Jökull - 01.01.2020, Side 23

Hannesdóttir et al.
From the study of Brynjólfsson et al. (2015) it
is known that the surges of the outlet glaciers of
Drangajökull (Reykjafjarðarjökull, Leirufjarðarjök-
ull and Kaldalónsjökull, see Figure 8) were non-
synchronous. Therefore, the ice margin reached its
farthermost position at different times at different lo-
cations. Each of these glaciers has surged several
times since 1700 and they then extended 3–4 km far-
ther down-valley than at present.
Þórarinsson’s (1943) analysis was carried out be-
fore understanding of the effect of surges on glacier
variations. Some of the conclusions of his analysis
may reflect the effect of a surge on individual out-
let glaciers rather then a general expansion of the en-
tire ice margin. It is possible that further examination
of historical information about travel routes over and
near the ice cap in recent centuries will provide more
clues to delineate the maximum LIA extent of the ice
cap with more certainty.
The glacier reconstructions of the LIA extent by
Brynjólfsson et al. (2014) and Harning et al. (2016)
(Figure 8), differ mainly in the southeastern part of
the ice cap (in the highland area called Hraun), re-
sulting in a LIA maximum area difference of 50 km2
(220 km2 reported in Brynjólfsson et al., 2014, and
270 km2 published by Harning et al., 2016). Our LIA
maximum outline of Drangajökull is based on the re-
construction of Harning et al. (2016), which is sup-
ported by data from lake sediments and detailed field
observations.
Measurements by the Danish General Staff
in 1912 (Danish Geodetic Institute, 1941a) show
Drangajökull with an area of 200 km2 and a smaller
extent of the southeastern part of the ice cap, com-
pared with the maximum LIA extent of both Bryn-
jólfsson et al. (2014) and Harning et al. (2016) (see
Figure 8). The geological map by Þorvaldur Thor-
oddsen (1901), based on his own field observations
in 1886 (Thoroddsen, 1887), indicates an even larger
ice cap near the end of the 19th century with an area
of ca. 350 km2, and Björn Gunnlaugsson’s map from
1844 shows a much larger ice cap still, with an area
>550 km2 extending all the way to the Steingríms-
fjarðarheiði mountain overpass (see Figure 1) towards
southeast (Þórarinsson, 1943, 1974). It should be
born in mind that neither Gunnlaugsson nor Thorodd-
sen visited the area in question on the south side of
Drangajökull.
A highland area at 700–800 m a.s.l. on the north-
west of Drangajökull, north of Kaldalón (Figure 8),
is included within the LIA maximum extent of the
ice cap and contributes with ∼10–15 km2 to the LIA
maximum area of Drangajökjull in Tables 2 and 3. It
is uncertain whether this part of the ice cap was ever
dynamically connected to the main Drangajökull ice
cap. The same may apply to parts of the larger area
on the highland on the southeast side of the ice cap (in
Hraun), discussed in the previous paragraph. These
areas may have been partly or largely covered with
perennial snow and firn rather than glacier ice. This
may be the explanation that there is proportionally a
larger change in area for Drangajökull between LIA
maximum and 1945 than for any other of the main ice
caps. The above mentioned earlier LIA maximum of
Drangajökull, around the middle of the 19th century,
compared with ∼1890 for the other main ice caps,
may also partly explain this proportionally larger area
change which, thus, took place over a longer time in-
terval for Drangajökull.
The so-called Glámujökull “ice cap” south of Ísa-
fjarðardjúp in Vestfirðir (see Gláma highland in Fig-
ure 1) is not included in our list of glaciers during the
LIA in Iceland, as it was observed to be merely dis-
connected snow patches in 1893 and is, therefore, un-
likely to have been a substantial ice body during the
LIA (Sigurðsson, 2004). The Glámujökull “ice cap”
is, however, mapped as a glacier on several maps of
Iceland dating from the 18th and 19th centuries and
described as a glacier in many historical documents.
Snæfellsjökull (located near the western end of the
Snæfellsnes peninsula) has lost 16 km2, and currently
has only 35% of its maximum LIA extent. The main
area loss occurred on the northern side, where the out-
let glaciers have retreated 1.5–2 km; this is where the
glacier reached the lowest elevation (Figure 9).
The maximum LIA extent of Snæfellsjökull has
been delineated from detailed mapping (Evans et al.,
2016a). The average thickness of Snæfellsjökull in
2003 was only 30 m according to radio-echo sound-
ings (Davíðsdóttir, 2003). Between 1999 and 2008,
20 JÖKULL No. 70, 2020