Jökull - 01.01.2020, Blaðsíða 17

Hannesdóttir et al.
(Sigurðsson, 2005). Tungnaárjökull reached its LIA
maximum around 1890 (Thoroddsen, 1933; Tómas-
son and Vilmundardóttir, 1967; Magnússon et al.,
2005), and its forefield has been mapped in detail
(Evans et al., 2009; Molewski et al., 2016). Skaft-
árjökull was slowly retreating from its outermost
moraines when Thoroddsen visited the area in 1893
(Thoroddsen, 1893, 1906), and so was Síðujökull
(Sigurðsson, 2005). These glaciers are both prone
to surges and so is Dyngjujökull, which was receding
when Thoroddsen inspected that part of the Icelandic
highlands in 1884 (Thoroddsen, 1906). The maximum
LIA glacier extent of the northwestern (Köldukvíslar-
jökull–Dyngjujökull) and eastern parts of the margin
(east of Eyjabakkajökull) of Vatnajökull ice cap have
not been studied in detail, and the LIA outline relies
solely on the geomorphological imprint detectable on
aerial photos and satellite images. The LIA extent of
Brúarjökull and Eyjabakkajökull has been mapped in
detail by Benediktsson et al. (2008) and Schomacker
et al. (2014), respectively.
The debris-covered snouts of Dyngjujökull,
Rjúpnabrekkujökull and the smaller outlets west of
Bárðarbunga were presumably connected to the ice-
cored LIA moraines during most of the 20th century.
In the last 10–20 years, the glacier terminus has been
retreating from the ice-cored moraine field, which
marks its maximum LIA extent according to our in-
terpretation. Further work on the glacier outlines in
this area is in progress. A DEM and orthoimage will
be created based on aerial images of 1945/1946 and
from the 1960s. This will enable a more thorough
evaluation of the terminus variations since the maxi-
mum LIA by DEM differencing which makes it pos-
sible to detect the active glacier margin.
Tungnafellsjökull, a small ice cap to the northwest
of Vatnajökull, decreased by 17 km2 during the pe-
riod ∼1890–2019, equal to 34% decrease relative to
its maximum LIA extent. The LIA extent of Tungna-
fellsjökull has been traced by identifying moraines
and other geomorphological evidence on satellite and
aerial images (Gunnlaugsson, 2016). Historical data
are sparse; however, Hans Reck visited Tungnafells-
jökull in 1907 and noted that the outlet glaciers were
receding at that time (Þórarinsson, 1943).
Hofsjökull, Langjökull and smaller neighbouring
glaciers
Hofsjökull ice cap decreased by 228 km2 during the
period ∼1890–2019, and similar to Vatnajökull, close
to half of the area loss occurred in the period ∼1890–
1945. The rate of area change is highest during
the first 2 decades of the 21st century, in the range
−3 km2 a−1 to −4.5 km2 a−1 (Table 3). The larger out-
let glaciers of Hofsjökull have retreated by approxi-
mately 2–3 km from the maximum LIA extent and the
retreat is fairly uniform around the glacier (Figure 5).
The maximum LIA extent of Hofsjökull has been
drawn based on geomorphological evidence detected
on aerial photos and satellite images. Hermann
Stoll (1911) travelled in the area in 1910 and men-
tioned that the outlet glaciers of Hofsjökull were re-
ceding from their outermost moraines at that time.
Sigbjarnarson (1981) reviewed available information
about the retreat of the northwestern part of the ice
margin (Sátujökull) from the LIA maximum to 1981.
He concludes that the outermost moraines must have
been built up during surges.
Langjökull ice cap has during the period ∼1890–
2019 lost 257 km2. The rate of area change since 2000
is in the range of −3.5 km2 a−1 to −5.3 km2 a−1 (Ta-
ble 3). The outlet glaciers that have experienced the
greatest area loss are on the eastern and southern side
of the ice cap, with their termini retreating 3–4.5 km
from the maximum LIA extent (Figure 6). The eastern
Hagafellsjökull glacier surged in 1974, 1980, 1999
(Björnsson et al., 2003), and the terminus advanced
by approximately 1 km each time. Leaving its termi-
nus in a more advanced position in 2000 than in 1973
for example (Figure 6).
The LIA extent of Langjökull has been delineated
from geomorphological field evidence, with support
from historical documents, maps and photographs
from the 19th century to the early 20th century, along
with field observations (e.g. Geirsdóttir et al., 2008).
Detailed oblique and aerial photographs support the
estimated maximum LIA extent (see Pálsson et al.,
2012, for further description).
The smaller glaciers in the vicinity of Langjök-
ull, namely, Þórisjökull, Eiríksjökull and Hrútfells-
jökull have lost 20 km2, 17 km2 and 6 km2, respec-
14 JÖKULL No. 70, 2020