Jökull - 01.01.2010, Blaðsíða 186

M. Da̧bski and P. Angiel
STUDY AREA
The Skálabjörg ridge, the largest of the Esjufjöll nuna-
taks, lies between approximately 550 and 1522 m
a.s.l. Steep slopes make it hard to access weathered
peaks in the northern and central parts of the ridge
(Figure 2A). The research was thus concentrated in
its southern part, where the surface is relatively flat
(Figure 2B) and logistics are facilitated by a hut, built
by the Icelandic Glaciological Society, at an altitude
of 710 m a.s.l.
The Esjufjöll nunataks are summits of the Esju-
fjöll central volcano within the Öræfi Volcanic Flank
Zone, just east of the Eastern Volcanic Zone. The
nunataks constitute the southeastern flank of a lar-
ge caldera (Holm et al., 2003). Historical activity
of the volcano has not been confirmed (Thordarson
and Larsen, 2007), but is considered possible (Björns-
son, 1977; Björnsson and Einarsson, 1990; Holm
et al., 2003; Guðmundsson and Högnadóttir, 2007).
The region is seismically active (Þorbjarnardóttir and
Guðmundsson, 2003). Volcanic rocks in Esjufjöll
are mostly ferrous-basaltic breccias, sometimes olive-
coloured tuffs cut in places by basaltic dikes which
are more resistant to weathering. According to the
Geological Map of Iceland (Jóhannesson and Sæ-
mundsson, 1998) the rocks are basic and intermediate
hyaloclastites formed in the Upper Pleistocene, youn-
ger than 0,8 Myr. A regolith on the top surface of
the southern part of Skálabjörg is made of sandy-silty-
clay and susceptible to frost heaving (Beskow, 1935).
In all sampled places, the regolith was covered by a
layer of non frost-susceptible black sand (Figure 3), 7
to 35 cm thick, which is interpreted as volcanic ash.
The maritime climate of S-Iceland has a lim-
ited number of days below freezing and therefore no
permafrost (Etzelmüller et al., 2007). Mean annual air
temperature in SE-Iceland ranges from 0 to -1◦C with
a mean annual temperature amplitude of 12◦. (Veð-
urstofa Íslands, http://andvari.vedur.is/vedurfar/ved-
urfarsmyndir/EV_DTO/ann.html; Szumska, 1998).
Precipitation in this region is high, c. 4000 mm,
because of windward exposure of the southern parts
of Vatnajökull. Such characteristics facilitate frequent
freeze-thaw cycles which are responsible for shallow
and frequent frost shattering and frost heaving of the
ground. Strong NW katabatic winds, frequent in this
area (Obleitner, 2000), are responsible for significant
intensity of wind deflation.
10 km
150
0
1000
50
0
Ö
B
F
V
S
E
A
16.5 Wo
64 No
Vatnajökull
Iceland
glacier margin
contours on the glacier
ice divide
ice-dammed lake
area shown on Fig. 4.
Atlantic Ocean coast
direction of ice flow
F
V
S
Fjallsjökull
Ö Öræfajökull
E Esjubjörg
A Austurbjörg
Vesturbjörg
Skálabjörg
B Breiðamerkurjökull
Figure 1. Location of the study area, modified from
Evans and Twigg (2002). – Kort af rannsóknasvæð-
inu í Esjufjöllum. Sjá einnig ljósmynd á bls. 197.
186 JÖKULL No. 60