This study was financially sustained by the IFA‑CEA project no. C4‑08/2014‑2016, 'Climate change teleconnections between Western and Eastern Europe based on speleothem records of the Last Interglacial in France and Romania (FREem)'. The authors are grateful to M. Stoica from the University of Bucharest for great support during the field work and constructive discussions on the tectonic evolution of the study area. V. Drăgușin is acknowledged for improving suggestions and English proofing, I. Șandric for providing a part of the materials, L. Faur and A.L. Cercleux for French proofing. We thank P.G. Salvador from the University of Lille for assistance during the editorial process, C. Ek from the ULG‑Liège University and an anonymous reviewer for constructive remarks which helped us to improve the paper content.
1Scarp retreat is a typical geomorphological process which develops in sedimentary bedded structures, driving the evolution of landscape by continuously consuming the area of the steep outcrop (Schmidt, 2004). It is known as the slope‑parallel recession of a resistant caprock that terminates any elevated, plateau‑like landform. Although largely approached by studies based on the evolution of escarpments in arid environments (Howard and Selby, 1994; Gutiérrez et al., 1998; Gutiérrez, 2012), the mechanisms which drive the scarp retreat process of homoclinal limestone ridges in temperate mid‑latitudes are quite similar (King, 1975). By observing the longitudinal morphology of a retreating scarp, two essential components are distinguished: prominent ridges or slope fragments usually subjected to slumping, and a number of steep dry valleys dissecting the scarp, tightly connected to the presence of fractures and faults. The steep dry valleys result from the common acting of various weathering and gravitational processes particularly developed on limestone. Since the limestone behavior to weathering processes (including chemical weathering by dissolution) is unique among the various rock types, the dry valleys carved in such bedrock exhibit a particular evolution and morphology.
2Preliminary studies on the Vânturarița‑Buila Massif in the South Carpathians, Romania have previously reported the presence of numerous steep, short valleys dissecting the retreating scarp (Călin, 1988; Badea et al., 1998; Tîrlă, 2012). In the Romanian karst literature these minor landforms are called “hornuri” (not to be confused with the English term “horn”, which means “a prominent sharp peak usually shaped by glacial processes” (Embleton and King, 1968). In karst terminology, the term “dry valley” is accepted for this type of landform, considering that “not all valley forms on limestone are necessarily the result of fluvial erosion and slope wash” (Sweeting, 1972).
3The specific morphological patterns of the small dry valleys in Piatra Craiului Massif were described in detail by Constantinescu (1997, 2009). He defined the “horn” as a 1st order elemental valley in the Horton‑Strahler classification system, very short (50‑100 m), narrow (5‑10 m) and steep (average slope > 60°). However, these values should not be fully considered, as in reality there are numerous exceptions in the natural environment. The “chimney”‑type, concave‑up linear landforms dissecting the NW‑facing scarp of the Vânturarița‑Buila Massif were hereafter referred to as steep dry valleys (SDVs).
4The spatial distribution of steep dry valleys in limestone ridges or massifs reflects a specific stage in their evolution. Apart from the interaction of tectonic and gravitational processes and forms, karstification has a significant contribution. The presence of speleothems (terrestrial archives of paleoenvironmental information) is related to the arrangement of joints and faults network, hence – to tectonics. The SDVs develop along these tectonic features during the scarp slope retreat and expose the gradually unearthed speleothems.
5The main purpose of this paper is to study the morphometry and development of steep dry valleys in relation to structural patterns given by tectonic fractures and faults in a retreating limestone scarp. We also outlined the importance of SDVs in providing supplemental environmental information compared to other mountain areas, especially in the Carpathians. Orientation‑based structural analysis shows the relations between spatial distribution of SDVs, fractures and faults. Geomorphological analysis of SDVs longitudinal profiles revealed an interesting correlation between the limestone caprock thickness – inferred from SDVs ground lengths – and the arc radius of the amphitheater‑shaped scarp they dissect.
6The Vânturarița‑Buila Massif is a sub‑unit of the Căpățânii Mountains, located in the central part of Southern Carpathians (Romania) (fig. 1‑2). It is a massive SE‑dipping hogback, a limestone‑capped ridge with a dominant NE‑SW direction given by the initial setting of the Getic Nappe over the Danubian basement unit. Geology consists in a thick overthrust sheet of metamorphic rocks of the Median Dacides basement (Getide terranes) in the South Carpathians (Săndulescu, 1984; Balintoni, 1997). Dominant rocks in the Getic Nappe outcropping beneath the major escarpment include paragneiss, amphibolite and eclogite stripes (Oncescu, 1965; Iancu et al., 1998). A 250‑300 m thick layer of massive reef limestone of Kimmeridgian‑Tithonian age from the sedimentary cover of the Getic Nappe lies upon it (Mutihac and Mutihac, 2010). It outcrops only in the south‑eastern part of Căpățânii Mountains because of a local tectonic uplift of the basement and forms the prominent ridge of the Vânturarița‑Buila Massif. Limestone sequences in the Vânturarița‑Buila Massif are remnants of the Getic Carbonate Platform, which occurs throughout the South Carpathian Domain (Patrulius, 1976). The entire mountain front is composed of tectonic compartments separated by NW‑SE oriented strike‑slip and dip‑slip faults. A major NE‑SW segmented fault separates the Vânturarița‑Buila Massif in the Getic Domain from the molassic Olănești Hillocks in the Dacian Basin.
7The steep dry valleys incised into the limestone caprock are closely related to scarp retreat process. Most of them are located on the NW‑facingmajor scarp; other valleys developed on the prominent opposite scarps in “Curmătura Builei” (Buila Pass); and very few are fault‑related, dissecting the major fault scarps on the SE‑facing slope.
Fig. 1 − Geographic setting of the Vânturarița‑Buila Massif.
Fig. 1 − Situation géographique de Massif Vânturarița‑Buila.
A. In the Căpățânii Mountains and B. In the Romanian Carpathians. C. The digital elevation model was created on the basis of EU‑DEM (GMES RDA Project, Copernicus Programme), with a 25‑meter resolution.
A. Dans les montagnes Căpățânii B. Dans les Carpates roumaines. C. Le modèle numérique de terrain (MNT) a été réalisé sur la base du projet EU‑DEM (Projet GMES RDA, Programme Copernic de l'Union Européenne ‑ 2015), avec une résolution de 25 m.
Fig. 2 − Basic geology of the area and distribution of the scarp‑related steep dry valleys (modified after Lupu et al., 1978).
Fig. 2 − Géologie simplifiée de la zone d'étude et distribution des vallées sèches escarpées formées par retrait de l'escarpement (modifié d’après Lupu et al., 1978).
8The inventory, mapping, morphometric analysis and relationship with tectonics of the scarp‑incised dry valleys were based on field research and DEM analysis. Orthorectified aerial imagery was used to identify and extract the valleys, as well as to comparetheir resulted lengths to field measurements. The total number of dry valleys found was 58, although only 47 are located on scarps and therefore considered in this analysis. They were numbered V1 to V47. The geological map at a scale of 1:50,000 provided several major NW‑SE‑ and NE‑SW‑oriented faults and fractures which helped sketching the main tectonic framework of the massif. A number of 300 faults and fractures were identified and manually extracted from the aerial imagery. As well, the major faults documented on the geological map at the scale of 1:50,000 (Lupu et al., 1978) served as tectonic landmarks. Orientations of fractures, faults and steep valleys were calculated using the EasyCalculate 10 tool in ArcMap (Tchoukanski, 2010). Rose diagrams were constructed in order to perform a comparative structural, orientation‑based analysis on the two datasets ‑ steep valleys and tectonic structures ‑ and observe the relations between joint and fracture systems and valleys formation.
9We identified the linear patterns of the steep valleys using the longitudinal profiles extracted from a medium‑resolution DEM, created by interpolating elevation values of contour lines from the 1:25,000‑scale topographic map. We calculated the following morphometric parameters of the linear valleys: maximum and minimum elevation, elevation range (ΔH), length, average and maximum slope, maximum slope length, and azimuth. Field measurements were applied on 8 prominent valleys grouped on the north‑western slopes of the Albu, Buila and Vânturarița mounts. The statistical analysis shows the role of median in outlining the particular morphometry of each group (tab. 1). During field research, a GPS device (eTrex Vista® Hcx by Garmin) and a Freiberg geological compass were used. Field geomorphological mapping of the ridge‑top was systematically carried in order to identify related karst landforms (sinkholes, potholes, crevice‑type caves) and deposits (speleothems).
Tab. 1 − Synthetic statistical data on the morphometry of steep dry valleys in the Vânturarița‑Buila Massif.
Tab. 1 − Données statistiques synthétiques de la morphométrie des SDVs dans le massif de Vânturarița‑Buila.
The values represent the median of each morphometric parameter.
Les valeurs représentent la moyenne de chaque paramètre morphométrique.
10The major NW‑facing limestone scarp and the small opposite fault‑related scarps in central area of the massif (Buila Pass) are dissected by a total number of 47 steep dry valleys. These minor landforms indicate the most retreated sections of the limestone scarps. We synthesized data by grouping the SDVs according to their spatial distribution and calculating the median values of the key morphometric parameters (tab. 1).
11The highest elevations are reached in Mt. Vânturarița (1789 to 1872 m), and the lowest in Mt. Stogșoare (925 to 1127 m). To the northern extremity, Mt. Stogu (1494 m) stands as an insular remnant of the carbonate platform. Here, elevations of the dry valleys range between 1228 m and 1350 m. The difference in elevation (ΔH) between the top and the base of a steep dry valley developed in caprock is especially suggestive about the exposed caprock thickness in that section. Its role will be further discussed in this paper in relation to tectonic control over the scarp retreat process. Most values of ΔH range between 50 and 170 m, with extremes around 10 m and 200 m. Several patterns are observed in their distribution. Moderate differences, hardly exceeding 100 m, were found in Mt. Vânturarița, the highest area of the massif. Very high values occur in Mt. Stogșoare, a tectonic block which stands at the lowest elevations (950‑1150 m): over 200 m in elevation range.
12Directly related to vertical difference, the longest SDVs occur in the Stogșoare area (~150 to ~270 m), deeply incised by the Cheia River, and in Mt. Buila‑Albu (~230 m). The latter developed in the limestone caprock. By comparison, the steep dry valleys in Mt. Vânturarița are surprisingly short (~100 to ~140 m) regardless of the fact that it reaches the highest elevations in the entire massif. Similar to the elevation difference, the length of SDVs is directly proportional to the thickness of exposed Jurassic limestone caprock. It varies according to the tectonic pattern of the landform: the uplifted metamorphic blocks are thinly capped by the bedded limestone, whereas the subsided blocks bear a thicker stack of carbonate rocks.
13Slope is an essential morphometric parameter of the SDVs and is commonly high, according to the parallel‑retreat character of limestone caprock. The valleys are steep, with average slope ranging between 35° and 50°. The 'Hornurile Popii' tectonic‑karst corridors in Mt. Piatra are atypical dry valleys. Their development might be due to some parallel reverse faults probably inherited since the Late Cretaceous tectogenesis (Iancu et al., 2005). Tectonic relaxation related to post-Sarmatian extensional events, and then controlled by the scarp retreat process, has moved the fault walls off from each other and the deep dry valleys formed. Maximum slope usually exceeds 40° and even 60°, except for the tectonic‑karst corridorsin Mt. Piatra, with 25°‑30°. The azimuth pattern was included in the structural analysis, in relation to tectonic features.
14The morphometric patterns of the SDVs were graphically illustrated on the longitudinal profiles (fig. 3). All the profiles were scale‑fit for an easier interpretation and grouped according to their spatial development across the NW‑facing main scarp and the two opposite‑facing minor scarps in Buila Pass.
Fig. 3 − Longitudinal profiles of the steep dry valleys.
Fig. 3 − Profils longitudinaux des vallées sèches (type en 'cheminée').
A‑E. Location of the main groups of dry valleys; F. Convergent dry valleys in Mt. Stogu (1494 m a.s.l.); G. The highest dry valleys, in Mt. Vânturarița (1875 m a.s.l.); H. The longest and steepest dry valleys in Mt. Buila, V22‑V26; I. V23 and V24 expose the most abundant and interesting unearthed speleothems in the Vânturarița‑Buila Massif; J. Gentle‑inclined, fault‑related “Hornurile Popii” corridors in Mt. Piatra. Shaded areas : knickpoints and benches.
A‑E. Localisation des principaux groupes de vallées sèches ; F. Vallées sèches convergentes dans le Mont Stogu (1494 m) ; G. Vallées sèches les plus élevées dans la Montagne Vânturarița (1875 m) ; H. Les longues vallées sèches et escarpées du Mont Buila V22‑V26 ; I. V23 et V24 comprennent les plus abondants et intéressants spéléothèmes (exhumés) dans le Massif Vânturarița‑Buila ; J. Couloirs « Hornurile Popii » dans le Mont Piatra, en pente douce, formés le long de failles. Les zones ombrées (en gris) : les points d'inflexion et les surfaces structurales.
15Most of dry valleys developed on the NW‑facing limestone caprock have uniform, steep longitudinal profiles, not depicting any significant breaks. Scarp knickpoints and benches appear to be restricted only to V22‑V24 steep dry valleys, on the western flank of Mt. Buila. Here, the landscape has recorded an important stage of the scarp retreat process. Parallel slices detach from the caprock along very deep, arcuate tensile fractures (the “D” scarp sector in Figure 4). Right under the mountaintop, an immense slice has lowered by 2 to 5 meters triggered by gravitational forces and subsequent partial collapse, resulting in a ridge‑top depression associated with double opposite ridges – a structural complex of gravitational origin known as “sackung” (Gutiérrez‑Santolalla et al., 2005). Here we will shortly point out only the implications this sackung complex has on the SDVs differentiate geomorphology.
Fig. 4 − Correlation between the orientations of major faults (in grey), tensile fractures and minor faults (in black) and steep dry valleys (in red).
Fig. 4 − Corrélation entre la direction des failles principales (gris), les linéaments tectoniques (noir) et l’orientation des vallées sèches escarpées (rouge).
16V22, V23 and V24 are parallel, side‑by‑side steep dry valleys formed at the western edge of the ridge‑top depression on Mount Buila. The collapse origin of this depression is also supported by the subsurface morphology and surface discontinuities found in the upper sector of the steep dry valleys. Crevice‑type caves or gull caves with typically unstable breakdown morphology have developed deep down under the depression. The entrance in the Collapsed Cave (cadastral number 2044/7; Emil Racoviță Institute of Speleology, 2016), the largest crevice‑type cave in Mt. Buila, is located at the upper end of V23, at 1817 m a.s.l. (value obtained by GPS measurement).
17The cliff‑and‑bench topography of the three steep dry valleys (V22, V23, and V24) is controlled by gravitational processes. The similar knickpoints and benches identified at 1750‑1760 m on the longitudinal profiles of V22 and V24 indicate the depth of collapse deformations, ~70‑80 meters. In case of V23 (which is different because it formed on the exposed caprock of collapsed slice, at the western edge of ridge‑top depression), the knickpoints and bench at 1790‑1810 m point out the development of another step at ~30 meters below the bottom of depression. A direct relationship exists between the underground morphology of collapse caves and geomorphology of SDVs revealed by longitudinal profiles.
18Overall, correlation of all the analyzed longitudinal profiles of the steep dry valleys provides geomorphological information of the entire limestone scarp.
19In order to calibrate the data obtained by DEM processing, 8 of the most representative dry valleys were sampled. All of them are located on the retreating scarp. Azimuth and slope field measurements were tested on each of them and the values were compared to those extracted from the DEM in Global Mapper application (tab. 2).
Tab. 2 − Comparative DEM‑ and field‑based measurements on the morphometric patterns of steep valleys (all values are given in degrees).
Tab. 2 − Comparaison entre les mesures extraites du MNT et celles mesurées sur le terrain concernant les types morphométriques des vallées abruptes (toutes les valeurs sont en degré).
20The differences between values (ΔA, ΔS) represents data precision (up to ± 2° for azimuth and up to ± 7.6° for slope) and are rather caused by application errors, largely given the low field accessibility and the complex morphology of the scarp slope, to which adds the obstruction caused by the natural vegetation abundance. Data accuracy is higher for the azimuth values, considering that orientations extracted both from the topographic map and the orthorectified images are more accurate than those measured directly in the field. For slope and longitudinal profiles extracted from the DEM, the accuracy is somewhat problematic because of its medium resolution. However, the accuracy assessment showed that the method is qualitatively superior to field measurements.
21The development of most SDVs was favored by the tectonic features, such as tensile fractures and strike‑slip faults, which were already documented in the Vânturarița‑Buila Massif (Tîrlă and Vijulie, 2013). One could notice that where a fault or tension fracture intersects the scarp, SDVs occur. The degree of fracturing in a scarp is highly significant to its retreat rate; hence fracturing largely determines its resistance to erosion (Gutiérrez, 2012).
22Clayton's statement that “[...] every fault line is the locus of a dry valley and their formation by frost and snow action is a possibility” perfectly applies to SDVs in the Vânturarița‑Buila Massif. He also affirms that “disintegration of limestones by frost is particularly accelerated along fault and joint‑lines” (Clayton, 1966). In geomorphological sense, the process develops along the scarp‑related steep valleys, where rocks are loosened by freeze‑thaw action.
23An orientation‑based structural analysis involved two datasets linked to tectonic (faults and fractures) and geomorphic features (steep dry valleys) in the Vânturarița‑Buila Massif (fig. 4). N1‑3 represents the total number of features analyzed. The bin size is 10 degrees, and the dashed arcs correspond to amphitheater‑shaped scarp sections lettered A‑E. One could notice at first glance that the tectonic network is well organized into an orthogonal pattern. Reverse faults, tension fractures and joints are preferrably NE‑SW oriented, and dextral strike‑slip faults run perpendicularly on a NW‑SE direction.
24Although the anisotropic properties of the SDVs’ spatial distribution are influenced by fault and joint orientations, they depend on the morphology of the retreating scarp. Several individual amphitheater‑shaped headwalls can be observed on the map in Figure 4. They are outlined by dashed half‑circles between the Piatra and Vânturarița peaks. Rounded shapes are typical for slopes undermined by combined groundwater sapping and mass wasting processes (Howard, 1995; Laity, 2008). Individual drainage systems form at the caprock basis of the Vânturarița‑Buila Massif, where springs emerge. The limestone caprock lacks an organized drainage network, though infiltration water is consistent. But we consider that the greatest influence is of tectonics, and less of other mechanisms. The Vânturarița‑Buila Massif is 'cut' into quasi‑parallel slices by transversal dextral strike‑slip faults (fig. 2), denser to the north of Buila Pass, in Mt. Albu, Buila and Vânturarița, and sparser to the south, in Mt. Piatra. The scarp has an amphitheater shape where the strike‑slip faults are denser, but this shape is loosened where faults are remote to one another. Then, freeze‑thaw action and mass wasting complete and polish the rounded‑shaped scarp.
25Thus, regardless or slightly dependant of the obvious tectonic control, the amphitheater‑shape typical for a retreating scarp induces the rounded arrangement in SDVs spatial distribution. A remarkable pattern was observed in the arcs size. The long‑dashed arcs outlining the rounded‑shaped scarp in Mt. Albu and Mt. Vânturarița have a radius of ca 0.45‑0.5 km. A larger, ~0.65 km‑sized arc radius, is prefigured in Mt. Buila by the tension fracture system (the short‑dashed arc). Instead, to the south‑west, the minor opposite‑facing scarps in Buila Pass describe smaller arcs, with radiuses of 0.26 to 0.38 km (fig. 4). We presume that variations in size of the amphitheater‑shaped scarps are related to the base of the scarp undermined by seepage water sub‑sapping and mass wasting. In other words, the scarp’s height is directly proportional to the amphitheater‑shape size. For example, amphitheaters in the Colorado Plateau range from several hundreds of meters, where they are shaped into a specific rock layer, to tens of kilometers in size, comparable to the outstanding thickness of various sedimentary layers. Only to verify our assumption, we sampled five amphitheater‑shaped scarps from the Colorado Plateau and included them into our analysis. Four scarps (named Colorado‑1 to Colorado‑4 in Table 3) have smaller arc radiuses (< 1 km), are cut into the lower Tapeats Sandstone (Karlstrom et al., 2012) and represent the steepheads of elemental valleys. The fifth scarp (Colorado‑5) cuts the middle sedimentary sequence of the Colorado Plateau (i.e. the Temple Butte, Redwall and Surprise Canyon formations) and has an arc radius of 2.7 km. The pattern also applies to submarine landforms; a 55‑km amphitheater‑shaped scarp was crowned on the northern insular slope of Puerto Rico, from a water depth of 3000 m to 6700 m, after a giant submarine slope failure (Schwab et al., 1991). We synthesized all data in Table 3. The related graph depicts a remarkable correlation between the size of arc radius corresponding to amphitheater‑shaped scarps and the caprock thickness (fig. 5). A detailed analysis of more sampled scarps developed in caprocks of various thicknesses and resistance is useful for strengthening this assertion.
Tab. 3 − Variability of exposed caprock thickness and the arc radiuses of scarp sectors at different scales in the Vânturarița‑Buila Massif, Colorado Plateau and continental slope of Puerto Rico.
Tab. 3 − Variabilité de l’épaisseur de l’abrupt et du rayon des arcs de cercle circonscrits aux secteurs escarpés en forme d’amphithéâtre, mesurée à différentes échelles dans le Massif Vânturarița‑Buila, le plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.
Fig. 5 − Correlation graph between the caprock thickness and the arc radiuses corresponding to amphitheater‑shaped scarps in Vânturarița‑Buila Massif, Colorado Plateau and the submerged slope failure in Puerto Rico.
Fig. 5 − Graphes de corrélation entre la hauteur de l’abrupt et les rayons des cercles circonscrits aux secteurs d’abrupt en forme d’amphithéâtre du Massif Vânturarița‑Buila, le Plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.
A. Of each sample; B. Of all data. In case of Vânturarița‑Buila Massif, the exposed caprock thickness was inferred from the medians of SDVs lengths.
A. Données des unités géographiques ; B. Toutes les données. Dans le cas du Massif Vânturarița‑Buila, la hauteur de l’abrupt (épaisseur du toit de la formation rocheuse) a été obtenue à partir des valeurs médianes de la longueur des vallées sèches abruptes.
26The elevation range (ΔH) between the basis and the top of SDVs (tab. 1) is therefore relevant to estimate the size of amphitheater‑shaped scarp. It also indicates the thickness of the outcropping limestone caprock, ranging between ~50 m in Buila Pass and 107‑136 m in Mt. Albu, Buila and Vânturarița. We can observe that the median values in Buila Pass (56 m in Mt. Piatra NE‑facing scarp, and 86 m in Mt. Albu SW‑facing scarp) are almost half of the ones in the central part of the massif (tab. 3, fig. 5).
27Limestone provides an advantage in addition to other types of rocks: the presence of speleothems as terrestrial proxies, climatic and tectonic archives containing information on the landscape evolution. In limestone ridges, steep dry valleys develop on the retreating scarp preferentially where crevice‑type caves or relict karstification levels intersect the topographic surface, becoming exposed. This is explained by the fact that they formed under the control of strike‑slip faults and tension fractures, which provided the pathways for water infiltration and circulation into the rock mass. Initially, small sinkholes and potholes occur and develop on the ridge top; then, as the scarp retreats, these open into the linear steep dry valleys. Further, weathering and mass movements continue to shape the slope profile. As scree covers a part of the 'horn' base, this becomes inactive and the SDV continues to develop only on the caprock outcrop, simultaneously with the slope retreat. Fluvial processes gradually remove the scree, given the trend of achieving equilibrium of the slope profile.
28According to Necea et al. (2005), a tectonic rebound occurred during the Late Pleistocene until present‑day. The Carpathians uplift resulted in the reactivation of ancient faults. In the mountain environment we discuss, gravitation and karstification combined have enlarged some of the inherited longitudinal faults and opened new cracks which they modeled, resulting crevice‑type caves or gull‑caves. These usually occur within the first 0.5 km from the scarp margin (Farrant et al., 2014). This type of cave is common in the Vânturarița‑Buila Massif, where low thickness of limestone caprock and high structural dip inhibited the development of large karst systems. The bedded structure of limestone has favored the development of a stepped crevice to the size of a cave – a crevice‑type cave, very similar to the model advanced by Margielewski and Urban (2003).
29Consistent radiating fibrous aragonite and calcite layers grew on the fault walls in Mt. Albu and Mt. Buila, a phenomenon favored only by extension. In some cases, the amount of horizontal extension is given by calcite layers thickness. Uncommonly abundant and well‑developed speleothems were found at the top of V24 steep valley in Mount Buila, at 1810 to 1820 m a.s.l. Since there is not any (allochthonous) river nearby, karstification has most probably developed in a tensile crevice system deep inside the limestone bedrock throughout the Pleistocene, under stable environmental conditions. As the mountain uplifted, speleothems were progressively exhumed and unearthed by weathering, long after their growing has ceased. Certain results can be achieved during future research from U‑series dating and isotopic analyses. In this study, we established a correlation between the spatial development of the steep dry valleys and the presence and abundance of these calcite deposits.
30Tectonics controls the scarp retreat by major and minor mass movements. Minor mass movements consist in small rockfalls, scree transport and deposition along the steep valleys. Instead, the DSGSDs (deep seated gravitational slope deformations) are major mass movements which occur in response to disturbance of slope equilibrium (Margielewski and Urban, 2003). They are the main processes controlling the scarp retreat. The tension cracks that precede the formation of head‑scarp are scarp‑parallel and very deep; when they open and widen, the 'crevice‑type caves' form. The DSGSDs in Mount Buila host a great variety of exposed and underground landforms: ’chimney’‑type, steep dry valleys with abundant speleothems and giant aragonite‑to‑calcite deposits on the fracture walls, collapse 'crevice'‑type caves, sackung and sackung features (uphill‑facing scarps), etc.
31The karstifiable nature of limestone bedrock is a plus advantage to observing underground morphology; typical karst processes and speleothem formation turns simple crevices into real caves. In limestone ridges, scarp retreat is a process by which the access to environmental archives stored by the tectonic lineaments network is provided through SDVs development, which retreat jointly with the scarp.
32Knowledge on the general and detailed morphology of a retreating scarp is practical for further research on its geomorphological, paleotectonic and paleoclimatic landscape evolution during the Quaternary.
33Morphometric data of the steep dry valleys in the Vânturarița‑Buila Massif (South Carpathians) provide information about the geomorphic processes involved in scarp retreat. Faults and tensile fractures control the spatial distribution and morphology of the steep dry valleys developed on the exposed caprock. These valleys reflect a certain evolution stage of tectonic‑karst landforms related to the normal scarp retreat process. The cliff‑and‑bench topography of several SDVs in Mount Buila is determined by gravitational processes (especially collapses) that act upon the limestone caprock and control its retrogressive evolution, particularly dynamic in this part of the massif.
34The major transversal strike‑slip faults which separate the tectonic blocks direct the amphitheater‑shape of the retreating scarp. An obvious correlation between the thickness of exposed bedded strata on the NW‑facing steep slope and the circumference of amphitheater‑shaped scarp sections was observed in the central area of the massif.
35The spatial distribution and morphology of the steep dry valleys developed on a retreating limestone scarp is closely related to its normal evolution. At the same time, geomorphological analysis of SDVs can reveal specific patterns of the scarp retreat process in its various stages of evolution.