WATER AND GEOSCIENCE

Assessment and forecast stability of slopes in the Carpathian and subCarpathian area of DâmboviŃa and Prahova. Classification and risk factors

ALEXANDRU ISTRATE, MADALINA FRINCULEASA, GICA PEHOIU Department of Geography, Faculty of Humanities “Valahia” University of Târgovite Str. Lt. Stancu Ion, no. 3436, 130105, Târgoviste, DamboviŃa ROMANIA [email protected]; [email protected]; [email protected]; www.valahia.ro

Abstract: To determine risk factors in assessing and forecasting, the stability of slopes is a need for classification and ranking, so it is possible to establish a degree of urgency in the analysis of paddocks. The paper is addressed to the risk factor of landslides, which affects the slopes of space flyisch and fore syncline of the Carpathian space between rivers Arge and ProviŃa. Analysis of spatial distribution of landslides shows the role of geostructural factor, that has the regional breakdown. Within a geostructural unit, lithologic factor can be considered as constant, no matter at what level scale geological and geochronological formations fall, favoring the occurrence of landslides. Spatial distribution of landslides seems no coincidence, these focusing on certain areas that overlap alignment of tectonic fractures, usually crossing the general geological structure. Therefore, in the researched area, tectonic factor must have a large slope stability assessment and prognosis. In areas affected by tectonic fractures are found to accelerate the process of altering the rocks, which causes a reduction in the resistance forces on the one hand, and increasing gravitational instability, on the other. However, faults and their surrounding areas promote the movement of groundwater, contributing to increased gravitational instability. Distribution analysis of landslides on the slopes is for every slope values that determine the maximum frequency reached for relatively small, up to 150, of flyisch, and up to 300, where is located Carpathian fore syncline. The explanation of such sharing should be sought in the mineralogical composition of the deposits involved in the phenomenon of slip and geological structure of the perimeter analyzed. From here we can see the correlation between various factors which condition each other and form the whole trigger mechanism of landslides.

Keywords: geostructural factors, spatial distribution, frequency of landslides, tectonic factor, illit montmorillonit couple, fault.

1 Introduction climate and hydrological regime, the movement of Slope instability is a constant presence in the of groundwater, seismicity region, arboreal vegetation Carpathian flyisch and foresyncline, being, on the coverage and impact of human activity. one hand, a consequence of natural evolution of Of the more than 150 landslides analyzed over relief, and on the other, a result of human activity on the years include the most detailed elements of a environmental factors. Concerns for the limitation number of 136, which covers the pleated and folded of the effects on human habitat appear to be structures in the space of Carpathian foresynclinal insufficient, and that due to the volume of work that interfluve Arge ProviŃa. Their monitoring was it entails, and thus their costs. conducted over the period 19652000 years. Therefore, it must be taken into account the Preliminary data included their knowledge of problems of assessment and forecasting the behavior their spatial and temporal location, information on of slopes in time, approach that proves extremely gradient slopes and areas affected. difficult and complicated. Just a few of these slides were taken from The assessment and forecast models of slope detailed data in respect of spatial geometry, physical stability are considered eight factors of favorability, and mechanical parameters of the deposits involved namely: arrangement of structuraltectonic, the phenomenon of slip and the geological sub lithologic and petrographical nature, geo layers, hydrological and hydrogeological morphological configuration of the land surface, conditions, analysis of the status of efforts slopes etc.

ISSN: 1790-5095 208 ISBN: 978-960-474-160-1 WATER AND GEOSCIENCE

2 Distribution of landslides By their location in relation to geological 100 structure has resulted in a statistical distribution, which allows some conclusions in the risk 80 assessment and classification of the region. 60 Correlation in distribution of landslides with flyisch 40 units (Fig. 1) and foresynclinal creates an overview 20 of the extent and spatial distribution of the slopes of No. phenomenon. One can easily see that the highest 0 frequency belongs to flyisch, which has values Flisch Fore-deep nearly double (86 landslides) in relation to fore Geotectonic Units synclinal (50 landslides) (Fig. 2). This image allows some comments on favorability factors in landslide Fig.2.Fig. 2. Landslide frequency correlated to the tectonic units occurrence. But within a region with high risk of instability phenomena in the development of the land, it is noted that the distribution and frequency of a certain structure, which should found significant weight factors in assessment and forecast slope instability. For the regional analysis of the phenomena of land instability, lithologic factor has a major share. On the canvas of Ceahlău, land slip processes are located on the Early Cretaceous formations, mainly on marly facies, the marly gritty schists, which are Sinaia layers and Comarnic layers. Spectacular phenomena of instability are giving by posttectonic deposits in the internal party of Ceahlău canvas, belonging Turonian Senonian (Late Cretaceous), in the perimeter Dealul Frumos Runcu. All upper Cretaceous, the period Vraconian Turonian, in the predominantly shale facies, is due to landslides in the Macla and Teleajen canvases, in the line Măgura Fieni Vulcana de Sus. The relative uniformity of lithologic facies in geological structures out lengthwise (from east to

Fig. 1. Landslide repartition in the flysch and west) would suggest that the distribution of foresyncline instability phenomena have the same spatial distribution, with variations depending on local Geostructural speaking, the area covered are conditions (slope, arboreal vegetation coverage, different internal structures represented by the etc.). However, there is a concentration of landslides Ceahlău canvas, Teleajen and Macla canvases, and in some alignments that overlap large tectonic faults external flyisch made here only by the one of crossing. Tarcău. To these are added posttectonic units of Another area with relatively high frequency of internal flyisch such as: syncline Slănic Bezdead instability is the process which overlaps Gura BărbuleŃului, Râul Alb Malu cu Flori posttectonic structures of internal flyisch, Văleni DâmboviŃa and Talea Runcu. consisting of Eocene deposits or Paleogene Lower South of Tarcău canvas develops a foresyncline Miocene of synclinals Râul Alb Malu cu Flori where also the land sliding phenomena have a Văleni DâmboviŃa and Slănic Bezdead Gura certain distribution and frequency. BărbuleŃului. It can be observed the same Therefore, one can say that the regional factor in distribution along tectonic faults overlapping geostructural has a large share of the risk alignments. assessment of landslides and it correctly reflects the A high frequency of landslides is registered in distribution and frequency. the canvas area of the Tarcău of external flyisch, forming a broad waiver, being multiple transverse

ISSN: 1790-5095 209 ISBN: 978-960-474-160-1 WATER AND GEOSCIENCE

faulted. In this case, the lithologic factor favors the posttectonic structures. An obvious example is occurrence of landslides in clayshale facies of Cricovul Dulce Valley, where a series of landslides Pucioasa layers. But, as in the cases listed above, was produced along the fault line upper Viineti, a there is a group of landslides after some alignments. transverse fault of general geological structure of In the foresyncline, lithologic factor remains the Tarcău canvas. A crosscutting aspect have also the main favorability factor by shale facies of Badenian, perimeters of locality Vârfuri and Ulmetului fault, Pontian and Dacian sequence of claysand. located slightly west. But some landslides are grouped, as with fliysch In the same way can be seen sliding Vulcana Băi of some areas, although the area of outcrop of village perimeter, following, more or less, the fault geological formations that favor the occurrence of of IalomiŃa. landslides is much higher. Quaternary, especially the Piedmont area of 60 50 Cândeti developed interfluve DâmboviŃa Arge, 40 favoring instability phenomena through 30 intercalations of clay and clayshale of Cândeti 20 10 facies. In this case, should be considered also hydro No. of slopes of No. 0 geological factor, which has a special weight CRETACEOU PALEOGENE PLIOCENE QUATERNAR because of the presence of aquifers under pressure. S Y

3 Distribution of landslides in relation to geological formations Time scale Distribution of landslides in geological formations allows some comments (Fig. 3). The Fig.Fig.3. 3. The The distribution distribution of ofthe the landslides landslides according according to tothe the geological formations analysis of this sharing shows the highest frequency geological formations observed in the area of outcrop of Paleogene of canvas Tarcău and posttectonic structures of The role of tectonic factor can be shown also in Cretaceous canvases (50 landslides). A lower the foresyncline, such as northern flank of syncline frequency submit Cretaceous and Pliocene deposits Valea Lungă, where cross faults is related to the (36, respectively 38 landslides), which would extended Tarcău canvas. As can be evidenced suggest that lithologic factor is a constant. tubee fault, along the valley with the same name, is Regarding spatial distribution patterns of extended to the south of Ulmetului fault. Some structures and lithologic complexes ought to landslides from the same flank can be traced to the landslides are located on the eastwest directions. southward extension of the faults Viineti and The situation would be consistent with the broad of Vârfuri. geostructural units, but the reality is different, they Also, in the Moreni town perimeter are some focusing on specific alignments, not incidentally landslides that may be linked with fault of salt in the overlapping large tectonic fractures. northern flank of anticline diapir with the same Returning to Fig. 1, we can notice that the field name. The same situation is encountered in OcniŃa of Cretaceous flysich, Lower Ialomicioara Valley is village area, where are found some slides related to affected by a transverse fault of the geological faults of mounting cross LăculeŃe OcniŃa structure in the sequence along which many Colibai. landslides can be very deep. In this space, canvas of It is to be noticed a differentiation factor in the Ceahlău has a complex structure, given by a distribution of tectonic instability phenomena of the succession of syncline fold, some faulted overfolds, land, explained by the following processes: being affected across the fault of Ialomicioara. The existence of tectonic forces, for mobility To the south, the area of Teleajen canvas, or reactivation of faults of others, which has landslides are located along faults of superposition the effect of changing the status of efforts of at the head of tectonic structures, as in the slopes; perimeters of settlements Cucuteni and Fieni, or the A system of cracks of one side of the fault canvas area in the territory of the localities Macla plane, which results in a decrease in rock and Măgura, on the Bizdidel Valley. strength and acceleration of deterioration Similar situations on can meet in the field of processes; external flyisch, respectively Tarcău canvas and Hydrogeological faults, which also favors the acceleration of deterioration and hence a

ISSN: 1790-5095 210 ISBN: 978-960-474-160-1 WATER AND GEOSCIENCE

decrease in resistance parameters; Increasing the thickness of the altered shell, 70 implying a greater gravitational effort. 60 Thus, within a high risk regions in terms of land 50 instability, tectonic factor can not be neglected, it 40 sometimes having a crucial role in triggering such 30 20 events and, especially, in issuing a forecast behavior Frequency 10 of slopes. Delineation of fractures in a particular 0 area becomes a mandatory action, especially where sub 15 16-30 31-45 peste 45 slopes are now established, but the future instability phenomena may occur. Slope [degree]

Fig. 5. Landslides frequency in the Carpathian fliysch unit Fig.5. Landslide frequency in the Carpathian flysch unit accordingaccording to to the the angle of of the the slope slope 4 The correlation between landslides and slope angle In the case of foresyncline, an important one and subsidence have produced the slopes of up to Distribution analysis of landslides based on slope 0 angle of the slope founds an inverse proportionality. 30 , representing 32%, similar to the previous Specifically, the frequency increases with (Fig. 6). decreasing slope (Fig. 4), which means that the Therefore, regarding foresyncline, slope slope is not a big major risk factor, as specified in inclination express in some measure proportionality the regulations for the development of risk maps to between it and the risk of landslides. slip the slopes. However, such a result must have an 16 explanation. From the analysis pointed graph is 14 0 observed number of 80 cases, the slopes up to 15 , 12 which represents a rate of 59%, 28 cases of slopes 10 0 corresponding to 30 , with a rate of 21%, and the 8 0 remaining 20% returning more than 30 . Frequency 6 4 100 2 80 0 sub 15 16-30 31-45 peste 45 60 40 Slope [degree] Frequency 20 0 Fig. 6. Landslide frequency in the foresyncline according to the angle of the slope 5 0 5 5 1 -3 -4 4 b 6 1 te u 1 3 s s e Returning to Fig. 2, where the frequency of p landslides is higher unity of fliysch, to landslide, Slope [degree] might suggest that the slope would play an important role in triggering landslides. This Fig.4.Fig. Landslide4. Landslide repartition repartition according according to the angle to theof the correlation, regionally, is consistent with the role of angle ofslope the slope slope in landslide occurrence, whereas, in fact, the formation unit slope has a high percentage Breakdown of the two major geostructural units compared with the foresyncline. Therefore, at the analyzed causes the greatest weight to return fliysch, regional level, slope factor can express the degree of compared with foresyncline. In the unit of flyisch, risk of occurrence of landslides. But within a geo the number of cases for slopes of less than 150 is 65 structural unit with a high risk, it is noted that from a total of 91, representing a rate of 72% (Fig. landslides have high frequency on sections of the 5). slope with low gradient. For foresyncline, where are the same slopes, the Factor explaining this behavior is the number of cases is 15, from a total of 44, mineralogical, that the report is determined by illit representing a rate of only 34%. montmorillonit couple.

ISSN: 1790-5095 211 ISBN: 978-960-474-160-1 WATER AND GEOSCIENCE

Numerous laboratory studies was performed on conversion to montmorillonit is produced from top different types of slide show that illit is transforming to bottom, having an important role it rainfall in montmorillonit, which increases under clays fatty infiltration. deposits surrounding sensitive clays, which have a high capacity to absorb water (Fig. 7). Water absorption may be so great that there is a gravity 5 Conclusions water forming an undercurrent. However, the Analysis of landslides in the Carpathian region occurrence of gravitational water greatly reduces of foresyncline and fliysch in the interfluve Arge internal friction and cohesion forces of clay ProviŃa refer some matters which may result in particles. assessment and forecast the behavior of slopes in time. At regional level, geostructural factor has a defining role in zoning a territory, increasing its share with a degree of geological and tectonic complexity. Inside highrisk regions such as fliysch and even Carpathian foresyncline, lithologic factor can be considered a constant in achieving conditions of landslide occurrence. In the area examined was noted that the slip phenomena have a certain distribution in space, which incidentally are associated with large tectonic fractures, with a regional or local aspect. On notice Fig.7. The corellation between flowing limit and the important role of transverse faults deterioration plasticity index landslide Vulcana Bai of geological structure, which would suggest further efforts to introduce changes in steadystate of In this situation occurs hydrogeological factor, slopes. Therefore, tectonic factor becomes the pore water pressure reducing the normal component of gravity and, thus, reducing the especially important in particular for forecasting the evolution of slopes. resistance forces. Very good results were obtained by studying the The role of hydrogeological factor is frequency of landslides based on slopes gradient. accentuated when the groundwater is mineralized, Logically, the slope should have a high proportion especially the sulphate, as in the Paleogene formations of syncline Slănic Bezdead in evaluating of slopes stability in a region. However, to obtain a high frequency of landslides Buciumeni or Râul Alb Malu cu Flori Văleni on slopes of up to 15160, in the case of Carpathian DâmboviŃa. Furthermore, the contribution of fliysch, and in proportions roughly equal to the groundwater mineral fraction accelerates the process slopes of up to 150 and from 15 to 300, in the of transition illit to montmorillonit. foresyncline region. Therefore, triggering landslides on slopes of less 0 The explanation of such behavior is given by the than 15 is explained by an accumulation of factors, contribution of hydrogeological and mineralogical including the hydrogeological and mineralogical factors that have a role in triggering the instability ones, which have a high share. phenomena of the land. Lower frequency of landslides on slopes steeper Therefore, the eight factors that determine slope slope can be explained by several findings of the instability should have a certain hierarchy, some of field and laboratory work. In areas with high slopes, thickness of altered them with regional importance, while others introduce spatial differences and make us shell is lower, hence the lower value of tangential understand that the distribution of landslides is not component of gravity. entirely coincidental. On the other hand, it has to be In other cases, the size composition of deposits is introduced a factor to expressing the effects on the somewhat rough, which gives greater permeability and allows faster drainage of the slope. Thus, human habitat, so that the following classification and ranking of landslides in the degree of urgency in contact time rock water is relatively short, so the taking measures to limit property damage and transition illit montmorillonit does not occur or is human victims. significantly slowed. In connection with those stated, may draw The analysis in this case shows that the attention to the fact that landslides are a major risk

ISSN: 1790-5095 212 ISBN: 978-960-474-160-1 WATER AND GEOSCIENCE

factor in terms of population and human settlements. However, the more susceptible to such phenomena are especially localities in the geographical area of the rivers DâmboviŃa and Prahova.

References: [1] Florea M. N., Alunecări de teren i taluze, Editura Tehnică, Bucureti, 1979. [2] Istrate A., Elemente de prognoză a evoluŃiei versanŃilor, volumul simpozionului “Schimbul de experienŃă al laboratoarelor din construcŃii”, SELC X, ConstanŃa, 1997, pp. 4651. [3] Istrate A., Fenomene de instabilitate a versanŃilor în zona fliului carpatic din interfluviul IalomiŃa Prahova, Analele UniversităŃii Valahia Târgovite, Seria Geografie, Tomul 3, 2003. [4] Istrate A., (2005), The role of the tectonic factor in the distribution of the landslides in the Carpathian flysch from the IalomiŃa Basin, Revista Forum geographic Studii i cercetări de geografie i protecŃia mediului, Editura Universitaria, Craiova, pp. 8388. [5] Istrate A., RepartiŃia spaŃială i temporală a alunecărilor de teren în domeniul fliului i avanfosei carpatice din bazinele IalomiŃei i DâmboviŃei, Lucrările tiinŃifice ale Simpozionului multidisciplinar internaŃional “Universitaria SIMPRO 2006”, Editura Universitas, Petroani, 2006, p. 5257. [6] Istrate A., ChiŃescu Mădălina, Impact of terrain instability on the infrastructure and human habitat of DâmboviŃa County, Romania; determination and classification of the risk, Congress of Geological Society “Engineering geology for tomorrow’s cities”, Nottingham, UK, September 2006, published in April 2007, pp. 131136; [7] Murărescu O., Pehoiu Gica, Impact on the Environmental Factors of the Landslides in the SubCarpathians of IalomiŃa River, Romania, Environmental Science and Sustainability, Proceedings of the 2nd WSEAS International Conference on Natural Hazards (NAHA ’09), Baltimore, USA; November 79, 2009, pp. 116 120. [8] Mutihac V. et al. Geologia României, Editura Didactică i Pedagogică, Bucureti, 2004. [9] Pehoiu Gica, Cristina Muică, Mihaela Sencovici, Geografia mediului cu elemente de ecologie, Ed. Transversal, Târgovite, 2006. [10] Rotunjeanu I., Stabilitatea versanŃilor i taluzurilor, Editura Infomin, Deva, 2005. [11] Săndulescu M., Geotectonica României, Editura Tehnică, Bucureti, 1984.

ISSN: 1790-5095 213 ISBN: 978-960-474-160-1