Assessment and Forecast Stability of Slopes in the Carpathian and Sub Carpathian Area of Dâmbovińa and Prahova
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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 Târgovişte 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 Argeş 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. Key-words: - geo-structural 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 fore-syncline, 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 fore-synclinal insufficient, and that due to the volume of work that interfluve Argeş - 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 structural-tectonic, 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 fore-synclinal 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 post-tectonic 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 fore-syncline 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 post-tectonic 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 - post-tectonic structures of internal flyisch, Văleni DâmboviŃa and Talea Runcu. consisting of Eocene deposits or Paleogene - Lower South of Tarcău canvas develops a fore-syncline 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 geo-structural 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 post-tectonic structures. An obvious example is occurrence of landslides in clay-shale 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 Vişineşti, a there is a group of landslides after some alignments. transverse fault of general geological structure of In the fore-syncline, lithologic factor remains the Tarcău canvas. A cross-cutting 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 Cândeşti developed interfluve DâmboviŃa - Argeş, 40 favoring instability phenomena through 30 intercalations of clay and clay-shale of Cândeşti 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 post-tectonic structures of The role of tectonic factor can be shown