Keywords

A Short History

The international literature on mass movements is rich in landslide classification, given by the wide range of processes, forms, or displaced material. Mass movement classifications are given by Sharpe (1938), Hutchinson (1988), Zaruba and Mencl (1969), McCalpin (1984), Cruden and Varnes (1996), Dikau et al. (1996), Cruden and Fell (1997), Lee and Jones, (2004) or Hungr et al. (2013), but the most used classification is the one given by DJ Varnes in 1978 and later on, in 1984.

The wide range of processes, forms, and potential consequences is well reflected in the extended Romanian geomorphologic literature, focusing on both fundamental and applied considerations regarding slope mass movements. Several milestones can be set up along the last 100 years of researches. The following selective analysis emphasizes different patterns within the research, conditioned by the fundamental knowledge requirements, end-user demands or access to measurement tools and new, updated research methods, as detailed in the brief attempt below.

1910–1960: Pioneering and Fundaments

From its early beginnings, the Romanian literature follows and sometimes even anticipates, the international framework, while the litho-structural environment extremely prone to landslides allows the very first studies to be traced back towards the early twentieth century. The geomorphologic literature of the 2–5th decades of the twentieth century was strongly marked by geologic studies focused especially on the mass movements’ classifications (e.g., Mrazec 1923; Munteanu-Murgoci 1923; Macovei and Botez 1923; Mihăilescu 1939; Dragoş 1957).

The first studies dealing with landslides as active morphodynamic processes, coupling slope and channel environments, date back in the 1920s and belong to Macovei and Botez (a study realized in 1915, but published due to the conditions imposed by the First World War only in 1923), Mrazec (1923) or Munteanu-Murgoci (1923). A very interesting overview on the variety of forms and processes offered by the Curvature Subcarpathians of Romania is given in March 1915 by Macovei and Botez, which studied the numerous falls and slides that occurred during the first trimester of that year. They differentiate (maybe for the first time in the Romanian literature) several types of processes and associated forms: slides stricto-sensu (affecting areas up to 140 ha and occurring …only when the topographic slope is according to the strata inclination…), flows (completely different process, described as developing along three main morphodynamic sectors—the torrential origin area, the flowing track and the terminal accumulative fan—which involves a fluid displacement of oversaturated, fine material, looking more like a glacier in terms of morphology), debris slides (affecting anaclinal strata), and falls (associated mainly with river undercut). Besides giving a brief description of the causes of such processes, the article outlines the importance of serious land reclamation works among which are transversal torrential dams and reforestations (with a role in diminishing the process, not stopping it completely).

A more detailed geomorphologic description is given by Mihăilescu in 1939, who, in its Geomorphology Course given at the Faculty of Sciences in Bucharest makes a correlation with the Italian term frana (which is even used by the author in 1927 as neologism), citing the work of Almagia (1910). He suggests the term, relatively translated as displacement (in Romanian pornitură) and divides the process in two main categories: dry displacements (falls, topples) and wet displacements (slides, flows). The author emphasizes the morphology and morphometry of such processes (as seen in Fig. 11.1a), which may affect entire mountains (Fig. 11.1b). Later on, in 1939, the same author uses the morphogenetic criterion (initial stage of the material, displacement mechanism, resulted form) in order to classify the slope mass movements into topples and rolling (Fig. 11.2a), humid and wet slides (Fig. 11.2b), dry and wet falls (Fig. 11.2c, d).

Fig. 11.1
figure 1

The morphology of pornituri (slope displacements) according to Mihăilescu (1927): frana “typical” slide (a), displacement sketch across a mountain (b)

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Fig. 11.2
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The classification of Mihăilescu (1939): falls and rollings (a), humid mound-like slide (b), endo-karst dry falls (c), coastal wet falls (d)

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Later on, in 1946, he classifies them only into dry (topples and compaction) and humid (solifluxion, earth flows, debris torrents and slides) displacements. In 1957, Dragoş divides them according to the environment into subaerial—falls, flowing sands, strata bending, solifluxion, slides—submarine and tectonic) (Dragoş 1957). Towards the end of this time period appear the first attempts to provide national distributions of landslides. In 1959, Rădulescu was claiming that “…the landslide studies in Romania have been done in a way which is not well systematized…therefore, even though we have well-fundamented papers, synthesis works cannot be realized yet…” (Rădulescu 1959a, b). The author provides a map with the distribution of different landslide types (slides, flows, and falls) and even gives a rough estimation (at a national scale) of 116,000–900,000 ha affected by these processes.

By looking at the above-mentioned contributions, we may notice that the morphologic and morphodynamic criteria which were used by these landslide-geomorphology pioneers get their classifications extremely close to the ones used worldwide at that moment (Almagia 1910; Sharpe 1938), even anticipating those given by Hutchinson (1988) or Zaruba and Mencl (1969).

1960–1990: Forms, Processes, and Remediation Suggestions

During the following three decades, the landslide systematic studies went in parallel, in two main directions: a fundamental research one (in the attempt of offering explanations in terms of forms and processes and their predisposing and preparing/triggering factors) and a newly-born but fast growing applied approach (enhanced by the economical framework, which was focusing on finding the optimal land-use strategies or enhancing land reclamations (Morariu and Tufescu 1964; Ichim and Lupaşcu 1975).

The interest was oriented towards mass movement morphodynamics (e.g., Cioacă 1967; Ielenicz 1970; Ichim 1972; Posea 1972; Surdeanu 1975; Bălteanu 1970; Grecu 1982), litho-structural predisposition (e.g., Donisă 1968; Badea 1972; Grecu 1983; Ichim 1972; Ielenicz 1984), age (Morariu et al. 1964) regional patterns of their morphology (e.g., Băcăuanu 1977; Ielenicz 1981; Bălteanu 1983; Grecu 1985), typological mapping (Grigore and Ielenicz 1972; General Geomorphological Map of Romania 1:200,000, Institute of Geography, Romanian Academy) and towards the major interactions between slope and channel processes (e.g., Dragomirescu and Gâştescu 1960; Posea 1969; Popescu and Popescu 1978; Bălteanu 1974; Surdeanu 1975). All throughout the period, the shy and not that numerous translations to/from English introduced into the Romanian geomorphologic language, a mistake that was carried out up to recent times by many authors: the term landslides was associated to the Romanian correspondent of alunecări, which actually correspond only to the subtype of slides.

These decades are rich in systematic studies, among which the most important might be those of: Martiniuc and Băcăuanu (1961; the authors adapt a landslide classification to the structural conditioning of the Moldavian Plateau, a typical homocline area—Fig. 11.3); Tufescu (1964; according to the causes, he separates between mechanical: topples, falls, piping, strata bending, compaction, creep, and water-driven: flowing sands, earth flows, solifluxion, slides; Fig. 11.4); Coteţ (1969; according to the water content, he separates among dry—falls, rollings, compaction, humid—slides, solifluxions, and mixed—combination between gravitational and erosional processes—displacements); Bălteanu and Mateescu (1975; are providing a first unitary, national-scale map of present-day  modeling processes); Bally and Stănescu (1977; provides a geological—both lithologic and structural—insight and finds inspiration in the classifications of Sharpe and Hutchinson).

Fig. 11.3
figure 3

The classification of slides according to Martiniuc and Băcăuanu (1961): mixed-fragmentation slides (a), monticule-like slide, step-like slide (c), wave-like slide (d)

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Fig. 11.4
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The classification of slides, according to Tufescu (1964): furrow-like slides (a), monticule-like slide (b), pseudo-terraces like slide (c), entirely landslide-affected slope (d)

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Among the landslide types, the deep-seated ones (considered by all authors as displacing more than 10 m thick deposits) raise a particular interest, due to the high morphogenetic complexity and large magnitude. There are numerous studies aiming at establishing the causes of such processes, mainly in the neotectonically active area of the Curvature Carpathians (for which area, Posea and Ielenicz (1970, 1976) and Posea (1972) are using terms like massive zonal slope slide, profound massive slope slide, profound massive valley slide, or landslide valleys; Posea and Popescu 1976; Bălteanu 1970, 1971), the Eastern Carpathians (Sârcu 1962; Surdeanu 1975, 1976; Surdeanu and Rădoane 1976) or the Transylvanian Depression, where a particular type of landslides, called in Romanian glimee, finding its most representative morpho-litho-structural occurrence environment, tried to made its way in the nomenclature (suggested as a landslide type during the 1964 XIth International Geographical Congress). Studied by Morariu and Gârbacea (1968) and later on by Josan and Grecu (1981), Grecu (1982, 1983, 1985), Gîrbacea and Grecu (1983) and Gârbacea ( 1992, 1997, 2013) these old (even Wurm), large (Şaeş complex extending across 1500 ha), deep-seated (frequently affecting the regolith and the bedrock together) particular processes barely find a correspondent in international classifications. While their genesis is still largely debated, their morphology gets them sometimes close to lateral spreads and sometimes can only include them inside the very general complex type.

Other interesting classifications are given by Mamulea (1975; mass movements without an own displacement subsurface, mass movements with an undetermined displacement subsurface, mass movements with a determined displacement subsurface), Băcăuanu (1977; classifies the landslides according to the homocline landforms of the Moldavian Plateau), Ielenicz (1970; gives a national-scale evaluation of landslide distribution and outlines the common morphological traits according to the main morphostructural units) and Bălteanu (1983; adapts for the Curvature Subcarpathians the classification of Varnes 1978). A particular interest is raised by mudflows, acknowledged as showing a high frequency but low-magnitude dynamic pattern (Tufescu 1964; Bălteanu 1976, 1983).

1990–2000: New Horizons

After 1990, the interest towards landslide classification diminished and such approaches could be found in wide synthesis works, which outline the large number of criteria used for such purposes: the relationship between the sliding surface and the geological structure, evolutive direction, type of movement, thickness, shape, etc. (Josan et al. 1996; Posea 2002). Instead of systemic studies, over the last two decades of the twentieth century there was a growing concern for applied studies, focusing on landslides as land degradation processes (e.g., Surdeanu 1998; Sandu 1998), the dynamics of conditioning factors (e.g., Bălteanu and Cioacă 1997; Cioacă 1996; Dinu 1997; Posea and Vespremeanu 1985; Surdeanu 1992) or on the triggering factors and their spatial and temporal patterns (e.g., Dinu and Cioacă 1997; Cioacă and Dinu 1998). The technological (computers, software) and methodological (the interdisciplinary character of applied statistics or remote sensing imagery) developments, together with the highly increasing opening towards new, easily accessible state-of-the-art information, marked the geomorphological literature in terms of both quantity and quality.

Since the end of the twentieth century, the interest was shifted steadily towards the analysis of slope mass movements as hazards and subsequently induced risks, as these processes were started to be related through evolutive models with the potential consequences that they might inflict (e.g., Surdeanu 1985; Bălteanu 1992; Rădoane et al. 1995; Bălteanu et al. 1989, 1996; Grecu 1992; Loghin and Păunescu 2002; Armaş et al. 2003, Surdeanu et al. 2010). A detailed review of modern approaches concerning landslide susceptibility, hazard or risk, at either local, regional or national scales using both qualitative and quantitative methods is given by Bălteanu et al. 2012 and by Micu et al. Chap. 32, this volume.

Landslide Typology in Romania: An Updated Picture

For terminology-harmonization reasons, in this chapter the most widely used classification available in the specialist literature, i.e. the one of Cruden and Varnes (1996, improved by Hungr et al. 2013) was used, in order to outline the most widespread landslide types in Romania.

Slides

In Romania, the large slide typology reflects the wide complexity of predisposing, preparing, and triggering factors. The Carpathian Mountains, Subcarpathian Hills and Depressions, Transylvanian or Moldavian Plateaus show extremely prone settings for slide occurrence, being in the mean time among the country’s regions featuring a high concentration of elements at risk.

The mountainous flysch sector is characterized by the existence of large, dormant (partially relict) slides (rock slides, debris slides, or complex) (Fig. 11.5a). Showing a low-frequency high-magnitude pattern, these slide types present a lot of sectors with recent reactivations, either at their toe or scarp. The hilly or tableland areas developed on molasse deposits are featuring very frequent but low-magnitude slides, in form of earth slides and flows, rock slides and rarely debris slides (Fig. 11.5b). In these areas, the slides are forming large complex areas in which they associate with (either as conditioning or being induced by) erosion processes, especially in the form of rill and inter-rill erosion and rarely gullies.

Fig. 11.5
figure 5

Deep-seated rock slide in the Buzău Carpathians (Şeţu, a) and shallow translational earth slides in the Buzău Subcarpathians (Bălăneasa catchment; b) (Photos M. Micu)

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There are two main triggers of the wide variety of slides, either in form of single or multiple slide events: precipitation and earthquakes. Torrential rainfalls during summer are causing earth flow pulsations that are enhancing slope instability in the main sources’ area in the form of retrogressive slides. The spring showers (overlapping snowmelt in the mountains or high hills) and autumn rainfalls are frequently causing deep-seated earth or rock slides in the flysch Carpathians, as well as a wide spectrum of shallow slides in the Subcarpathians or plateaus. Even though not fully explicitly outlined, the earthquakes are determining both co-seismic and post-seismic failures such as rock slides combined with rockfalls or debris flows (e.g., Bălteanu 1979; Mândrescu 1981, 1982; Radu and Spânoche 1977; Micu et al. 2015). Due to the long-lasting habitation, the hilly areas of the Subcarpathians were marked by an intense human impact on the environment. The large deforestations throughout the second half of the nineteenth century, the large development of communication networks along the second half of the twentieth century or the changes occurred in land ownership after the fall on the communist regime (1990 onwards), acted as preparing factors for slides occurrence and reactivation.

Flows

Fast moving and extremely dangerous from the point of view of potential damages, the flows may frequently affect the debris and soils/earth and less likely the rocks. The morphometrical variables and the litho-structural conditions of the Carpathians are making them less prone to rock or debris flows if compared to the Alps or the Pyrenees. A detailed description of their occurrence conditions and further development framework is provided in this volume by Pop et al., Chap. 14.

The very folded and faulted structure of the Subcarpathians, the loose sandy, marly or clayey formations that are forming the molasse deposits on which they are built makes this hilly region extremely prone to such processes, especially in the form of earth flows. Under specific conditions (amount of water content especially), flows can range within the same process from hyperconcentrated flows to earth flows or debris flows. Small nonchanneled and superficial earth flows, small channeled earth or debris flows or deeper earth/debris flows are preconditioned also by the thick sand or gravel unconsolidated deposits that correspond to the Upper Pliocene–Quaternary period (frequent in the Moldavian, Curvature or Getic Subcarpathians, Central Moldavian and Someş Plateaus, Western Hills). Their pulsatory behavior is imprinted by the summer torrential rainfalls. The rich content of clay minerals (illite, montmorillonite) contributes to successive overpasses of Atterberg limits and, depending on the regional and seasonal precipitation patterns, the processes can shift from a viscous to a plastic displacement, like frequently happens in the Curvature Subcarpathians (e.g., Chirleşti mudflow, described in detail by Bălteanu and Micu in 2012 (Fig. 11.6). Known in the Romanian specialized literature as “alunecări curgătoare”, this processes found a correspondence within the classification of Hungr et al. (2013) as flowslides.

Fig. 11.6
figure 6

Debris flow (Siriu; a; Photos M. Micu) and earth flow (Chirleşti; b; GeoEye aerial photo, 2013) in the Buzău Carpathians

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Falls

According to Ilinca (2010), in the Carpathians, these processes occur in the high mountain area, mainly in form of rockfalls, where the predisposition given by the presence of natural rock slopes exists. In the mean time, preparing and triggering factors for rock fall occurrence are enhanced along the roads that cross the Carpathians (Fig. 11.7), situation in which the sources might be both natural and anthropic (undercut slopes).

Fig. 11.7
figure 7

Rockfalls in the Buzău Carpathians, along National Road nr. 10 (Photos M. Micu)

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A recent estimation of rock surfaces in the Carpathians (Vasile et al. 2015), shows that the area covered by rock walls reaches about 17 km2, approximately 3 % of the total surface of the mountain range. This area is theoretically more prone to rockfalls. As described by Ilinca (2010), these events are generally reported mainly in hard jointed rock formations. The joints or discontinuities in the rocks appear due to several tectonic, stratigraphical, mechanical, climatic, and anthropogenic factors. As Hencher (1987) pointed out, a rock slope can be affected by many types of discontinuities like tectonic joints, faults, lithological boundaries, sheeting joints, bedding planes, fissures, cooling joints, and metamorphic fabrics. Along these discontinuity planes the shear strength is looser, especially where groundwater infiltration exists. The relationships between joints and slope face define the type of rock detachment which can be planar, wedge, topple, overhang, or complex (Hencher 1987; Hantz et al. 2003).

Spreads

Moving with a much slowly speed compared to the previous mass movement categories, the lateral spreads (Fig. 11.8) are characterizing the areas in which more-or-less cohesive rock formations are overlaying and slowly moving onto much finer materials, without featuring an obvious ruptural surface. Even though not that common, lateral spreads can be found in Romania along the large flood plains of rivers crossing the Eastern (flysch) Carpathians, in the low-altitude Moldavian or Transylvanian plateaus or along the Danube, at its contact with the Dobrogea Plateau. In Transylvania, a rather resembling process (at least from a morphologic point of view, since the morphogenesis should be better assessed in terms of failure mechanisms) is known in the Romanian specialist literature under the name of glimee (Fig. 11.8a; a comprehensive literature has been provided in the above text).

Fig. 11.8
figure 8

Glimee at Şaeş (Transylvanian Tableland, a; Photo M. Micu) and lateral spread at Seimeni (Dobrogea Tableland, b; GeoEye aerial photo, 2014)

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Interesting cases of such processes are encountered along the Danube, at Seimeni, Dunărea, Topalu. Due to the lithology (loess-like deposits), the high level of the underground waters, the compaction caused sometimes (like in the case of the city of Galaţi) by slope overload and the lateral erosion caused by the Danube in its seasonal level shifting leads to the slow occurrence of cracks and spreads that may affect houses, blocks of flats, or almost entire neighborhoods or villages. Such an example is the village of Seimeni, which was affected in 1999, 2005, and 2010 by such processes that endangered more then 20 households (Cazacu and Drăghici 2011).

Topples

Less widespread in comparison with the other mass movement processes, topples are affecting fissured cohesive rocks overlaying marly or clayey slipping strata. This alternation may be encountered throughout the flysch chain of the Eastern Carpathians, where the intense folding is often bringing to vertical fissured sandstone packs which may later end up on topple on top of the schistose intercalations. In this region, topples are quite often combined with falls, making them more difficult to be distinguished. Another prone environment is the one of the Pliocene formations of the outer Curvature Subcarpathians, where loess-like deposits overlaying clay lens lead to topple occurrence but with a smaller magnitude (Fig. 11.9).

Fig. 11.9
figure 9

Gravel/sand topple at Muscel (Buzău Subcarpathians; Photos M. Micu) before and after the collapse

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Creep

As either shallow (seasonal; Fig. 11.10a) or deep-seated (without depending on seasonal variability; Fig. 11.10b), the creep is a common process all throughout the Carpathians and Subcarpathians.

Fig. 11.10
figure 10

Soil creep at Valea Viei (Buzău Subcarpathians; a) and rock slope deformation (rock creep) at Cătiaşu (Buzău Carpathians; b) (Photos M. Micu)

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In the flysch sector of the Eastern Carpathians, it is quite often that the creep represents the incipient stage of large, deep-seated landslides. Rarely described in the literature (Bălteanu 1983; Băcăinţan 1983; Rădoane 1995), the creep itself barely poses threats to society, but an enhancement of its displacement speed may be associated with potential slide initiation.

Compound/Complex

The presence, especially in the Subcarpathians (very common in the Curvature sector, but encountered also in the Moldavian and Getic units), of large areas affected by compound or complex landslides (Fig. 11.11), is conditioned from a morphological or morphodynamic point of view mainly by the combination of gravitational and hydrological processes.

Fig. 11.11
figure 11

Complex landslide at Siriu (Buzău Carpathians) (Photo M. Micu)

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Gully erosion has contributed to the enhancement in landslide typology, their morphodynamic patterns, their frequency, and more often magnitude. Previous studies (Bălteanu 1983) showed for the region of the Buzău Carpathians and Subcarpathians that, if gully-affected slopes represent only 1.5 % out of the entire area, the slopes across which the gully erosion—less present, apparently playing a reduced role, but actually conditioning and enhancing slope mass movements—increases in proportion to 38 %.

Conclusions

The complexity of predisposing (litho-structural conditions, neotectonics), preparing (land-use changes as a result of human intervention on the environment), and triggering (spatial and temporal patterns in precipitation or temperature distribution, seismicity) factors that are characterizing the Romanian territory makes it prone to a wide variety of slope and channel present-day modeling processes, among which the landslides are playing a determinant role in numerous physiographic units. This variety, expressed in terms of morphogenesis (agents, processes, and induced forms) or morphodynamics (as response to lithological constrains, structural conditioning, morphometry, or specific triggers) requested numerous calls to find the most suitable classification. While the first attempts (1910–1960) to provide eloquent classifications were following a bottom-up approach, starting with single scattered cases meant to allow regional generalizations, the latter (1960–1990) studies aimed at establishing not only regional descriptions but also national evaluations. This allowed the contemporary (2000 onwards) studies to follow top-down approaches, supported by more accurate statistic or probabilistic models of future slope evolution, focused on homogeneous morphostructural units, representative catchments, or different-level administrative units.

The dawn of Romanian geomorphologic literature on landslide systemic shows significant imports from geology, as actually registered worldwide. The first classifications are not only in agreement with the international ones, but they even precede them sometimes. The lithological predisposition, the structural constraining and, as a result, the landslides’ morphology represented long time the main criteria taken into consideration in landslide classifications. In this way, the geomorphological school gained a strong ability to perform different-scale mappings, but for a long period it did not make significant progresses towards morphodynamic evaluations. The opening of new research centers (Pângăraţi, Pătârlagele, Perieni, Aldeni) during the 6–7th decades of the twentieth century created propitious conditions for more in-depth studies, which provided an important insight into the succession of agents-processes-forms, allowing the first empiric quantitative evaluations on landslide morphodynamics.

For a long period of time, landslide geomorphology in Romania was predominantly descriptive. Regional classifications were only taking into consideration such criteria as morphology or morphography, while elements such as depth, age or degree of activity were only subsidiary. This is the main reason for which, for a long period, terms like mound, step, nest, wave, tongue were prioritarily used in landslide description. Slowly but steadily, considerable progresses are being achieved along the fundamental direction, Romanian geomorphologists providing more accurate and in-depth morphogenetic explanations on numerous scattered cases, allowing a better regionalization of similar processes. On the other hand, the socio-economic environment, focusing increasingly more on land reclamations and on the assessment of optimal land use for an increased economical productivity, enhanced the interdisciplinarity in landslide studies. This process helped the geomorphologists to improve systematic landslide by taking into consideration criteria coming still from geology (including engineering geology) or newly-developed fields like remote sensing and aerial photo interpretation. As a result, criteria such as age, morphodynamic patterns, multitemporal distribution appeared in landslide classification alongside more detailed descriptions of their reasoning.

Encouraged by the increased accessibility and opening towards the modern literature registered after 1990 and supported by the technological (hardware and software, in situ or remote measurements devices) progresses, the landslide geomorphology of the last two decades almost completely shifted approaches, changing from fundamental aspects to predictive studies, in form of susceptibility, hazard, and risk. In the attempt to align itself to the mainstream, the classifications used nowadays are following those used in the state-of-the-art international literature, allowing a common language extremely useful in the international and interdisciplinary modern risk management and communication frameworks.

An overview on Romania’s territory is showing several areas (Fig. 11.12) which are differently affected by specific landslide types. Favored by the lithology, conditioned by structure and morphometric traits, prepared by the different patterns in land use and land management and triggered by precipitation and earthquakes, the landslides may be clustered into several representative units, as follows:

Fig. 11.12
figure 12

The distribution of most landslide-affected physiographic units of Romania (to see the text for other explanations)

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  1. 1.

    The Subcarpathians. Presenting heights of up to 900 m, the hilly Subcarpathian chain is featuring morphometrical traits induced by the loose Neogene (Mio–Pliocene) molasse deposits (dominated by schistose marls and clays in association with sands and gravels), highly folded, and densely faulted. Besides the litho-structural and morphometrical favorability, the intense neotectonic movements (uplift rates of 3–5 mm/year) and high sub-crustal seismicity (characterizing especially the Curvature sector) augment the overall denudation potential, inside which landslides plays by far the most important role. The most widespread types are the shallow translational (seldom rotational, either caused by river undercut or by clayey lens inside thick sands and gravels deposits) slides, affecting the soil and partially the upper part of the regolith. Together with the earth flows, they show a very high frequency but low magnitude, still affecting, as single processes, areas up to 5–10 ha. The slides occur mainly during the spring (rain showers overlapping snowmelt) and autumn (long-lasting rains), while the earth flows show a pulsatory behavior, answering rather fast to torrential summer rains. Conditioned by the illite/montmorillonite/smectite rich clays, the earth flows are featuring a visco-plastic behavior and high speed (up to 20 m/h) displacements. The other landslide types are less represented; however, they may be encountered throughout the entire unit due to the extremely heterogeneous lithology, structure, and morphometric traits. Flash floods are characteristic of the contact area with the Carpathians and meanwhile, the presence of large depressions with extended flood plains alternating with narrowing river sectors contribute to increasing flood potential. Both situations are leading to the occurrence of a large number of riparian landslides (in the form of shallow translational earth and debris slides or rock slumps). Large deforestations are enhancing the potential of slope failure.

  2. 2.

    The Moldavian Plateau. The typical plateau homocline structure imprints the main morphological characteristics of the large number of landslides recorded here, mainly as a result of the lithological favorability (an alternance of consolidated—schistose sandstones and limestones—and unconsolidated—clays, marls, sands, silts—rocks). The predominant NW-SE homocline inclination (inside which several subunits may be separated) is conditioning landslide typology: along the north and west-facing cuesta escarpments occur numerous shallow and deep-seated rock slumps (frequently combined into complex landslides, potentially-affecting the entire slope), while along the dip slope are registered mainly shallow and medium-seated slides and less often earth flows. To this situation contributed significantly, the land-use changes throughout the time, in one of Romania’s most important agricultural regions: deforestations, lack of extended, and well-maintained agro-technical and land reclamation works, property fragmentation. A detailed insight is provided within Chap. 12, this volume.

  3. 3.

    Transylvanian Depression. The region is representative for a particular type of landslides, i.e., glimee (in Romanian). This type of landslides appears also in other regions of Romania (for example, Moldavian Plateau) but found in several plateau subunits of the Transylvanian Depression the optimal occurrence environment. Placed somewhere at the border between spreads and complex, glimee are usually displaced as parallel successive rows throughout the upper half of the slope, rarely reaching the valley bottom. Showing a high magnitude (deep-seated and extended across hundreds and thousands of hectares) pattern, these old (almost entirely dormant or relict) landslides are associated with shallow translational slides (either as first time failures or subsequent reactivations) and rock slumps. The latter are characterizing the cuesta escarpments that are bordering the major rivers crossing the plateau, playing a major role in the evolution of such lineaments. The presence of salt deposits adds dissolution as an enhancing factor of slope instability.

  4. 4.

    The Flysch Carpathians. Especially throughout the Eastern Carpathians, built on Cretaceous and Palaeogene flysch deposits, one may encounter a large number of deep-seated landslides, mainly in the form of translational rock block slides and rock slumps. Showing a high magnitude (frequently above 1–3 mil. m3) but low frequency (tens of years), these processes are characterizing mainly the outer (Paleogene) flysch units, built on looser formations (alternation of less cohesive sandstones with schistose marly and clayey intercalations). Today present in the form of relict and dormant deposits (almost entirely covered by old forests), these deep-seated landslides are marked by numerous reactivations, especially due to river undercut, since the large accumulation deposits frequently reached the valley bottom, causing river blockages and forming landslide dams. The morphology of numerous such landslides is showing a potential seismic implication and may rank them as co- or post-seismic landslides. The presence of large scarps in the immediate vicinity of ridge-tops and crests, close to fault line lineaments and the accumulation sector showing no primary interaction with the river network are standing as potential proofs for earthquake-induced landslides. The overall potential of such slope failures is enhanced by the active deforestations that are characterizing the period of the last 20 years.

  5. 5.

    The Getic Piedmont. The relatively large number of landslides inside this unit may be related as well to both natural and human conditions. On one hand, shallow and medium-seated translational slides occur frequently in the higher part of the piedmont, on clay and marl deposits which are containing sand and gravel intercalations. Usually, they are associated also with erosion forms and processes. On the other hand, high densities of landslides may also be found in the coal-mining fields, on the artificial slopes of quarries and sterile heaps or caused by the presence of underground mining galleries or old ventilation shafts. Deep-seated rock slides (mainly rotational) have a large development along the cuesta scarp slopes bordering the main rivers.

  6. 6.

    High (mainly crystalline) Carpathians. Widely scattered above 1800–2000 m a.s.l., the steep slope of the Carpathians Mountains (built on crystalline rocks, conglomerates, limestones—sone ridges even below 1800 m, and cohesive sandstones) are prone to a wide range of fast-moving landslides like rockfalls, rock avalanches, debris flows, or rock topples. Additional processes like snow avalanches and flash floods are sometimes interacting with landslides, causing severe damages. Especially rockfalls are representing a continuous threat along the main transportation corridors crossing the Carpathians. More detailed information on the predisposition, preparing, and triggering factors of such processes are provided in Part II of this volume.