Torfason, pers. comm. Novem-
ber 2018).
Brókarjökull has by now retreated > 2.5 km from
the LIA maximum extent, with a particularly rapid
rate of retreat during the last several decades. A ter-
minus lake was formed in dead ice in front of the re-
treating terminus sometime after 2005. The lake was
0.02 km2 in 2008 and 0.07 km2 in 2012. The lake has
shrunk slightly in recent years and the lake area was
down to 0.06 km2 in 2018. The glacier has now re-
treated out of the lake, which may disappear in the
future due to accumulation of sediments.
Skálafellsjökull and Heinabergsjökull
A map by H.H. Eiríksson (1932) indicates that a small
lake was located by Skálafellsjökull in 1930 (Figures
20 and 21). Lakes formed by Skálafellsjökull and
Heinabergsjökull in the late 1930s, near Hafrafell-
sháls in the area where the glaciers had separated in
the early 1930s (Guðmundsson, 1972; Gísli Arason
[1918–2017], pers. comm. July 2016). In 1945, the
lakes in front of Skálafellsjökull and Heinabergsjök-
ull were ∼0.04 and ∼0.12 km2 in area, respectively
(AMS, 1951). Neither of them was located in the area
where the current lakes later formed, and both disap-
peared with the continued retreat of the glaciers.
Around or before 1945, small lakes were formed
in dead ice near the path of Heinabergsvötn ap-
proximately 0.5 km east of Skálafellsjökull. The
Heinabergsvötn river from Heinabergsjökull glacier
changed course westwards through these lakes shortly
thereafter in 1948 and merged with Kolgríma river
from the Skálafellsjökull glacier, and these rivers have
flowed together in a common path since then. At this
time, Heinabergsvötn river flowed through a small ter-
minus lake by Heinabergsjökull with area ∼0.1 km2.
This predecessor of Heinabergslón lake later vanished
as the terminus retreated into the watershed with the
present lake. The current lake in front of Skálafells-
jökull started to form in the 1960s. It is small in com-
parison with Heinabergslón, with an area of 0.25 km2
in 2018, and its size has not changed much during the
last decade (Figure 21).
The current Heinabergslón lake started forming
around the middle of the 20th century and had grown
to 0.6–0.7 km2 by the end of the 1960s. At the
turn of the century it was > 1.5 km2, and in 2018
> 3 km2, with a volume of ∼210×106 m3 according
to the radio-echo sounding map of the bed (Björnsson,
2009a). The outermost 4 km of the terminus of Heina-
bergsjökull became afloat somewhat before 2010 and
the glacier terminus has broken up to a considerable
extent since then. The floating tongue is currently
in the process of disintegrating, so it is likely that
substantial changes will take place at the terminus of
Heinabergsjökull in the near future.
Further retreat of the termini of Skálafellsjökull
and Heinabergsjökull may lead to the formation of
> 200 m deep lakes in subglacial troughs. The lakes
will eventually become > 3 and 11 km long and > 2.5
and ∼11 km2 in area, respectively, if the glaciers re-
treat out of the subglacial depressions (Björnsson,
2009a).
Vatnsdalslón and Dalvatn
Heinabergsjökull dams lake Vatnsdalslón in the side
valley Vatnsdalur to the northeast of the glacier, west
of Geitakinn mountain (Figure 20). The glacier was
sufficiently thick during the 19th century that the
runoff from the lake was into the river Dalá along
Heinabergsdalur valley (Thorarinsson, 1939; Björns-
son, 1976a). Heinabergsdalur was then dammed by
Heinabergsjökull, which extended across the mouth
of the valley at the end of the 19th century, and
another lake, Dalvatn, was formed upstream of the
glacier terminus. The glacier had started to retreat
and thin after 1887, and outflow from Vatnsdalur into
Heinabergsdalur ceased when the glacier became too
thin to maintain sufficient water level for the water to
24 JÖKULL No. 69, 2019