ACTA GEOGRAPHICA
SLOVENICA
GEOGRAFSKI
ZBORNIK
2021
61
2
0 1 0 1 6 6 1 8 5 1 7 7 9
ISSN 1581-6613
ACTA GEOGRAPHICA SLOVENICA 
•
GEOGRAFSKI ZBORNIK 
•
61-2 
•
2021
ACTA GEOGRAPHICA SLOVENICA
GEOGRAFSKI ZBORNIK
61-2 • 2021
Contents
Đorđije V a sil je Vić , Milica Be g a n , Miroslav Vu jič ić , Thomas Ho se , u glješa sTa n k o V
Does geosite interpretation lead to conservation? A case study of the Sićevo Gorge (Serbia) 7
g abrijela Po Po Vić , Dragiša sTa n u jk ić , Predrag MiMo Vić , g oran Mil o V a n o Vić ,
Darjan k a r a Ba š e Vić , Pavle Br z a k o Vić , a leksandar Br z a k o Vić An integrated SWOT – extended PIPRECIA model for identifying key determinants of tourism
development: The case of Serbia 23
r obert k a l Ba r c z y k , e liza k a l Ba r c z y k
Precipitation variability, trends and regions in Poland: Temporal and spatial distribution
in the years 1951–2018 41
ivana c r l je n k o , Matjaž g e r š ič
A comparison of the beginnings of exonym standardization in Croatian and Slovenian 73
Tadej Br e z in a , jernej Tir a n , Matej o g r in , Barbara l a a
COVID-19 impact on daily mobility in Slovenia 91
Maruša g o l u Ža , Maruška šu Bic -k o V a č , Drago k o s , David Bo l e
How the state legitimizes national development projects: The Third Development Axis
case study, Slovenia 109
Tin l u k ić , Tanja Mic ić Po n jig e r , Biljana Ba s a r in , Dušan s a k u l s k i,
Milivoj g a Vr il o V , s lobodan Ma r k o Vić , Matija z o r n , Blaž k o Ma c ,
Miško Mil a n o Vić , Dragoslav P a Vić , Minučer Me s a r o š , n emanja
Ma r k o Vić , u roš Du r l e Vić , c ezar Mo r a r , a leksandar Pe Tr o Vić Application of Angot precipitation index in the assessment of rainfall erosivity:
Vojvodina Region case study (North Serbia) 123
janij o Bl a k , Mira k o Bo l D, Mojca š r a j
The influence of climate change on discharge fluctuations in Slovenian rivers 155
Vladimir s To ja n o Vić , Dubravka Mil ić , s anja o Br a Do Vić , jovana V a n o V a c ,
Dimitrije r a Diš ić The role of ecotourism in community development: The case of the Zasavica Special Nature
Reserve, Serbia 171
Marko V . Mil o š e Vić , Dragoljub š Tr Ba c , jelena ć a l ić , Milan r a Do V a n o Vić Detection of earthflow dynamics using medium-resolution digital terrain models: Diachronic
perspective of the Jovac earthflow, Southern Serbia 187
naslovnica 61-2_naslovnica 49-1.qxd  30.11.2021  13:58  Page 1

ACTA GEOGRAPHICA
SLOVENICA
GEOGRAFSKI
ZBORNIK
2021
61
2
0 1 0 1 6 6 1 8 5 1 7 7 9
ISSN 1581-6613
ACTA GEOGRAPHICA SLOVENICA 
•
GEOGRAFSKI ZBORNIK 
•
61-2 
•
2021
ACTA GEOGRAPHICA SLOVENICA
GEOGRAFSKI ZBORNIK
61-2 • 2021
Contents
Đorđije V a sil je Vić , Milica Be g a n , Miroslav Vu jič ić , Thomas Ho se , u glješa sTa n k o V
Does geosite interpretation lead to conservation? A case study of the Sićevo Gorge (Serbia) 7
g abrijela Po Po Vić , Dragiša sTa n u jk ić , Predrag MiMo Vić , g oran Mil o V a n o Vić ,
Darjan k a r a Ba š e Vić , Pavle Br z a k o Vić , a leksandar Br z a k o Vić An integrated SWOT – extended PIPRECIA model for identifying key determinants of tourism
development: The case of Serbia 23
r obert k a l Ba r c z y k , e liza k a l Ba r c z y k
Precipitation variability, trends and regions in Poland: Temporal and spatial distribution
in the years 1951–2018 41
ivana c r l je n k o , Matjaž g e r š ič
A comparison of the beginnings of exonym standardization in Croatian and Slovenian 73
Tadej Br e z in a , jernej Tir a n , Matej o g r in , Barbara l a a
COVID-19 impact on daily mobility in Slovenia 91
Maruša g o l u Ža , Maruška šu Bic -k o V a č , Drago k o s , David Bo l e
How the state legitimizes national development projects: The Third Development Axis
case study, Slovenia 109
Tin l u k ić , Tanja Mic ić Po n jig e r , Biljana Ba s a r in , Dušan s a k u l s k i,
Milivoj g a Vr il o V , s lobodan Ma r k o Vić , Matija z o r n , Blaž k o Ma c ,
Miško Mil a n o Vić , Dragoslav P a Vić , Minučer Me s a r o š , n emanja
Ma r k o Vić , u roš Du r l e Vić , c ezar Mo r a r , a leksandar Pe Tr o Vić Application of Angot precipitation index in the assessment of rainfall erosivity:
Vojvodina Region case study (North Serbia) 123
janij o Bl a k , Mira k o Bo l D, Mojca š r a j
The influence of climate change on discharge fluctuations in Slovenian rivers 155
Vladimir s To ja n o Vić , Dubravka Mil ić , s anja o Br a Do Vić , jovana V a n o V a c ,
Dimitrije r a Diš ić The role of ecotourism in community development: The case of the Zasavica Special Nature
Reserve, Serbia 171
Marko V . Mil o š e Vić , Dragoljub š Tr Ba c , jelena ć a l ić , Milan r a Do V a n o Vić Detection of earthflow dynamics using medium-resolution digital terrain models: Diachronic
perspective of the Jovac earthflow, Southern Serbia 187
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Acta geographica Slovenica, 61-2, 2021, 187–206
DETECTION OF EARTHFLOW DYNAMICS
USING MEDIUM-RESOLUTION DIGITAL
TERRAIN MODELS: DIACHRONIC
PERSPECTIVE OF THE JOVAC
EARTHFLOW, SOUTHERN SERBIA
Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović
Jovac earthflow, head scarp zone.
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
188
DOI: https://doi.org/10.3986/AGS.9818
UDC: 911.2:551.435.62(497.11-13)
COBISS: 1.01
Marko V . Milošević
1
, Dragoljub Štrbac
1
, Jelena Ćalić
1
, Milan Radovanović
1,2
Detection of earthflow dynamics using medium-resolution digital terrain models:
Diachronic perspective of the Jovac earthflow, Southern Serbia
ABSTRACT: The paper presents and discusses the landslide research procedure related to the topogra-
phy before and after its occurrence, using the comparative analysis of two medium-resolution digital terrain
models. The case study is the Jovac mega-landslide – the largest landslide to occur in Serbia in the last
100 years, active for three days in February 1977. The indicators used to determine the volume and move-
ment mechanism were the spatial distribution of elevation differences within the two digital terrain models
(DTM), and the analysis of geomorphological features before the landslide. The obtained elevation dif-
ferences allowed the definition of the approximate landslide volume: 11.6 × 10
6
m
3
. All the data obtained
indicate that the movement mechanism falls into the category of earthflow.
KEY WORDS: landslide, earthflow, GIS analysis, Jovac, Serbia
Zaznavanje dinamike premikanja zemeljskih gmot z uporabo digitalnih modelov
višin srednje ločljivosti: Diakronična perspektiva plazu Jovac, južna Srbija
POVZETEK: Prispevek predstavlja in obravnava postopek raziskovanja zemeljskih plazov, ki se nanaša
na topografijo pred nastankom procesa in po njem, s primerjalno analizo dveh digitalnih modelov tere-
na srednje ločljivosti. Študija primera je mega zemeljski plaz Jovac, ki je največji plaz v Srbiji zgodil v zadnjem
stoletju in je bil aktiven tri dni februarja 1977. Kazalniki, ki določajo prostornino in mehanizem gibanja,
so prostorska porazdelitev višinskih razlik v obeh digitalni modeli terena (DTM), pa tudi analiza pred-
hodnih geomorfoloških značilnosti. Dobljene višinske razlike so omogočile določitev približne prostornine
plazu: 11,6 × 10
6
m
3
. Vsi pridobljeni podatki kažejo, da mehanizem gibanja spada v kategorijo zemljinskih
tokov.
KLJUČNE BESEDE: zemeljski plaz, drobirski tok, analiza DMR, Jovac, Srbija
The article was submitted for publication on March 22
nd
, 2021.
Uredništvo je prejelo prispevek 22. marca 2021.
1
Serbian Academy of Sciences and Arts, Geographical Institute Jovan Cvijić, Belgrade, Serbia
m.milosevic@gi.sanu.ac.rs (https://orcid.org/ 0000-0001-5188-7260), d.strbac@gi.sanu.ac.rs
(https:/ /orcid.org/ 0000-0001-9946-7978), j.calic@gi.sanu.ac.rs ( https://orcid.org/ 0000-0002-7271-5561),
m.radovanovic@gi.sanu.ac.rs (https://orcid.org/0000-0002-9702-3879)
2
South Ural State University, Institute of Sports, Tourism and Service, Chelyabinsk, Russia
m.radovanovic@gi.sanu.ac.rs (https://orcid.org/0000-0002-9702-3879)
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1 Introduction
The article deals with earthflow as a specific form/process of landslides from the perspective of changing
topography, within a case study of the Jovac earthflow in south-eastern Serbia. Landslides, as one of the
most dynamic processes, have been thoroughly studied in the last decades, especially with the rapid devel-
opment of geomorphometric tools. Among the most cited and important references are the works of Varnes
(1978; 1984) on landslide hazard zonation, Cruden (1991), Cruden and Varnes (1996) on landslide types,
and Hungr, Leroueil and Picarelli (2014) on landslide typification. Cruden’s (1991) definition is accepted
by the institutions which defined the international standards in landslide research, such as The international
geotechnical societies’ UNESCO working party for world landslide Inventory (1993), and the International
Association for Engineering Geology and the Environment (IAEG) (UNESCO working…1993). Furthermore,
the above-mentioned references indicate a high degree of diversification of landslides depending on the
type of movement and the type of material. Within this typology, the combination of relatively high water
content within the small-grained material indicates the landslide category of earthflow, as a subgroup in
the landslide classification system. Hungr, Leroueil and Picarelli (2014) define earthflow material as a cohe-
sive, plastic, clayey soil material, often mixed and remoulded with the Liquidity Index below 0.5. Keefer
and Johnson (1983) state that many earthflows contain fragments of material in various stages of remould-
ing and may carry granular clasts. The IGS Multilingual Landslide Glossary (1993) recognizes the term
»flow« (not earthflow) and explains that the distribution of velocities in the displacing mass is similar to
that in a viscous fluid. Valuable theoretical background for earthflows is provided by Urciuoli et al. (2016),
who explain the relationship between morphological aspects, kinematic behaviour and slope stability con-
ditions.
Digital terrain models (DTMs) are a resource of high importance within landslide detection and research.
(Mahalingam and Olsen 2016). Jaboyedoff et al. (2012) see the role of DTM in:
• mass movement detection and characterization,
• hazard assessment and susceptibility mapping,
• modelling, and
• monitoring.
The resolution of a DTM is one of the crucial properties affecting the quality of research results (Lee
et al. 2004; Hrvatin and Perko 2005; Santini et al. 2009). In the early period of DTM development, it was
assumed that higher resolution would automatically lead to better results (Dietrich and Montgomery 1998).
However, recent studies show that resolutions of 2 m, 5 m and 10 m do not necessarily provide more accu-
rate results (Mahalingam and Olsen 2016; Chen et al. 2020). In some cases with quite high resolution, the
DTM may also contain irrelevant data (Tarolli and Tarboton 2006). These can blur the key influencing
factors related to sliding during further processing. Examples of this are microtopographic details creat-
ed by subsequent denudation of the landslide body or small-scale rockfalls in the scarp zone. Therefore,
the selection of the optimal DTM resolution must consider the dimensions of the landslide, as well as the
context of the analysis (McKean and Roering 2004; Claessens et al. 2005).
Landslide detection using DTM was one of the main aims of our research which was conducted in
several time frames. A time frame refers to a state of the topographic surface at the time of the analysis.
Performing two or more analyses (assuming that the intervening period included an observable change)
provided the insight into the temporal dynamics of the process (Table 1).
Table 1: Landslide detection methods using a Digital Terrain Models (DTM).
Time frame Detection method Detected features
One time frame Visual interpretation of DTM Landslide outlines and morphometric features of the landslide
Automated interpretation of DTM topographic surface
DTM
More time frames Detection of elevation differences Landslide outlines, dimensions, morphometric features of the
before and after the landslide landslide topographic surface, depletion zone, accumulation
(two DTMs) zone, movement mechanism, monitoring
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
Within a time frame, the detection process can be done by two methods: visual interpretation and/or
automated recognition. In our case, the visual method combined with fieldwork was the starting point
for determining landslide outline (Ardizzone et al. 2007; Amundsen et al. 2010; Guzzetti et al. 2012). Visual
interpretation of DTMs relies on hillshade, the generated contours, and the slope of the topographic sur-
face (Van Den Eeckhaut et al. 2007; Schulz 2007; Đomlija 2018). This method of landslide determination
is very subjective. In contrast, an objective landslide identification method is based on statistical analyses
of DTM-generated morphometric parameters (curvature, surface roughness), which can be used to auto-
matically determine landslide contours (Tarolli, Sofia and Dalla Fontana 2012).
Two or more time-frames recorded within the DTMs allow the application of quantitative methods
in defining the outline (boundaries), approximate volume estimation, identification of depletion and accu-
mulation zones, and monitoring of landslide dynamics. The spatial distribution of colluvium can indicate
the mechanism of movement (Corsini еt аl. 2009; Fernández et al. 2011; 2017; Giordan et al. 2013). The
work of Conoscenti et al. (2015) is an example of the use of multiple time-frames in DTM analyses. A poten-
tial drawback of DTM as a method of landslide detection in general is that the DTM resolution in the analysis
phase is usually limited by the pre-sliding input data. In our case, lower data resolution can be expected
because the topographic data acquisition took place about 10 years before the landslide event, when map-
ping methods were not sophisticated as today.
The aim of this article is to determine whether a medium-resolution DTM (sensu, Gigović 2010; Table 2)
can be a reliable data source for landslide studies, given the current era of LiDAR dominance. Our hypoth-
esis is that a medium-resolution DTM can prove to be sensitive enough to determine landslide outlines,
areas and volumes, as well as reconstruct their movement mechanisms. In this study, two DTMs of the
same area are analysed – one is before and one after a landslide, created by applying two different meth-
ods. The article describes the details of the superposition procedure applied in order to avoid the systematic
errors in determining the elevation differences. In the subsequent analysis, it is possible to define the move-
ment mechanism based on the comparison of the paleo-topography and the present topography of the
Jovac landslide.
Table 2: DTM resolutions (after Gigović 2010).
Resolution Horizontal distance of elevation points
In meters In arc seconds
Low 900–90 30–3
Medium 90–30 30–1
High 30–10 1–0.3
Very high 10–1 0.3–0.03
2 Study area and basic geological setting
The Jovac landslide is located in the villages of Jovac and Ostrovica (Vladičin Han municipality) in south-
eastern Serbia (N 44.64°, E 22.003°). The mountainous area within the altitude range 400–800 m hosts the
catchment area of the Jovačka Reka River, the left tributary of the Južna Morava River (Figure 1). The cur-
rent average precipitation average is about 740 mm, with the peaks in June and May.
Geologically, the study area is located on the southwestern edge of the Eurasian Plate. According to
Prelević et al. (2005), the closure of the Neotethys basin and the collision of the Eurasian Plate with the
African Plate triggered large-scale volcanism in early Cenozoic (Cvetković, Šarić and Mladenović 2019).
One of the eruption points was located in the zone of the Grot and Oblik peaks (Vukanović et al. 1970),
7 km west of the present landslide (Figure 1). Pyroclastic material was deposited in the area within the dacite
lava eruption. During the Miocene, the lower parts of the drainage area were part of a lacustrine basin
where terrigenous sediments were deposited (Vukanović et al. 1970; Babović et al. 1977; Jovanović and
Novković 1988). The combination of these lithological components created a landslide-prone setting in the
area. Landslide activation occurred in February 1977 and destroyed 70 households in the villages of Jovac
and Ostrovica (Petrović and Stanković 1981).
190
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Acta geographica Slovenica, 61-2, 2021
191
2.1 Previous research
Two papers have already been published on the genesis and morphometry of this landslide (Lazarević 1977;
Petrović and Stanković 1981), giving dimensions of 3 km
2
area, 50 m average width and 150 × 10
6
m
3
vol-
ume. Both described the movement mechanism as a typical landslide, using the visual observation and
field mapping. Review papers mentioning the Jovac landslide mostly refer to the primary references men-
tioned (Jevremović, Sunarić and Kostić 2011; Pavlović et al. 2012). Lazarević (1977) defined the Jovac landslide
as translational and determined its area to be 1.52km
2
. Interestingly he found that there was no synchronized
movement of the entire landslide body, but rather that the upper part moved first, while the middle and
lower parts moved subsequently. Petrović and Stanković (1981) estimate the average depth of 50 m and
the volume of 150 × 10
6
m
3
. They do not explicitly mention the mechanism of movement but their figure
shows a translational landslide character (see Figure 11A).
3 Data sources and methods
The aim of the research was to determine the precise outline (boundaries), area, volume and movement
type of the Jovac landslide by analysing the topographic data from both, the pre-activation period and the
resulting landform after the landslide process was complete. The most accurate data source available for
the period before the landslide are the classical topographical maps at 1 : 25,000 published in 1971. The
contour lines of the 1 : 25K maps were digitized in detail (contour interval 10 m, additional 5 m and 2.5 m)
to subsequently create a 30×30m DTM referring to the year 1971, in UTM 34N. The accuracy of the obtained
DTM based on digital contour lines from the cartographic records is 2.2 m for TIN interpolation method
4719000
4722000
4725000
576000 579000 582000 585000
 
Ao
D
Do C
Co
B
Bo
A
Oblik
Grot
 
 
Jovačka reka River
46
44
42
20 22
Jovac
landslide
North
Macedonia
Albania
Romania
S E R B I A
012 
km
Scale: 1:90.000
Content by: Marko V. Milošević
Map by: Marko V. Milošević
Source: SRTM
© 2021, Geographical Institute »Jovan Cvijić« SASA
Pro%les
Landslide lakes
Cenozoic igneous rocks
Jovačka Reka catchment area
Jovac landslide
Legend
Figure 1: Situation map of the study area (profiles refer to figures 10 and 11).
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
192
(Govedarica and Borisov 2011). According to the 1971 map, forest vegetation covered only 12% of the stud-
ied area (in total), in 13 separate fragments; therefore, we do not consider that it affected the accuracy of
the data obtained by the photogrammetric method.
For the post-slide period, we used an SRTM DTM 30 × 30 m raster referring to the year 2000. To allow
the comparison between the two datasets, the final resolution of 30 × 30 m raster cell (pixel) resolution was
accepted for the analysis
3.1 Calculation and analysis of elevation differences
Raster arithmetic was used to calculate the elevation differences. In the first overlap of two DTMs, the 1971
elevations were subtracted from the 2000 elevations. The analysis of the elevation differences allowed the
III
fferences
–
Elevation  di
calculation
C = B A
Previous research
1:25K Topo maps SRTM
I
– Pre sliding DTM
A
II
– Post sliding DTM
B
Contour data SRTM data
A
30 m DTM raster
B
30 m DTM raster
Elevation di ferences raster f
IV
f Elevation di ferences
data analysis
Systematic di ferences data f
V
f Landslide elevation di ferences
Landslide elevation di ferences fd a t a
VI
Geomorphological analysis
Landslide borders
approx. data
Figure 2: Workflow.
61-2_acta49-1.qxd  30.11.2021  13:55  Page 192

distinction between the sliding and non-sliding (stable) parts of the studied area, which led to the deter-
mination of the exact boundary of the landslide.
The non-sliding area was subjected only to statistical analysis of elevation differences, while the slid-
ing area was subjected to geomorphological analysis. The preliminary delineation between these two units
was based on cartographic sources, literature, and fieldwork. The size ratio between the units is approxi-
mately 1 : 3 (sliding area 1770 pixels; non-sliding area 4878 pixels). The objective of the statistical analysis
of the elevation differences of the non-sliding area was to determine the quality of the overlap of two DTMs
used, while the task of the geomorphological analysis was to determine the characteristics and consequences
of the sliding process.
3.2 Test of the overlap quality of DTMs
It is assumed that the non-sliding area was not subject to any influences that would significantly change
its elevation. Consequently, the comparison of pre- and post- elevation values should be possible. The char-
acteristics and spatial distribution of the differences would indicate whether there are systematic errors
in the overlap of two DTMs obtained using the different data sources.
The total number of pixels (in the non-sliding area) for which the elevation differences were analysed
is 4878, i.e. 146,340 m
2
. The distribution of the obtained elevation differences is shown in Figure 3.
The arithmetic mean of the elevation differences between the two DTMs is x
–
= 3.940 m, while the stan-
dard deviation is σ=4.331m. The standard deviation is a measure of the quality of the overlap (i.e. agreement
of the data).
Two tests of overlap of two DTMs were performed in the following way: One of the models was shift-
ed by one pixel (30 m) with respect to the other model. The displacement had four directions – N, E, S,
W . The data on the mean (x
–
) and standard deviation (σ) of the elevation differences for each movement
are given in Table 3. Comparison of the standard deviation values of vertical differences shows that the
deviation for the initial model is the smallest, which means that the overlap was correct.
Acta geographica Slovenica, 61-2, 2021
193
Elevation dif erences (m) f
– . 200 – . 100 00 . 10 0 . 20 0.3 . 0 0
Number of pixels
0
300
400
100
200
500
600
Figure 3: Distribution of elevation differences for the non-sliding (stable) area.
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
Definite values of elevation differences were obtained by subtracting the value of 4 m in the post-sliding
DTM in relation to the pre-sliding DTM. As mentioned above, the value of 4 m (x
–
= 3.940) was taken as the
value of the systematic error.
4 Results
4.1 Paleotopography
Analysis of the pre-slide topographic surface (1971 topographic map) revealed colluvial (slope) and flu-
vial morphogenetic relief types, determined by lithological composition. The indicator for the recognition
of colluvial forms are the contour distances which at some places do not regularly follow the contour inter-
vals. Rogers and Chung (2016) suggest that the heterogeneous contour intervals on narrow and elongate
surfaces may indicate earthflows. In the case of Jovac, the colluvial traces were present only in the zone
of volcanoclastic sediments, mainly in the middle and upper part of the slope (Figure 4). Lazarević (1977)
pointed out the signs of former sliding by noting that the pond at the Jezero locality (meaning »lake« in
Serbian language) is located in a depression formed during an earlier sliding phase.
This former hydrological feature with a size of 2345 m
2
(45 × 50 m in SW–NE direction), is visible on
the 1971 topographic map. Our field research results show that there was another pond in the hamlet Deda
Dorinci, called Cekino Jezero or Cekina Bara (pond / swamp). Petrović and Stanković (1981) indirectly
confirm this by listing the morphological elements of the slope that were present before the activation of
the Jovac landslide. They note that the »middle part of the present landslide was subject to dynamic changes,
inversely inclined, with microdepressions, rounded hillocks and steep sides,« – features typical for land-
slides. In the central part of the slope there were hillocks of up to 10m relative height, depressions and landslide
terraces of different heights.
Fluvial landforms were present only in the catchment area of Manastirski Potok, which extended from
the mouth to the Jovačka River (at 400 km
2
. The lower course of the Manastirski Potok, carved a 40 m deep
gorge in pyroclastics. The valleys of the upstream tributaries are carved in volcanoclastic material with
morphological traces of sliding processes.
The longitudinal profile of a stream is one of the indicators of its morphological stage of development.
In the case of Manastirski Potok, the profile is not parabolic (as it would be in a balanced state), but uni-
formly sloping (Figure 5), indicating an early morphogenetic phase and a  possible imprinting by
a paleo-(colluvial)-relief. The lateral tributary valleys were relatively shallow, with maximum depths up
to 10 m, with inherited colluvial landforms – hillocks, depressions, sliding terraces. The hydrographic net-
work consisted only of occasional streams, with a total length of 2910 m.
4.2 Predispositions for the development of landslides
There were three main predispositions for the landslide process on the right valley side of the Jovačka Reka
River:
• lithological composition,
• morpho-hydrographic conditions: a) surface runoff areas and b) endorheic areas, and
• human impact.
194
Table 3: Arithmetic means and standard deviations of the elevation differences during the overlap test.
Pixel movement direction x
–
σ
North 8.356 5.734
East 0.748 5.082
South –0.490 6.454
West 7.091 6.567
Initial value 3.940 4.331
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195
0 500 10001 0 502 0 0 0
380
530
480
580
430
630
680
Distance (m)
Altitude (m)
Manastirski potok stream
Figure 4: Paleo-earthflows on the right side of the valley of the Jovačka River (1971 situation), where the 1977 landslide was later formed.
Figure 5: Longitudinal profile of the stream Manastirski Potok.
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
196
Through the palaeogeographic evolution of the area during the Tertiary, it is possible to identify some
of the lithological predispositions for the formation of the Jovac landslide. As mentioned above, synchronous
deposition of terrigenous and volcanoclastic sediments took place during the Middle Miocene (Jovanović
and Novković 1988). This sedimentary-volcanogenic unit represented by clays, sands, pebbles, volcanic
ash, lapilli, tuff, volcanic agglomerates and volcanic blocks subsequently becomes an ideal environment
for the formation of the Jovac landslide. Lithologically, the southwestern hinterland of the landslide con-
sists of dacites (the Gradište and Ostrovica peaks) (Vukanović et al. 1970), while pyroclastites such as volcanic
breccias and agglomerates, as well as tuff sandstones and tuffs (Kremen Ridge) are located to the east and
southeast (Babović et al. 1977). The contact of these lithological units with the sedimentary-volcanogenic
unit determined the boundaries of the subsequent Jovac landslide.
The hydrogeological characteristics of pyroclastites, which topographically gravitate towards the land-
slide, are different than those of the dacites. Their permeability is extremely low and the regolith is rather
thin. Considering the morpho-hydrological criteria, there are two significant topographic units. The first
is the surface catchment area of the Jovac landslide and the second is the endorheic area within it. The
landslide catchment area includes not only the landslide body and hinterland of the scar, but also the lat-
eral areas that morphologically gravitate towards the main landslide body (Figure 6).
Regarding the hydrogeological characteristics of the lithological units, two zones can be distinguished:
feeding zone and collection zone. The feeding zone is the landslide body (Miocene sedimentary-volcanogenic
4722000 4721000 4720000
580000
581000 582000 583000
Built–up area
Jovac settlement
Ostrovica settlement
Landslide watershed
Endorheic area
Water supply route
Alluvium
Marls and shales
Dacites
Sedimentary–volcanogenic unit
Pyroclastites
Future landslide outline
Legend
Scale: 1:27.000
Content by: Marko V. Milošević
Map by: Marko V. Milošević
Source: Topografska karta 1:25000 Vojnogeografski
institut,  OGK Vranje, Trgovište
© 2021, Geographical Institute »Jovan Cvijić« SASA
 
 
  
  
 
 
 
 
250 0 250 500 750
m
Jovačka reka River
Manastirski potok
stream
Figure 6: Predispositions for the development of the Jovac landslide.
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unit), which has the role of hydrocollector (reservoir) and is fed by infiltration of atmospheric and surface
water. Water flowed from the impermeable areas of the dacites and pyroclastites towards the landslide body.
This was an additional factor in increasing the amount of water received by the topographic surface. The
total catchment area of the Jovac landslide was 3.06 km
2
, of which 52% was the area of landslide itself.
Another morpho-hydrographic feature is the occurrence of endorheic areas, which were detected on
48% of the catchment area (Table 4). This means that the water of 1.47 km
2
did not drain superficially but
infiltrated into the ground. The endorheic areas were divided into two areas. The first (1.07 km
2
; of which
0.519 km
2
on the landslide) included the upper part of the slope, immediately below the Ostrovica peak,
while another of 0.4 km
2
(of which 0.107 km
2
on the landslide) included the area around a palaeolake, to
the northwest from the Manastirski Potok Gorge.
Table 4: Hydrographic characteristics of the catchment area.
Hydrography Catchment area Jovac landslide
km
2
% km
2
%
Exorheic 1.59 52 0.96 60
Endorheic 1.47 48 0.62 40
SUM 2.84 100 1.58 100
In the case of the Jovac landslide, human impact is associated with the increase of the slope catchment
area. In other words, the total amount of water that a given area receives comes not only from its topographic
catchment, but also from other catchments. The inhabitants of the village of Ostrovica built a water-sup-
ply system that directed the water from below the Oštra Čuka (1040 m) (Figure 6). Despite the fact that this
area is not morphologically directed to the future landslide body, the human activity additionally increased
the water balance of the slope. The water supply system was of gravitational and flow-through type, which
resulted in water consumption exceeding the actual needs of the population (Lazarević 2000). This was
certainly not the main, but only an additional factor in triggering the landslide. The main anthropogenic
factor was the permanent humidification of the ground in the built area zone, due to the water supply sys-
tem which transferred the water from the neighboring catchment, area thus increasing the water input.
4.3 Morphometric characteristics of the Jovac landslide
The landslide boundary was determined based on the spatial distribution of elevations of the topograph-
ic surface, as explained in the Chapter 3. The topographic surface with no or with minimal differences
was declared as the landslide boundary. Thus, a polygon similar to the one defined by Petrović and Stanković
(1981) was formed. The boundaries outline the elongated area with an area of 1.58 × 10
6
m
2
. The maxi-
mum length of the landslide is 3,000m, while the widthe varies from 490m to 670m. Two distinct continuous
areas are visible, representing the values of the elevation change differences. The smaller area (0.62 × 10
6
m
2
)
is located in the highest part of the landslide. It is characterised by the lowering of the previous topographic
surface in the interval from –1 to –45m. In the middle and hypsometrically lowest part of the slope (0.96×10
6
m
2
)
(Figure 8A), the changes indicate the increased elevation of the topographic surface. The values are in the
interval from +1 to +51 m. The boundary between these two areas is a narrow belt where the elevation
change was not detected or is negligible (Figure 7).
In the area of lowering of the previous topographic surface, the differences are positioned concentri-
cally, and increase towards the interior. In the central part the highest extent of the topographic surface
lowering was –45 m. The distribution of the differences in elevation is very uneven. The greatest change
is recorded at the former gorge of the Manastirski Potok Stream. The values of topographic elevations increase
fall in the interval from +31 to +51 m. Outside this zone, the accumulation reaches +30 m only in some
places. Other values of topographic increase are distributed in various locations.
By analysing the topographic elevation difference for each DTM cell (30 × 30 m), the volume of land-
slide was determined. The estimated volume of the depleted ground, where the surface was lowered is
12.45×10
6
m
3
. The volume of colluvium in the zone of topographic surface elevation increase is 11.6×10
6
m
3
,
which is 4% less than the volume of depleted ground (Figure 8B).
Acta geographica Slovenica, 61-2, 2021
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As a result of large denivelation of the topographic surface on the landslide body, several small lake
basins have formed. They are permanently filled with water. Of the six lakes, five are located on the land-
slide body – two in the depletion zone and three in the accumulation zone (Figure 7). The sixth and largest
lake is the Jovac Lake, formed by the landslide dam of the Jovačka Reka River.
Table 5: Extreme and average morphometric characteristics of pre-sliding and post-sliding topographic surfaces.
Elevation (m) Slope (°) Curvature Aspect (°)
Pre-sliding Min 380 0.0 –5.046
Max 807 87.0 5.046
Average 568 11.0 0.015 110
Post-sliding Min 390 0.0 –0.342
Max 793 43.0 0.361
Average 567 9.6 0.014 101
Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
198
4722000 4721000 4720000
581000 582000
Landslide boundary
Contours at 20 m 
Lake outline
Elevation di!erences (m)
–45
–44.9 – – 35
–34.9 – –25.0
–24.9 – –15.0 
–14.9 – –0.1
–0.09 – 0.09
0.1 – 4.9
5.0 – 14.9
15.0 – 29.9
30.0 – 39.9
40.0 – 49.9
50.0 – 50.9
Legend
Scale: 1:21.000
Content by: Marko V. Milošević, Dragoljub Štrbac
Map by: Marko V. Milošević
Source: Topografska karta 1:25 000
Vojnogeografski institut, SRTM
© 2021, Geographical Institute
»Jovan Cvijić« SASA 
 
 
 
02 5 05 0 07 5 0 
m
4721000 4721 4720000 000 000 000 000 000 000 000 000 4720
582000 5820
Landslide boundary
Contours at 20 m 
Lake outline
Elevation di!erences (m)
–45
–44.9 – – 35
–34.9 – –25.0
–24.9 – –15.0 
–14.9 – –0.1
–0.09 – 0.09
0.1 – 4.9
5.0 – 14.9
15.0 – 29.9
30.0 – 39.9
40.0 – 49.9
50.0 – 50.9
Legend
Scale: 1:21.000
Content by: Marko V. Milošević, Dragoljub Štrbac
Map by: Marko V. Milošević
Source: Topografska karta 1:25 000
Vojnogeografski institut, SRTM
© 2021, Geographical Institute
0 250 500 750 
m
Figure 7: Elevation differences of the topographic surface of the Jovac landslide (contours refer to the present topographical surface).
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199
Area (m )
2 a)
Elevation difference (m)
–46 –23 27
54
0
0
30.000
40.000
10.000
20.000
50.000
60.000
70.000
80.000
Erosion Deposition
39%
61%
Volume (m )
3 b)
Elevation difference (m)
–46 –23 27
54
0
–400.000
–200.000
0
–800.000
–600.000
200.000
400.000
600.000
800.000
1,000.000
Erosion Deposition
52%
48%
Figure 8: Distribution of elevation differences on the topographic surface (A) and distribution of volumes (B).
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
200
Figure 9: Morphometric characteristics before and after the sliding process.
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Elevation before
0–350
350–400
400–450
450–500
500–550
550–600
600–650
650–700
700–750
750–800
Legend
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Slope before
0–1
1–3
3–5
5–8
8–12
12–16
16–18
20–30
30–40
40<
Legend
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Aspect before
No aspect
N
NE
E
SE
S
SW
W
NW
Legend
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Elevation a!er
0–350
350–400
400–450
450–500
500–550
550–600
600–650
650–700
700–750
750–800
Legend
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Slope a!er
0–1
1–3
3–5
5–8
8–12
12–16
16–20
20–30
30–40
40<
Legend
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Aspect a!er
No aspect
N
NE
E
SE
S
SW
W
NW
Legend
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Curvatur before
–0.0127 – –0.0001
–0.00009 – 0.00009
Legend
0.0001 – 0.0746
0.0747 – 0.1620
0.1621 – 0.2494
0.2495 – 0.3369
4719000
4720000
4721000
4722000
581000 582000 5830
Landslide boundary
Curvature a!er
–0.0036 – –0.0001
–0.00009 – 0.00009
Legend
0.0001 – 0.0621
0.1281 – 0.1939
0.1940 – 0.2599
0.0622 – 0.1280
Scale: 1:65.000
Content by: Marko V.  Milošević, 
Dragoljub Štrbac
Map by: Marko V.  Milošević,
Source: Topografska karta 1:25 000
Vojnogeografski institut
© 2021, Geographical Institute
»Jovan Cvijić« SASA
 
 
 
 
02 5 05 0 07 5 0 
m
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5 Discussion
Although the descriptions of Jovac the mechanisms of movement of the Jovac landslide by Lazarević (1977)
and Petrović and Stanković (1981) fit into the category of »flow«, the authors explicitly referred to the move-
ment as sliding. The analysis of the planar form of the Jovac landslide, where the length is much greater
than the width, according to the nomenclature of Varnes, modified by Hungr et al. (2014) and the inter-
national classification of landslides according to the movement mechanism IAEG (1991–1992), indicate
that the flow-associated elements are also present.
This statement can be analysed by three indicators based on the analysis of two DTMs, and related to
the elevation differences of the situations before and after the slide.
The first indicator is runoff. It shows how many cells (30 × 30 m pixels) gravitate to an observed cell,
i.e. how large is the »catchment area« of each cell. For this analysis, only the values obtained from the pre-
sliding DTM were considered. The second indicator is the elevation difference of two DTMs for each selected
cell (negative or positive, indicating depletion or accumulation). The third indicator is the current eleva-
tion of a cell, the elevation after the sliding process.
Comparative analysis of these indicators was a valuable tool in geomorphological reconstruction of
the area. The cross-section in the depletion zone (with lowering of the topographic surface) showed that
the depletion peaks do not follow the peaks of the runoff capacity. The runoff peaks are directly propor-
tional to the drainage lines. This indicates that the sliding process in the upper part of the landslide was
independent of the morphology of the topographical surface (profile B–Bo in the Figure 10A). The deple-
tion zone almost completely overlaps with the endorheic area and conditions for water saturation of soil
and rock are favourable (Lollino, Giordan and Allasia 2014).
The cross sections in the accumulation zone show a clearly different situation. Profile C–Co shows
a matching of the runoff peaks, but not so many conspicuous peaks in the increase of the topographic val-
ues (Figure 10B). The same is seen on the D–Do profile, with slightly better visible peaks compared to C–Co,
thanks to its lower position on the slope (Figure 10C). This feature may indicate that the highest accu-
mulation of the material occurred along the drainage lines. In other words, the morphology of the pre-sliding
surface determined the movement of colluvial material from the depletion zone (upper slope) through
the accumulation zone (middle and lower zones).
To prove the assumption that in the lower part of the landslide the flow followed the stable palaeoto-
pographic surface, it was necessary to include the third indicator, the elevation of the cells after the slide
(Figure 11D). Figure 11D shows that the convex portions of the current topographic surface overlap with
the peaks of runoff and accumulation. A convex profile of the topographic surface in the earthflow accu-
mulation zones was also pointed by Soeters and van W esten (1996). This undoubtedly proves that the colluvial
material from the depletion zone continued to move downwards following the pre-existing morphology
of the middle and lower parts of the slope. The underlying rock was certainly stable, thanks to the pyro-
clastite zone on the northeast side. This type of movement was a consequence of supersaturation by water,
which decreased the viscosity of the colluvium and allowed it to follow the slope morphology. This also
explains the asymmetry in the colluvium thickness, which is greatest in the zone of the former gorge of
Manastirski Potok.
Based on the presented relationships between the colluvium and topographic surface we conclude that
the Jovac landslide has elements of earthflow movement. According to the ICL classification (Internet 1),
the Jovac earthflow is in the category of large landslides (≥ 10
6
m
3
). In Serbia, landslides with similar
volume and lithology usually occur along the banks of large rivers and their movement mechanisms
are rotational and planar. The right bank of the Danube River hosts the Bocke landslide, Krčedin
landslide (Mészáros 2013), Cigansko Brdo (Janjić 1996), Rujište (Lazarević 1957; Janjić 1996), Provalija
(Luković 1951), while the Umka and Duboko landslides are located on the right bank of the Sava River
(Abolmasov et al. 2014).
Figure 10: Relationship between discharge and elevation differences along cross sections (see also Figure 1).p p. 202
Figure 11: Model of the Jovac landslide adapted from Petrović and Stanković (1981) (A); longitudinal profile of the Jovac landslide (B); cross section
in the topographic decrease zone (C); cross section in the increase zone of Manastirski Potok Gorge (D) (see also Figure 1).p p. 203
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
202
Distance in pixels
Number of pixels
m
0
30 –30
40
–20
70
10
10
–50
20
–40
50
–10
80
60
–0
90
Pixel catchment area Elevation difference (m)
B Bo
a)
Distance in pixels
Number of pixels
m
1
1000
5
10
30
10
–5
100
0
15
20
25
Pixel catchment area Elevation difference (m)
C Co
b)
Distance in pixels
Number of pixels
m
1
1000
20
30
10
0
100
10
40
50
60
Pixel catchment area Elevation difference (m)
D Do
c)
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203
Scarp
Colluvium
Cracks
New river–bed of Jovac
m
900
700
500
300
41˚ a)
125 250 375 500
m
Colluvium
Vo l c a n o–sedimentary unit
(clays, sands, volcanic ash, lapilli)
Pyroclstites (volcanic breccia,
agglomerates, tuffite sandstones
and tuff)
0 625
143˚
D
550
525
500
475
450
Manastirski Potok
Gorge
d)
D
0
m
Pre–sliding topography Post–sliding topography
500
800
750
700
B
Source area
Flank
Scarp
Paleoflank
Scarp?
c)
140˚
B
0
m
Pre–sliding topography Post–sliding topography
625 750 375 250 125 0
Main Scarp
h=35 m
Jovacka
Reka
River
50˚
Source area Main track
Depositional
area A
A
0
875
750
625
500
375
3.500
Colluvium
m
b)
Pre–sliding topography Post–sliding topography
0 3.000 2.500 2.000 1.500 1.000 500
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Marko V . Milošević, Dragoljub Štrbac, Jelena Ćalić, Milan Radovanović, Detection of earthflow dynamics using …
6 Conclusion
According to the systematization of Varnes (1978) and Cruden and Varnes (1996), the mechanism of the
Jovac landslide colluvium movement can be determined as flowing. In terms of material (criteria of Varnes
1978), it belongs to the category of earth, containing high proportion of particles about 2 mm in size. Using
the modified Varnes (1978) classification of landslides (Hungr, Leroueil and Picarelli 2014), the Jovac land-
slide belongs to the category of earthflow. Its estimated volume is 11.6×10
6
m
3
, which is a significant difference
compared to the earlier estimates of 150 × 10
6
m
3
(Lazarević 1977; Petrović and Stanković 1981). The rea-
son for such a difference lies is that the earlier researchers had rather poor spatial data, mostly collected
by fieldwork observations. We believe that the exceptional size of the landslide and the degree of damage
may have influenced the earlier researchers to somewhat subjective conclusions.
In determining the landslide contour, two DTMs were used, one with the situation before the land-
slide and one with the situation after the landslide. In order to explain that the elevation differences between
them are the consequences of the sliding process, it was necessary to define the procedure to avoid tech-
nical errors. Possible errors could be related to the incorrect overlapping of two DTMs and to the possible
presence of systematic errors due to different types of elevation data acquisition. After completing the test-
ing, we obtained the exact elevation differences between two DTMs caused by the sliding process.
The use of small- and medium-resolution DTMs, in this case 30 × 30 m (Corsini et al. 2009; Hu et al.
2019), can be a relevant data source for landslide studies, provided that the dimensions of the landslide
are large enough to be visible in a DTM. The DTM resolution used makes the study comparable world-
wide, as both EU and global DTMs use this resolution. In the case of the Jovac landslide, the pre-slide data
were obtained from the topographic map 1 : 25,000. The input data determined the resolution of 30 × 30 m.
Judging by the area of the Jovac earthflow (1.58 km
2
) and the volume (11.6 × 10
6
m
3
), we conclude that the
DTM at this resolution contains the information relevant to the earthflow formation process. We also con-
clude that the analysis of the elevation differences of the topographic surface before and after the landslide
is an appropriate method to study earthflows (Fernández et al. 2011; Giordan et al. 2013). The endorhe-
ic character of the paleotopographic surface, determined by the previous earthflow process, was one of
the conditions that strongly contributed to the reactivation of the Jovac earthflow in 1977.
ACKNOWLEDGMENTS: The authors would like to sincerely thank an anonymous reviewer for his valu-
able comments on the manuscript, which demonstrate the very responsible way in which the review process
was handled.
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