Jökull - 01.01.2019, Síða 6

Terminus lakes on the south side of Vatnajökull
period 2000–2018. The largest lake is Jökulsárlón
at Breiðamerkursandur, with an area of ∼27 km2 in
2018, which first formed in 1933 (Figure 1). Breið-
árlón is a separate lake by Breiðamerkurjökull farther
to the west (∼6 km2) with outflow to Fjallsárlón lake
(∼4 km2). All glacial meltwater from Skeiðarárjökull
now flows to the river Gígjukvísl near the middle of
the Skeiðarársandur plain through several connected
terminus lakes with a combined area of ∼7 km2.
Glacier lakes in the Mýrar district east of Breiðamerk-
ursandur include Heinabergslón (> 3 km2) and lakes
by Fláajökull (∼2 km2) and Hoffellsjökull (∼5 km2).
Other smaller lakes in the Öræfi district with areas
∼1 km2 or less are by the termini of Morsárjökull,
Skaftafellsjökull, Svínafellsjökull, Virkisjökull, Kví-
árjökull and Hrútárjökull, and a small lake has formed
in front of Skálafellsjökull glacier in the Mýrar dis-
trict. Table 1 summarizes information about the area,
volume, the time of formation and some characteris-
tics of these lakes, the development of which is fur-
ther described in separate subsections below. Figure 2
shows the total area of the terminus lakes as a function
of time since the beginning of the 20th century and
figures in the corresponding subsections show varia-
tions in the area of the individual lakes.
Skeiðarárjökull
The maps of the Öræfi district by the DGS show that
Skeiðarárjökull had started to retreat from its LIA
maximum extent in 1904. The maps depict a lake
north of Háalda on the Skeiðarársandur plain, with an
area of ∼0.05 km2. The continued retreat of Skeið-
arárjökull by 0.3–1.2 km from 1904 to 1945 (AMS,
1951) led to the formation of lakes by the ice mar-
gin between Háalda and Sandgígjur. Most likely they
formed after 1938, since there was no depression in
front of the glacier and many small glacial rivers
emerged at scattered locations along the terminus be-
fore this time (S. Björnsson, 1998). The glacier then
retreated rapidly in the 1940s. Most of these lakes did
not last long as they were separated from the ice or
became part of the meandering branches of the glacial
rivers. Further lakes were created by the retreating ice
margin after 1945 (Eyþórsson, 1952, 1964) as shown
by the fieldwork of the Polish Geographical Expedi-
tion on Skeiðarársandur in 1968 (Galon, 1968) and
Landsat 1 images from 1973.
The current terminus lakes by Skeiðarárjökull
started to form around the turn of the century
(Gunnlaugsson, 2010). The Skeiðará river was di-
verted from its traditional path on the east side of
Skeiðarársandur to the river Gígjukvísl near the mid-
dle of the sandur plain in July 2009 (Magnússon and
others, 2009). The growing lakes by the east side
of the terminus are situated in an area of deepening
glacier bed geometry, and so is the lake farthest to the
west (Figure 3). These lakes will continue to grow as
long as the ice margin retreats since the glacier bed
slopes down away from the current ice margin to be-
low sea level. Changes in the extent of these lakes are
mapped in Figure 4 and the variation in their area in
Figure 5. The combined area of the lakes was ∼7 km2
in 2018 and has on average grown by ∼0.4 km2 a−1
since 2000. Based on the radio-echo sounding map of
the glacier bed (Björnsson and others, 1999a; Björns-
son, 2009a) and the water level in the lakes in 2017–
1900 1920 1940 1960 1980 2000 2020
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Figure 2. Variations in the total area of terminus lakes
(excluding ice-dammed lakes) from Skeiðarárjökull to
Hoffellsjökull, 1904–2018. Dates of maps and remote-
sensing imagery as well as on-site observations of lake
formation are denoted by circles. Limited information
is available from 1904 to the 1930s. – Breytingar á
heildarflatarmáli sporðlóna við sunnanverðan Vatna-
jökul, 1904–2018. Hringir sýna tímasetningu korta,
loftmynda og gervihnattamynda sem og upplýsingar um
myndun lóna. Litlar upplýsingar eru frá 1904 og fram
á fjórða áratuginn.
JÖKULL No. 69, 2019 5