Jökull - 01.01.2019, Blaðsíða 107

Tussetschläger et al.
rock glaciers in Tröllaskagi can be differentiated in
moraine- and talus-derived landforms, and their ac-
tivity includes both intact and relict rock glaciers
(Lilleøren et al., 2013; Tanarro et al., 2019). The
MAAT in coastal areas of northern Iceland at sea level
was 2 to 3◦C between 1971 and 2000 (Tveito et al.,
2000). On the Tröllaskagi peninsula the estimated
MAAT ranges between 2 to 4◦C at the coast, and -4
to -2◦C at the summits for the period from 1940 until
1970 (Einarsson, 1984). The estimated mean precip-
itation increases from 1000–1500 mm in the coastal
areas up to 2000–2500 mm at higher elevations. How-
ever, precipitation in some inland valleys of the penin-
sula is less than half the precipitation in areas close to
the sea (Crochet et al., 2007; Brynjólfsson and Ólafs-
son, 2009).
Frequent cloud cover on available satellite images
over the Tröllaskagi peninsula made it necessary to fo-
cus on six sub-regions (Figure 1). Region 1 is called
Almenningar, a mountain slope of variable steepness
extending from the open sea up to 750 m a.s.l. on the
west side of the northernmost part of the Tröllaskagi
peninsula. A big landslide extends from the upper-
most part of the mountain slope down to the ocean.
Slow downward movements or faltering of parts of
the landform occur in anomalously wet periods, dur-
ing which the stability and the substrate conditions of
the landform seem to be affected (Sæmundsson et al.,
2004), However, Guðmundsson (2000) described the
same landform as an active rock glacier and suggested
that the movement relates to its internal ice conditions.
Region 2, Úlfsdalir, opposite to the first region Al-
menningar, is located on the east side of the moun-
tain ridge between the areas in a north facing valley
bottom about 400–900 m a.s.l. Small debris flows and
rockfall apparently affect the steepest and uppermost
part of the valley bottom which otherwise is charac-
terised by gentle topography and morphology. Re-
gion 3, the valley Brimnesdalur, is a north facing val-
ley surrounded by peaks reaching about 1100 m a.s.l.
At the head of the valley is the Brimnesjökull glacier
with an area of about 0.63 km2, almost half of which
is debris covered. Several distinct landforms were
observed during fieldwork, especially in the moun-
tains on the east side of the valley, both relative old
morainic features and debris piles or moraines that
seem fresh and ice cored even though they do not cor-
relate with the present glacier. Region 4 is the Kerl-
ing area, a small northeast facing cirque located on
the east side of the mountain Kerling about 35 km in-
land from the first three regions. The high and steep
back walls of the cirque reach up to 1200 m a.s.l. and
are the main source for a small talus-derived, tongue-
shaped rock glacier situated on the cirque bottom be-
tween 800–1000 m a.s.l. Region 5 is the Búrfellsdalur
valley, a north facing valley, tributary of the main val-
ley Svarfaðardalur, located about two kilometres west
of the Kerling area. Búrfellsjökull glacier is located at
the head of the valley between 750–1220 m a.s.l., the
surrounding mountains reach 1200–1300 m a.s.l. The
size of the mostly debris free-glacier is currently about
1.3 km2. A prominent debris lobe feature originat-
ing below a steep talus-characterised mountain slope
proximal to the glacier margin on the west side of the
valley was mapped by Brynjólfsson et al. (2012). The
landform extends from about 900 down to 700 m a.s.l.
and at least the upper half contains ice. Fresh cracks
and surface morphology indicate a slow downward
movement of the landform. Region 6 is the Sakka
area, extending from 160–920 m a.s.l., on the west
side of the mountain above the farm Sakka. A promi-
nent landslide is located in the northernmost part of
this area. Observations of the surface morphology in
the uppermost part of the landslide, e.g. fresh cracks,
hollows and ridges indicate considerable movement
of at least the upper part of the landslide.
MATERIALS AND METHODS
Dataset
Optical satellite images from Sentinel-2 and Landsat-
5/-7/-8, aerial images (acquired by Landmælingar Ís-
lands), orthophotos (acquired by Loftmyndir) and a
digital elevation model were used as input for the
classification of perennial snow patches. Suitable
Sentinel-2 and Landsat-5/-7/-8 images for the Trölla-
skagi Peninsula were ranked based on suitable illu-
mination conditions and cloud cover. For the classi-
fication we used only images acquired at the end of
summer, when most of the snow from previous winter
106 JÖKULL No. 69, 2019