Jökull - 01.01.2010, Blaðsíða 193

The retreat of Breiðamerkurjökull at Skálabjörg, SE Iceland
covered by a thick layer of mud. Remnants of ice
floes (lake ice) were found lying on the lake floor,
testifying to a recent draining of the lake. A large
entrance of a subglacial channel is clearly visible at
the bottom of the basin. The channel drains the lake
frequently and rapidly, sometimes in a matter of sever-
al hours (Björnsson, 1976). This probably results
from dynamic changes in subglacial drainage caused
by fast flow of the temperate glacier with a steep mass
balance gradient (Björnsson et al., 2001; Evans and
Twigg, 2002), which favours quick changes in sub-
glacial drainage network.
Table 4. Rounding of stones on the LIA moraine ridge
and on an older surface (directly above the ridge). A
- angular, SR - subrounded, R - rounded, WR - well-
rounded (Reichelt, 1961). – Niðurstöður mælinga á
ávölun steina á jökulgarði frá Litlu ísöldinni.
rounding classes freq. %
LIAmoraine ridge
A 39
SR 40
R 21
WR 0
Older surface
A 70
SR 21
R 9
WR 0
PERIGLACIAL MODIFICATION OF
SKÁLABJÖRG
Small-scale solifluction tongues and lobes (Figures
2J, 6 and 8) and sorted small and large scale stripes
(Figures 2K, 2L, 6 and 9) occur on the top of sout-
hern Skálabjörg. The substratum is sandy-clayey re-
golith, and possibly remnants of old glacial till. It has
been several times translocated by solifluction (docu-
mented by layers enriched in gravel, see Figure 8) and
overlain by a black sandy layer (7–35 cm thick), in-
terpreted as volcanic ash. Due to a limited fraction of
silt in the black sandy layer (Figure 3), the uppermost
sediment is not frost susceptible according to Beskow
(1935), meaning that segregated ice, responsible for
significant frost heave, is not likely to develop in the
sediment. However, there may be some frost hea-
ve of the ground surface due to frost-susceptibility of
underlying weathered material. The total thickness of
unlithified deposits which may have undergone dist-
urbances like frost heaving, sorting and solifluction,
ranges from a few centimetres to over 2 meters.
1,8
m
1,0 m
0 cm
30
40
55
80
110
120
135
163
175
200
10
30
8
o
o
o
A
B
C
D
E
F
G
H
I
J
K
A - black sand (volcanic ash)
B - angular fragments of basalt in black-brown sand
C - brown sandy diamicton with sparce basalt fragments
D - brown sandy diamicton
E - angular fragments of basalt in brown sandy diamicton
F - brown sandy diamicton
G - angular fragments of basalt in brown sandy diamicton
H - brown sandy diamicton
I - gravel in black-brown sand
J - reddish sandy diamicton
K - lithified volcanic breccia
plan view cross-section
Figure 8. Small solifluction lobe in the southern part
of Skálabjörg. – Setsamsetning lítillar jarðskriðs-
tungu í sunnanverðum Skálabjörgum.
Solifluction tongues, lobes and sorted stripes occ-
ur on slopes inclined from 5◦ to 16◦. Average di-
mensions of solifluction tongues are 8 m of length and
4 m of width whereas solifluction lobes are typically
0.8 m long and 1.5 m wide (Figure 8). The majority
of the forms are not covered by vegetation and have
steep fronts (20◦–30◦) armoured with clasts lying at
high angles, testifying to present-day activity of the
tongues and lobes.
Small-scale sorted stripes have a coarse domain
comprised of gravel (Figure 2K). Their average length
is c. 2.5 m and spacing between the coarse stripes is
typically 20–30 cm. Sorting is shallow reaching less
then 10 cm. Large-scale sorted stripes have a coarse
domain dominated by pebbles and cobbles (Figures
JÖKULL No. 60 193