Reconstruction of landslide movements using Digital Elevation Model and Electrical Resistivity Tomography analysis in the Polish Outer Carpathians

Highlights

• Multidisciplinary approach for complex landslide study.

• Geomorphologic and DEM analyses reveals western and eastern part of landslide.

• ERT analysis show internal structure of eastern part of landslide.

• Variable colluvium activity within the landslide.

• New insight in the stages of landslide development using multidisciplinary approach.

Abstract

Landslides are a major threat to the environment, infrastructure and human activities, especially in mountainous and hilly areas. It is therefore important to accurately identify the mass movements triggering these mechanisms. This paper presents the impacts of lithotectonic conditions on the formation of mass movements on the example of the landslide that is located in the northern part of the Polish Outer Carpathians. In the area of the research, the ratio of the total area of landslides to the surface of the area reaches even 20%. The interpretation of a high resolution Digital Elevation Model (DEM), Electrical Resistivity Tomography (ERT) and fieldwork results allowed for the reconstruction of the landslide movements and dividing them into two areas; the western one, dominated by rotational movement, and the eastern one, featuring rotational and translational movement. It was found that the eastern part is more active now as it probably was also in the past, which might have resulted from the lithotectonic conditioned or from the impact of the flowing waters of the Dunajec River. Moreover, in the eastern part of the landslides, a small-sized ridge (55 m × 25 m) was identified, which shows greater stability in comparison with the colluvium that surrounds it. In order to explain the lower rate of movement of this landform, a morphometric analysis and research using ERT were performed. The geophysical measurements showed that the ridge comprised rock formations of greater resistivity than its surroundings. It is most likely that the only preserved sandstone packet, constituting the original secondary escarpment, became separated from the bedrock due to rotational movement. The presented studies indicate that the landslide was created due to geological and atmospheric conditions. A clear revival of landslide movements took place after significant precipitation events that last occurred in the years 2010 and 2015. The bedrock substrate due to its lithology and tectonics, facilitates these movements. It was found that the landslide studied is a complex entity, characteristic of the Polish Outer Carpathians, that has undergone multiple stages of development. The landslide is active or periodically active and, therefore, must be excluded from the planned development as well as from other forms of human activity.

Introduction

The creation and development of surface mass movements are related to the environmental conditions of the site. First of all, they are mainly related to the local geological structure, both in terms of the lithology of the underlying strata as well as their tectonic and hydrological conditions and the slope inclination. Depending on the kind of geologic formations found in the underlying strata, slope angles and hydrological conditions, shallow slides may occur within the weathered bedrock layers, or deep-seated landslides may occur, disrupting the structures of an underlying rock layer or the bedrock (Bober et al., 1997, Margielewski, 1998, Margielewski and Urban, 2017, Mrozek et al., 2000). In addition, the rates of the movement of colluvium may vary. Additionally, fragments or packets of the colluvium may move with different velocities, thus experiencing shifts with respect to one another (Travelletti and Malet, 2012, Travelletti et al., 2012, Prokešová et al., 2014, Boon et al., 2015, Ausilio and Zimmaro, 2017, Di Maio et al., 2020). Changes in the slope morphology and ecosystem lead to changes in the substrate hydrology, groundwater circulation and humidity distribution (Alexandrowicz and Margielewski, 2010, Stoffel et al., 2014, Gance et al., 2016, Neto et al., 2017, Pisano et al., 2017, Crawford and Bryson, 2018, Sandholz et al., 2018). A number of geomorphological and hydrogeological processes inducing surface mass movements with catastrophic consequences are initiated by atmospheric precipitation, both long-lasting (pourable) and volatile (rapid), as well as by rapid melting of large masses of snow in the spring. An increased amount of rainwater in a given area intensifies the flow in the watercourses, which in turn can undercut the slopes through lateral erosion. The hydration of the soil on the slopes weakens their cohesion and causes an additional load. In addition surface mass movements are affected by anthropogenic factors, primarily by the manner and intensity of land use (Lissak et al., 2014, Ling et al., 2016). The greatest risk of landslides arises when several factors occur simultaneously. Landslides, due to significant material damage that they cause, represent a serious geo-hazard, which must be realistically taken into account in spatial planning (Wieczorek, 2015, Cichy, 2015, Mateos, 2017, Ashournejad et al., 2019). Landslides bring losses and functional and structural damage every year, such as the degradation of the terrain and structures placed on it (residential buildings, road network, sewage system, telecommunication lines, electricity, agricultural crops, and forests). They are also an extremely troublesome, sometimes even fatal, phenomenon for people (Crozier, 1986, Dearman, 1991, Djuric et al., 2015, Highland and Geertsema, 2019).

In Poland, landslides are located mainly in the south of the country in the area of the Polish Outer Carpathians (Poprawa and Rączkowski, 2003, SOPO data, 2018), as it is the outermost part of the Carpathian orogeny (Książkiewicz, 1977). Their number estimated, based on the Landslide Counteracting System project, can be as much over 50–60 thousand (SOPO data, 2018). These areas, with the exception of the Low Beskids and the Bieszczady Mountains, are densely populated, which generates significant material losses due to the activation of old and new landslides. The increase in the activity of landslide movements in recent years, their surface range and problematic predictability of their activation has caused considerable interest among local governments and geologists as well as scientists. The aim of their work is to reduce the losses and damage caused by destructive landslide processes by determining the landslides triggers (Peruccacci et al., 2017, Šilhán et al., 2019).

Therefore, it is important to recognize the internal structure of landslides and the mechanisms of mass movements (Carey et al., 2015, Chalupa et al., 2018). The reconstruction of the chronology and the development of mass movements and identifying the reasons for their formation can serve as a basis for modeling future landslide events and their re-activation (Corominas and Moya, 1999, Vallet et al., 2016, Malik et al., 2017, Migoń et al., 2017, Peng et al., 2018, Coltorti and Tognaccini, 2019).

Research into the ways of monitoring mass movements and the identification of their causes belong to the most important issues waiting for a quick solution. This requires a multidisciplinary research approach based on many methods. The geologic conditions that influence different activity rates of the colluvium may be determined by means of geotechnical investigations such as boring and probing. These methods enable gaining information on the lithology, geotechnical parameters, and hydrogeological conditions of the colluvium and the underlying rock layers. Nevertheless, such investigations supply only one-dimensional information, although they require performing a large number of measurements (Sato et al., 2007). Thus, other methods, notably geophysical methods, prove to be helpful in this matter. They allow performing an identification of the substratum ground in a continuous manner and are relatively inexpensive (Jongmans and Garambois, 2007, Perrone et al., 2014, Whiteley et al., 2019).

The use of geophysical methods in the detection of the internal structure of landslides has increased with the introduction of automation into geophysical equipment, digital recording of data, and perfecting of the procedures of the processing and interpretation (Loke and Barker, 1996, Farquharson and Oldenburg, 1998, Loke and Dahlin, 2002, Lebourg et al., 2005).

Electrical Resistivity Tomography (ERT) is the most frequently used and very effective method in this type of research (Perrone et al., 2014, Pánek et al., 2014, Pasierb, 2015, Uhlemann et al., 2016, Wilkinson et al., 2016, Tábořík et al., 2017, Bellanova et al., 2018; Pasierb et al., 2019). Results obtained using this method allow determining the lithological sequences, reconstructing the lateral extension and thickness of the colluvium, determining the internal structure of landslides, potential slip planes, specifying the sliding surfaces between the slide material and the underlying bedrock, evaluating the groundwater conditions for estimating the dynamic behavior of landslides, monitoring the water infiltration in the colluvium and movement characterization (Krejčı́ et al., 2002, Lapenna et al., 2005, Jongmans and Garambois, 2007, Colangelo et al., 2008, Perrone et al., 2008, de Bari et al., 2011, Travelletti et al., 2012, Gance et al., 2016, Břežný et al., 2018, Crawford and Bryson, 2018, Szczygieł et al., 2019).

Geodetic measurements, either land-based or performed from the air or a satellite, also play an important role in landslide research, especially in the measurement of the rates of colluvial movement (Refice et al., 2000, Borkowski et al., 2011, Travelletti et al., 2012, Cebulski, 2014). The ever more popular Light Detection and Ranging (LiDAR) technology allows to generate high resolution Digital Elevation Models (DEMs), which are used in studying geomorphologic processes including landslides (Oppikofer et al., 2009, Travelletti and Malet, 2012; Saleem et al., 2019).

An analysis of the obtained DEMs with the use of GIS software enables determining landslides boundaries accurately, finding their morphometric parameters, and also describing the land cover (Fidelus-Orzechowska et al., 2018). Generating hillshade and slope maps allows analyzing the surface of landslides and identifying colluvial packets, characterized by different degrees of activity, within these landslides.

The aim of the research was to present the importance of lithotectonic conditionality in the formation of mass movements, based on the Digital Elevation Model, Electrical Resistivity Tomography and geomorphological studies. The analysis was presented on the example of the Tubendza II landslide, which is located in the northern part of the Polish Outer Carpathians and with respect to other landslides presented in the literature. In the area of research, the landslides surface rate (the ratio of the total area of landslides in the area, to the surface of the area) reaches even 23% (Wieczorek and Kułak, 2015).

The Tubendza II landslide is a landslide with a non-uniform structure characterized by different rates of colluvial movement in its different parts. This landslide was selected for study purposes because of the different types of slides present within its landform. A small ridge that was also noticed in the eastern part of the landslide was more stable in comparison with the surrounding colluvium. The variability of the movement of the colluvium may result from differences in the geologic structure. The main objective of the study was to recognize the mechanism and genesis of the mass movements in order to reconstruct the landslide movements as well as to explain the reason for the different rates of the colluvial movement.