Acta geographica Slovenica, 60-2, 2020, 175–190
CHANGES IN THE SKUTA GLACIER
(SOUTHEASTERN ALPS) ASSESSED
USING NON-METRIC IMAGES
Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn
Crevasse on the Skuta Glacier in 1913 (Kunaver 1913).
J o S IP k U N A v E R

Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn, Changes in the Skuta Glacier (southeastern Alps) assessed …
DOI: https://doi.org/10.3986/AGS.7674
UDC: 91:551.324(234.323Skuta)
528.7:551.324(234.323Skuta)
COBISS: 1.01
Mihaela Triglav Čekada
1
, Patricija Barbo
2
, Miha Pavšek
3
, Matija Zorn
3
Changes in the Skuta Glacier (southeastern Alps) assessed using non-metric images
ABSTRACT: The Skuta Glacier in the Kamnik–Savinja Alps (in northern Slovenia) is one of the two remain-
ing glaciers in Slovenia. It is located in a cirque oriented toward the northwest, which shields it from sunlight
for most of the year. The glacier lies at an average elevation of 2070 m. In recent years, its average area has
measured around 1.5 hectares. Monitoring of the glacier has been performed since 1946. In 1962, regular
photographing of the glacier with various cameras started from various non-fixed standpoints. Using the sin-
gle image interactive orientation acquisition method, in which a single photograph is compared with the
projection of a modern digital terrain model, seventeen photographs covering the period from 1970 to 2015
were used to acquire the 3D-perimeters of the glacier. The data shows that the elevation of glacier’s upper
edge decreased by approximately 40m in the last half-century. Changes in the glacier’s area and average upper
edge elevation were compared with average annual temperature and maximum seasonal snow cover depth.
KEY WORDS: very small glacier, glacieret, climate change, non-metric images, interactive orientation, Skuta
Glacier, Slovenia
Ugotavljanje sprememb na Ledeniku pod Skuto (jugovzhodne Alpe) na podlagi
nemerskih fotografij
POVZETEK: Ledenik pod Skuto v Kamniško-Savinjskih Alpah je poleg Triglavskega ledenika eden od dveh
še ohranjenih preostankov ledenikov v Sloveniji. Leži v krnici z usmerjenostjo proti severozahodu, zato
je večino leta v senci. Ledenik ima povprečno nadmorsko višino 2070 m, njegova površina pa je bila v zad-
njih nekaj letih okrog poldrugega hektarja. Ledenik merijo od leta 1946, od leta 1962 pa so ga z različnimi
fotoaparati tudi redno fotografirali iz različnih nestabiliziranih stojišč. S pomočjo interaktivne metode ori-
entacije, pri kateri vsebino na fotografijah primerjamo s projekcijo sodobnega digitalnega modela reliefa,
smo preučili 17 posnetkov in iz njih izmerili trirazsežnostne obode ledenika v obdobju 1970–2015. V zad-
njega pol stoletja se je ledenik na zgornjem robu stanjšal za skoraj 40 m. Spremembe površine in povprečne
višine zgornjega robu ledenika smo primerjali s povprečno letno temperaturo in največjo sezonsko skupno
višino snežne odeje.
KLJUČNE BESEDE: majhni ledeniki, podnebne spremembe, nemerske fotografije, interaktivna orientacija,
Ledenik pod Skuto, Slovenija
The paper was submitted for publication on 6th November, 2019.
Uredništvo je prejelo prispevek 6. novembra 2019.
176
1
Geodetic Institute of Slovenia and Faculty of Civil and Geodetic Engineering, University of Ljubljana,
Ljubljana, Slovenia
mihaela.triglav@gis.si (https://orcid.org/0000-0002-4200-2616)
2
barbo.patricija@gmail.com
3
Research Centre of the Slovenian Academy of Sciences and Arts, Anton Melik Geographical Institute,
Ljubljana, Slovenia
miha.pavsek@zrc-sazu.si (https://orcid.org/0000-0002-6543-6548),
matija.zorn@zrc-sazu.si (https://orcid.org/0000-0002-5788-018X)

1 Introduction
The Skuta Glacier (Pavšek 2004, 2007) in the Kamnik–Savinja Alps is one of the two remaining glaciers
in Slovenia, the other being the Triglav Glacier (Gabrovec et al. 2013, 2014; Triglav Čekada and Zorn 2020).
It lies in a shady cirque, around 3 hectares in size, surrounded by rock walls. In contrast to the Triglav Glacier
and the nearby Canin glaciers in Italy (Triglav Čekada, Zorn, and Colucci 2014), the past size of which
can be assessed from the mid-nineteenth century onward based on various historical images (Triglav Čekada
2018), no images going back that far are available for the Skuta Glacier.
Systematic measurements of the Skuta Glacier began in 1946 (Meze 1955; Pavšek 2007), and in 1962
the glacier also began to be photographed during regular measurements at the end of the melting season
(Košir 1976). Various cameras were used and photographs were taken from two positions: the lower edge
of the Ledine Cirque and along the hiking trail near the fork between the routes to the Savinja Pass and
the Rinka peaks, provisionally named Ob macesnu ‘ At the Larch’ (Košir 1976).
This article presents the measurements of the glacier’s perimeter and its upper edge acquired from the
photographs taken from the standpoint »At the Larch.« The results are compared against the average annu-
al temperature and the maximum seasonal snow cover depth. These two indicators have proven significant
in similar studies of the Triglav Glacier (Triglav Čekada and Gabrovec 2013).
Today’s Skuta Glacier is considered a very small glacier, or glacieret (Kumar 2011). The results of this
study can thus be compared to other glaciers of similar size, especially those that lie at lower elevations in
middle latitudes and are therefore heavily exposed to short-term climate changes (e.g., Djurović 2012; Colucci
and Žebre 2016; Gachev and Mitkov 2019; Gachev 2020).
2 Data and methods
2.1 Field measurements
The initial observations of the Skuta Glacier included permanent marking of fixed measurement points
around the glacier. At the end of each annual melting season, the glacier’s retreat from these points was
measured with a tape measure and a compass. Because the glacier lies in a cirque, most fixed measurement
points were set on its upper edge or the rock walls surrounding the cirque. Consequently, (sub)vertical retreats
were most often measured on the upper edge (Meze 1955; Košir 1976, 1986; Pavšek 2007) rather than hor-
izontal retreats, which were typically measured in similar studies of the glaciers nearby (Triglav Čekada
et al. 2012; Gabrovec et al. 2013; Colucci and Guglielmin 2015).
The (sub)vertical and horizontal retreat are published in articles covering the first four decades of mea-
surements (Gams and Kopač 1955; Meze 1955; Košir 1976, 1986). Later the retreats were so extensive that
the old fixed measurement points were no longer used. New ones were marked, but the retreats from these
points are not directly comparable with the old ones (Pavšek 2007).
In 1997 and 2003, the first tachymetric surveying of the glacier was conducted and, since 2007, field
surveys with annual geodetic measurements have been performed (Pavšek 2012).
In 2006, a steam drill was used to measure the thickness of the glacier (ice and firn). The average thick-
ness was 7 m and the maximum thickness was nearly 12 m. Its volume was estimated at just under 80,000 m
3
(Pavšek 2007).
2.2 Photography
Since 1962, the glacier has also been photographed during regular field measurements (Košir 1976). Various
cameras and positions have been used. This analysis only includes photographs taken from »At the Larch«
(Table 1, Figure 1).
Photographic material makes it possible to reconstruct the glacier’s upper edge before 1997, when the
Skuta Galcier was geodetically surveyed for the first time, and it helps to reconstruct the glacier from 1997
until the next geodetic survey conducted in 2003 as well. Even though annual geodetic surveys have been
conducted since 2007, photographs taken after 2007 were also studied for comparison.
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Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn, Changes in the Skuta Glacier (southeastern Alps) assessed …
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Table 1: Dates and photographers of the images analyzed (Figure 1).
Date Photographer
26 September 1970 Dušan Košir
22 September 1973 Dušan Košir
8 July 1982 Dušan Košir
22 September 1995 Miha Pavšek
10 September 1998 Miha Pavšek
28 October 1999 Miha Pavšek
3 July 2001 Miha Pavšek
5 October 2004 Miha Pavšek
19 October 2005 Miha Pavšek
23 September 2006 Miha Pavšek
15 October 2007 Miha Pavšek
11 September 2008 Miha Pavšek
7 September 2009 Miha Pavšek
21 September 2010 Miha Pavšek
30 September 2011 Miha Pavšek
29 August 2014 Miha Pavšek
2 October 2015 Miha Pavšek
2.3 Aerial laser scanning
In 2012, special aerial laser scanning (lidar) was performed twice on the Skuta Glacier: first on May 15th,
at the end of the accumulation season, and on September 18th, at the end of the melting season. The scan-
ning was performed using a Riegl LM5600 with a 1550 nm wavelength. The average point density was 8 points/m
2
and the flight altitude was 200 m above the glacier. In this analysis, a digital terrain model (DTM) with
a grid size 1m×1m was used, produced from the September laser scanning (Triglav Čekada et al. 2013).
On August 29th, 2014 the glacier was scanned again as part of the national aerial laser scanning of
Slovenia (Triglav Čekada and Bric 2015). This scanning was performed using a Riegl LMS-Q780 with a 1064
nm wavelength at a flight altitude of 1000 m. A point cloud with a density of 5 points/m
2
and a 1m×1m
DTM were produced as well. Because of a mild summer and previous above-average accumulation sea-
son, there was still an abundance of snow on the glacier and therefore these data were not used in the analysis.
2.4 Meteorological data
According to Košir (1976, 1986), changes in the area covered by the Skuta Glacier depend on the mean
summer air temperature, and he also established a connection with the maximum seasonal snow cover
depth. Both indicators have also proved significant in the monitoring of the Triglav Glacier (Triglav Čekada
and Gabrovec 2013).
Because no direct meteorological data are available for the Skuta Glacier, approximations of the aver-
age annual air temperature and maximum seasonal snow cover depth were calculated based on data from
nearby meteorological stations.
Meteorological data were obtained from the Slovenian Environment Agency (ARSO) online archive
(Arhiv … 2018). The nearest Slovenian meteorological station with an extended series of measurements
is the one on Mount Krvavec. Standing at an elevation of 1742 m, it has been collecting data since 1973
(marked in Figure 2 as »Krvavec 2«). It is just under 8 km as the crow flies from the Skuta Glacier. The
previous meteorological station on Mount Krvavec stood at an elevation of 1478 m (marked in Figure 2
as »Krvavec 1«). Unfortunately, these stations do not provide a complete series of average annual temperatures
and monthly snow cover depths for all the years studied. Data from the Krvavec 1 station covering the
period from 1963 to 1973 were used for the analysis.
Because the current station stands lower than the average elevation of the Skuta Glacier, as did the pre-
vious station, data from the Kredarica meteorological station at an elevation of 2514 m were used to calculate

the average annual temperature. This station is approximately 55 km from the Skuta Glacier and has com-
plete data series from 1955 onward.
The average annual temperature from Mounts Kredarica and Krvavec were adjusted (Figure 2) using the
vertical average annual temperature gradient for Zgornje Jezersko (−0.44°C/100m; Ogrin, Koželj, and Vysoudil
2016). Figure 2 shows a similar fluctuation in adjusted average annual temperatures for both stations.
To obtain a more complete series of measurements, the adjusted average temperatures from Mount
Kredarica were used as a better approximation of temperature conditions at the average elevation of the
Skuta Glacier. From 1960 to 1990, the average annual temperature on Mount Kredarica was −1.66 °C.
According to Ogrin, Koželj, and Vysoudil (2016), the average annual temperature at Zgornje Jezersko dur-
ing the same period was 5.9 °C. Based on the vertical temperature gradient between Mount Kredarica and
Zgornje Jezersko, or between the elevations of 2514 m and 894 m, the adjusted average annual tempera-
ture for Zgornje Jezersko is 5.46 °C.
Acta geographica Slovenica, 60-2, 2020
179
2005
1973 1982 1995
2015 2010
Figure 1: Some of the photographs of the Skuta Glacier from »At the Larch« used for the analysis, taken in 1973, 1982, 1995, 2005, 2010, and 2015.
Z R C S A Z U , A N T o N M E l Ik G E o G R A P h IC A l IN S T IT U T E A R C h Iv E ; F o R A U T h o R S S E E T A B l E 1

Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn, Changes in the Skuta Glacier (southeastern Alps) assessed …
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–1.0
–0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Ye a r
Kredarica Linear (Kredarica) Linear (Krvavec 2)
Corrected temperature (°C) for altitude 2070 m a.s.l.
Krvavec 2 Krvavec 1
0
100
200
300
400
500
600
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Year
Kredarica (2513 m)
Krvavec 1 (1478 m)
Krvavec 2 (1742 m)
Zgornje Jezersko together (889 m)
Maximum snow cover depth in March (cm)
Figure 2: Average annual temperatures on Mounts Kredarica and Krvavec adjusted to the average elevation of the Skuta Glacier (2070 m).
Figure 3: Maximum March snow cover depth on Mounts Kredarica and Krvavec, and at Zgornje Jezersko, based on aggregated data from the meteo-
rological stations there.

Data on snow cover depth were also obtained from the ARSO online archive (Figure 3); the data from
seven meteorological stations at Zgornje Jezersko (at elevations ranging from 876 to 912 m) were also used.
The longest time series were recorded at the site at an elevation of 889 m (1977–1985, 2006–2014), there-
fore this elevation was used as the reference elevation for Zgornje Jezersko.
From 1969 to 1970, 1995 to 1996, in 1999, from 2004 to 2007, and in 2015, concurrent changes in the
snow cover depth can be observed on Mounts Kredarica and Krvavec, and at Zgornje Jezersko in March
(Figure 3). The 1993–2014 data series for the Krvavec 2 station and the aggregated data series for the Zgornje
Jezersko stations are very similar; at the same time, maximums were also recorded on Mount Kredarica.
The precipitation and snow cover depth are reported to increase linearly with elevation (Asaoka and
Kominami 2012; Grünewald, Bühler, and Lehning 2014). Based on the linear dependence between the ele-
vation and the average snow cover depth (based on the data presented in Table 2; y is the average snow cover
depth and x is the elevation), the average snow cover depth for the Skuta Glacier was calculated (Table 2). The
maximum (March) snow cover depth calculated was 228 cm, which is 109 cm less than the snow cover depth
at Mount Kredarica.
Table 2: Average March snow cover depth from 1961 to 2016 at various meteorological stations and elevations (*calculated based on linear dependence).
Station Elevation (m) Average snow cover depth (cm)
Kredarica 2,513 337
Krvavec 1 1,478 123
Krvavec 2 1,742 112
Zgornje Jezersko 889 33
Skuta Glacier 2,070 228*
2.5 Single image interactive orientation acquisition method
The perimeter and upper edge of the Skuta Glacier were acquired from single photographs from various
years using the single image interactive orientation acquisition method, also known as monoplotting. It
requires only one photograph and a detailed DTM to calculate the orientation parameters. The method
was developed for measuring the Triglav Glacier (Triglav Čekada et al. 2011; Triglav Čekada, Bric, and
Zorn 2014). The content in the photographs is visually compared against a modern DTM projection to
obtain the best fit, in which the parameters of the external image orientation (i.e., three coordinates of the
camera’s projection center, three rotation angles, and the scale of the projected model) are searched for. If
an image or parts of it have significant radial distortions, then these can be searched for as well (Triglav
Čekada, Bric, and Zorn 2014). The basic premise, that allows us to use this method, is that there was no
significant change in the terrain around the glacier between the time when the photograph was taken and
the time when a modern DTM was created. If the interactive orientation is successful, the features seen
in the image fit to those seen on the DTM projection. This is followed by a 3D vectorization of the glac-
ier’s edge based on the projected DTM points.
In this analysis, the September 2012 DTM was applied (Figure 4). The result of the vectorization is
a continuous line showing the 3D perimeter of the glacier.
The vectorization of the Skuta Glacier was difficult because part of it is always obscured from the per-
spective photographed (the extreme left and right parts of the glacier in Figures 4 and 5). A similar challenge
was also encountered in acquiring the sizes of the Canin glaciers (Triglav Čekada, Zorn, and Colucci 2014).
The obscured part was added as follows: the glacier’s edge in the visible section of the cirque was vector-
ized from the photograph and then the vectorization of its perimeter was continued along the isohypse
in the obscured section.
By comparing the areas in three interactively oriented images, in which all three orientation angles
were »distorted« by ±0.2°, the precision of the area calculations through standard deviation can be esti-
mated at ±0.1 hectares (Barbo 2018), which corresponds to 7% of the Skuta Glacier’s area per average area
of 1.5 hectares.
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Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn, Changes in the Skuta Glacier (southeastern Alps) assessed …
182
The average elevation of the glacier’s upper edge was calculated using 30 to 160 points acquired by the
method used based on photographs in which the upper edge was visible. Some of the results at approxi-
mately ten-year intervals are shown in Figure 5.
To determine the glacier’s perimeter, the entire area covered in snow, firn, or ice was measured, and
not only the ice. The glacier’s upper edge was also determined based on the same principle.
3 Results
The area covered by the Skuta Glacier remained approximately the same between 1970 and 2015 (between
one and two hectares; Table 3, Figure 6). If the calculations made in this study are compared with the field
measurements, it can be established that the results differ by up to 0.4 hectares, which corresponds to just
under a third of the glacier’s area. The method used yielded relatively smaller areas than those established
through field measurements; the only exceptions were the results for 2007 and 2015.
Using this method, the largest area was measured for 1982; the photograph from this year shows a heav-
ily snowed-in glacier and its surroundings (Figure 1). The entire area of the glacier in the cirque and the
snowed-in tongue outside it was measured, which in fact covers not only the glacier, but also the adjacent
snowfield. It also needs to be taken into account that the photograph was taken more than two months
before the end of the melting season (i.e., in early July; Table 1).
There are no major differences in the glacier’s size between the start and end of the period studied,
but significant changes can be observed in the elevation of its upper edge and thus its thickness. During
the period studied, the upper edge elevation decreased by nearly 40 m (Table 3, Figure 5). The elevation
of the glacier’s upper edge fluctuates significantly from year to year because the glacier’s thickness great-
ly depends on the snow conditions and when the measurements are conducted in an individual year in
relation to the end of the melting season. A distinct decrease in the elevation of the upper edge can be observed
from the early 1970s to the end of the 1990s.
Figure 4: The Skuta Glacier in 2010 with a vectorized edge and a matching DTM projection.
M Ih A P A v Š E k , Z R C S A Z U , A N T o N M E l Ik G E o G R A P h IC A l IN S T IT U T E A R C h Iv E

Acta geographica Slovenica, 60-2, 2020
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Figure 5: Elevation of the glacier’s upper edge in 1973, 1982, 1995, 2006, and 2015 projected onto a 2015 photograph.
Legend
1973
1982
1995
2006
2015
Content by: Patricija Bar o
Source: GIAM
b
M Ih A P A v Š E k , Z R C S A Z U A N T o N M E l Ik G E o G R A P h IC A l IN S T IT U T E A R C h Iv E S

Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn, Changes in the Skuta Glacier (southeastern Alps) assessed …
184
Changes in the glacier definitely reflect the increase in average annual temperatures (Figures 7 and 8).
During the period studied, the average annual temperature at the glacier’s average elevation increased from
approximately −0.2 °C in 1963 to 1.7 °C in 2015. It is not only the increase of nearly 2 °C that is impor-
tant, but also the temperature transition above the freezing point.
In addition to temperature, changes in the glacier are also influenced by the snow cover depth. In addi-
tion to falling snow, the majority of snow accumulates on the Skuta Glacier in the form of avalanches and
to a smaller extent as drifting snow.
A comparison of the Skuta Glacier’s area and the average annual temperature after 2003 shows that
from 2008 to 2010 the glacier’s area increased when the average annual temperatures were below the tem-
perature increase trend line. However, from 2004 to 2005, when the average annual temperatures were also
lower than the trend, the area was shrinking (Figure 7). The difference between the two periods results
from the differences in the maximum seasonal snow cover depths on the glacier in June (Figure 9).
An even more direct connection between the average annual temperature and the June snow cover depth
is reflected by the changes in the average elevation of the glacier’s upper edge (Figures 8 and 10). If the aver-
age temperatures are low, this makes it easier for the snow to remain on the upper edge until the end of the
melting season. The impact of the snow cover depth on the elevation of the glacier’ s upper edge can be observed
in 2009 and 2010. The year 2009 was characterized by a large amount of snow and a low average tempera-
ture and 2010 was marked by a low snow cover depth and a low average temperature. Consequently, the glacier’ s
upper edge in 2009 was higher than in 2010. The upper edge also lowered in 1998 and 1999, when the aver-
age annual temperatures were slightly below the temperature trend line and there was very little snow in June.
4 Discussion
Because the Skuta Glacier is confined in a narrow cirque, it has managed to retain its area over the past
half-century. However, this stability does not apply to its upper edge, where significant changes have been
observed (Table 3, Figures 5 and 6).
Table 3: Area of the Skuta Glacier and the average elevation of its upper edge between 1950 and 2015 (*tachymetric survey; **survey in early July).
Year Area based on photographs Area based on field measurements Average elevation of upper edge
(hectares) (hectares) based on photographs (m)
1950 – 2.8 –
1970 1.8 2,153
1973 2.3 2,151
1982 4.2** – 2,153
1989 1.1
1995 1.8 – 2,138
1997 1.5*
1998 1.4 – 2,114
1999 1.1 – 2,109
2001 1.0 – 2,129
2004 1.6 – 2,114
2005 1.0 – 2,100
2006 1.3 – 2,111
2007 1.5 1.1* 2,112
2008 1.0 1.4* 2,119
2009 1.4 1.8* 2,145
2010 1.7 1.8* 2,124
2014 2.1 2.1* 2,133
2015 1.6 1.4* 2,115
Figure 6: Changes in the Skuta Glacier’s area in 1973, 1982 (*survey in early July), 1995, 2006, and 2015 measured using the single image interactive
orientation acquisition method.p

Acta geographica Slovenica, 60-2, 2020
185
N
Legend
2015
2006
1995
1982*
1973
Content by: Patricija Barbo
Map by: Manca Volk Bahun
Source: GIAM, MOP 2014, MK 2018
© 2020, ZRC SAZU, Anton Melik Geographical Institute
0 50 100m

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186
–1
– . 0 5
0
0 5 .
1
15 .
2
25 .
3
00 .
05 .
10 .
15 .
20 .
25 .
30 .
35 .
4 0 .
45 .
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Area (ha)
Year
Area: Interactive orientation method ha ( ) Area: Field measurement ha ( )
Corrected mean annual temperature °C ( ) Linear (Corrected mean annual temperature °C ) ( )
Mean annual temperature (°C)
–1
– . 0 5
0
05 .
1
15 .
2
25 .
3
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Mean annual temperature (°C)
2070
2080
2090
2100
2120
21 0 1
2130
2140
2150
2160
2170
Altitude a.s.l. (m)
Year
Average upper edge altitude m ( ) Corrected mean annual temperature °C ( )
Linear (Average upper edge altitude m ) ( ) Linear (Corrected mean annual temperature °C ) ( )
Figure 7: Areas covered by the Skuta Glacier measured using the single image interactive orientation acquisition method and field surveys and their
comparison with average annual temperatures at an elevation of 2070 m, or the average elevation of the Skuta Glacier.
Figure 8: Annual elevations of the Skuta Glacier’s upper edge determined with the single image interactive orientation acquisition method and their
comparison with average annual temperatures at an elevation of 2070 m, or the average elevation of the Skuta Glacier.

Acta geographica Slovenica, 60-2, 2020
187
Area: Interactive orientation method ha ( ) Area: Field measurement ha ( )
Corrected maximum snow cover depth cm ( ) Linear (Corrected maximum snow cover depth cm ) ( )
Maximum snow cover depth in June (cm)
0
50
100
150
200
250
300
00 .
05 .
10 .
15 .
20 .
25 .
30 .
35 .
40 .
45 .
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Area (ha)
Year
Year
Average upper edge altitude m ( ) Corrected maximal snow cover depth cm ( )
Linear (Average upper altitude m ) ( ) edge Linear (Corrected maximal snow cover depth cm ) ( )
0
50
100
150
200
250
300
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
2070
2080
2090
2100
2120
21 0 1
2130
2140
2150
2160
2170
Altitude a.s.l. (m)
Maximum snow cover depth in June (cm)
Figure 9: Areas covered by the Skuta Glacier measured using the single image interactive orientation acquisition method and field surveys, and their
comparison with the maximum seasonal snow cover depth at an elevation of 2070 m, or the average elevation of the Skuta Glacier, in June.
Figure 10: Annual elevations of the Skuta Glacier’s upper edge determined with the single image interactive orientation acquisition method and their
comparison with the maximum seasonal snow cover depth at an elevation of 2070 m, or the average elevation of the Skuta Glacier, in June.

Mihaela Triglav Čekada, Patricija Barbo, Miha Pavšek, Matija Zorn, Changes in the Skuta Glacier (southeastern Alps) assessed …
The results of this study are based on the single image interactive orientation acquisition method (Triglav
Čekada, Bric, and Zorn 2014), which has already been successfully applied to measurements of the Triglav
Glacier (Triglav Čekada and Gabrovec 2013) and Canin glaciers (Triglav Čekada, Zorn, and Colucci 2014)
in the Julian Alps. These measurements slightly deviate from the field surveys (Table 3) due to the poor-
er accuracy of the images compared to the field measurements, as well as problems in interpreting images
due to poor contrast or difficulties distinguishing between snow or ice and calcareous debris. Mostly the
single image interactive orientation acquisition method for the Skuta Glacier gives underestimated results
compared to the area measured using tachymetric surveying. Nonetheless, the method used is useful for
determining glacier changes because the size of glaciers can be measured based only on amateur photographs
taken by non-metric cameras. First and foremost, the method is useful for very small glaciers, which can
be documented in full in a single photo.
The data acquired for the Skuta Glacier can be compared to other very small glaciers in the south-
eastern Alps (Triglav Čekada et al. 2012; Colucci and Žebre 2016; Lipar et al. 2020; Triglav Čekada and
Zorn 2020), southeastern Europe (Grunewald and Scheithauer 2010; Hughes 2010, 2018; Djurović 2012;
Gachev, Stoyanov, and Gikov 2016; Gachev 2020), the Pyrenees (González Trueba et al. 2008), and else-
where around the globe (DeBeer and Sharp 2009; Shahgedanova et al. 2012).
What all these studies have in common is that they connect the decrease in glaciers’ size with the increase
in the average annual temperature, the average temperature during the melting season, or average sum-
mer temperatures, which in reference to the Skuta Glacier has already been mentioned by Košir (1976,
1986). The likely connection between average temperatures and the snow cover depth on glaciers and snow-
fields in Slovenia was already discussed by Manohin and Gams (1959). In turn, contemporary authors,
such as Grunewald and Scheithauer (2010), report that periods with above-average winter precipitation
and cold summers can even »stabilize« very small glaciers or help them grow temporarily. This is also sug-
gested by the data for the Skuta Glacier, which usually does not grow on the account of ice, but snow. On
the other hand, Gachev and Mitkov (2019) associate the shrinking of very small glaciers with the increase
in summer precipitation.
Over the past half-century, similar trends as elsewhere have been observed on very small glaciers in
the southeastern Alps. The area covered by the Triglav Glacier halved from the mid-1980s to the early 1990s
(it decreased from 10 to just over 4 hectares), and over the past two decades it has maintained an area between
0.5 and 1 hectares (Triglav Čekada and Gabrovec 2013). From the 1970s to the end of the century, the two
Canin glaciers also halved in size, which was also assessed using the single image interactive orientation
acquisition method (Triglav Čekada, Zorn, and Colucci 2014). In southeastern Europe, the size of the Debeli
Namet Glacier in Montenegro, which lies at a similar elevation as the Skuta Glacier, has more than halved
since the 1980s (Djurović 2012). In turn, the size of the Snežnik Glacier in Bulgaria, which lies at a simi-
lar elevation as the Triglav Glacier, more than halved from the early 1960s to the mid-1990s (Gachev, Stoyanov,
and Gikov 2016). The current average annual temperature on the Debeli Namet Glacier is above 0 °C
(Grunewald and Scheithauer 2010), just like on the Skuta Glacier. Over the past decade, both the Debeli
Namet and Snežnik glaciers have more or less retained their size: the size of the former fluctuates between
1.5 and 3.0 hectares, and that of the latter between just under 0.4 and just over 0.6 hectares. Their relative
stability is associated with the strong influence of terrain on the microclimate (Gachev, Stoyanov, and Gikov
2016; Gachev 2020). DeBeer and Sharp (2009) also establish that terrain influences how very small glaci-
ers respond to climate change. Grunewald and Scheithauer (2010) add that in the concluding stages of glacial
degradation the impact of climate factors relatively decreases, whereas the impact of terrain increases. According
to the measurements conducted on both Slovenian glaciers (i.e., the Skuta Glacier and the Triglav Glacier;
Triglav Čekada and Zorn 2020), these findings may apply to Slovenia’s very small glaciers.
5 Conclusion
Changes in the Skuta Glacier since the early 1970s were studied based on seventeen photographs taken
from the same location using various non-metric cameras. The area covered by the glacier and the ele-
vation of its upper edge were determined using the single image interactive orientation acquisition method.
During the period studied (1970–2015), the glacier’s size did not change significantly, whereas the aver-
age elevation of the glacier’s upper edge decreased by as much as nearly 40 m.
188

Because there is no meteorological station near the Skuta Glacier, data from nearby stations were used
to determine the average annual temperature and maximum seasonal snow cover depth on the glacier.
The maximum seasonal snow cover depth at the end of the accumulation season has proven vital for pre-
serving the glacier’s thickness.
ACKNOWLEDGMENTS: The authors acknowledge the financial support from the Slovenian Research
Agency research project funding Predictive analytics based on location-associated context enrichment (J2-
8176) and research core funding Geography of Slovenia (P6-0101). The authors would like to thank everyone
involved in the measurements of the Skuta Glacier, without whom this study would not have been possible.
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