Department of Geography. Valahia University of Targoviste Annals of Valahia University of Targoviste. Geographical Series Tome 13/2013 Issues 2: 88-98 http://fsu.valahia.ro/avutgs/home.html ASPECTS ABOUT PRUT RIVER TERRACES IN ROMANIAN-MOLDAVIAN BASIN SECTOR, WITH SPECIAL VIEW ON GEOMORPHOLOGYCAL PROCESS Florin VARTOLOMEI 1 Spiru Haret University, Faculty of Geography, Email fvartolomei@yahoo.com Abstract Strating with Mio-Pliocene of Moldavian Plateau rising, the old tracks of Carpathian rivers was oriented to South-East direction, following the decreasing and shoreline oscilation. In the same way, but from North direction, the evolution of Prut river was marked. The other valleys was generated later by transformations and re-traking, often visible in landscapes and in hydrographical basin configuration. Stream action, powered by rising of entire area in late Pliocene and Quaternare pariod, was united with versants and interfluves evolution process, so that the old marine acumulation plane was destroyed (the South part of Moldavia was excepted, where interfluves still keep some sections of Romanian-Pleistocene Plain), also replace with derived landforms, mostly sculptural, with hilly aspect, where litologycal and structural particularities of geologycal base was strongly underlined Keywords: valley, terrace, Prut river, paleogeographycal evolution, landforms, floodplain. 1. INTRODUCTION Location and morphometric elements: Prut basin is situated in the eastern part of Romania, being a pool of contact between the Moldavian Plateau, from Romania to the west and Podolia Plateau, from the Republic of Moldova in the east. Evolution and geographical aspects are related to the Moldavian Plateau, some authors considering this unit subdivision of this plateau. Prut catchment occupies in Romania area of 10,970 sqkm and with related areas in Ukraine and Moldova a total of 28,396 sqkm (Fig. 1). Currently, Prut river is the natural border between Romania and Rep. of Moldova with length of 695 km (Vartolomei F., 2003). Geological conditions: under this aspect, Prut basin overlaps three structural units: Moldavian Platform (up to Fălciu - Plopana fault), Bârladului Platform (between Falciu- Plopana and Adjud - Oancea faults) and Platform Covurluiului, each presenting a folded socket configurations covered by a blanket, with parties willing homocline (Bacauanu et al., 1980). The landscape is presented as a set of inter-fluves stretched-looking bridges, hills separated by wide valleys carved in sedimentary monocline. General landscapes orientation to the south - southeast, the same direction as the major valleys orientation, reflects an obvious adaptation to the structure. Monoclinic structure favored the emergence of positive and subsequent valleys (Fig. 2). 88
Fig. 1. Placing Prut river basin in Danube basin (GIS processing vectors of EEA source) The main steps to be taken in morphology, have values of 300-500 m in the north-west, 300-400 m in the central part, 150-200 m in the north-east and south and a relatively balanced distribution. Altitudes above 500 m are few and isolated. The lowest shares are found along the corridor Prut (130 m to Oroftina, 32 m near Ungheni and below 15 m to confluence) (Bacauanu, 1968). Climate: because of its position in extra-carpathian region, away from the influence of air masses from Atlantic Ocean, but wide open to continental air masses action originating from the east, northeast and north, Prut basin receives moderate rainfall quantities. Prut basin, superimposed on the Plain of Moldavia, is directly exposed to continental air masses in which, air from the west descent surrounding physical and geographical units, frequently suffer föehn processes, so rainfall is low, ranging generally around 500 mm (Radauti 564.0 mm, 529.4 mm Iasi) (Bogdan, 2007). 89
Fig. 2. The hydrographic basin of the Prut - general view (GIS vector processing of source www.geo-spatial.org) 2. EVOLUTION OF PRUT VALLEY Since the first studies on the Moldavian Plateau, area including Prut basin, from those of Cobălcescu Gr. beginner, it was shown that the general inclination of the layers that make up the covers this basin is NW to SE, as successive product withdrawal sea. The main rivers follows consistent slope classes. Compared to current knowledge on the basement area, things do not seem so simple, for while the river main flow direction is generally indicated (NW-SE), Moldavian Plateau natural region shows a cross routing to these courses (Muşinschi, 2000). So, Tufescu V. (1946) distinguishes four units (called by the author "zone") of the Moldavian Plateau from N to S, passing the one side of the Prut valley, radial Carpathian arch: a) to north, Plain of Moldavia (consisting of the Jijia and Raut); b) in the middle, the Massif Central Moldavian and Bacu Massif; c) to south Bârladul Hills and Hotărniceni Hill d) the extended zone of Bârladul Hills to lower Siret Plain and Bugeac. In general, the conduct of these natural regions in the form of a central transverse ridges (SW-NE direction) is presented high, bounded on the north and south by two lowland areas. 90
Crossing this ridge, which extends transversely, formed in high regions of middle Moldavian Plateau, the main rivers prints local changes in their courses, in all courses presented approximate N-S direction (from NW-SE to tributary) and valleys with sectors that are narrow, presented like a real "gates" for longitudinal movement (Bacauanu, 1961). Prut valley is suffering a real stranglehold between Tutora and Răducăneni (Tutora s Gate). Floodplain of Prut river, very well individualized, located on the axis of this basin is the largest alluvial plain of the whole area, with widths of 3-6 km up to 10 km, with sectors enlargement (common field Jijia-Prut) or narrow (Cernăuţi s Gate, Tutora s Gate) and lower slopes of up to 0.6 (Bacauanu, 1973). Prut basin formation begins after the Sarmatian regression wich favored, in the upper valley of the Prut, the continental conditions appearance extended gradually to the southwest. In Bessarabia, Upper Prut sector present a plain where denudation processes and lacustrine-deltaic sedimentary as well had the same intake. Shoreline marine basin was located in the north of the Central Moldavian Plateau. In south sea basin was continous, with clays sedimentary process. In Kersonian denudation processes have been intensified in all area, corresponding upper and middle basin of the Prut (Muşinschi, 2000). In the radius of the Central Moldavian Plateau predominate fluvial-deltaic accumulation facies and denudation processes had a minimal contribution. Marine shoreline met in the south of Codrilor Hills. Fluvial network have west-east general direction. In the Pliocene, the recent plain from upper and middle sectors of the Prut basin, the primary fluvial network had north-south direction. Subsequently, this fluvial deposits system have been eroded. They have kept only the Central Moldavian Plateau watershed and in the Lower Prut river crossing in marine deposits. This package consists of fluvial-deltaic seven horizons (Fig. no. 3). The last four are supposed to belong to paleo-fluvial Prut system, which form in the Carpathian Mountains and therefore Bucatciuc et al (1988) attributes the Stolniceni, Buciumeni, Văleni- Leuseni Obileni-Ungheni terrace deposits (Muşinschi, 2000). Fig. 3. Longitudinal profile on Prut river, from entering the country to its mouth (source Muşinschi, 2000, processing after Gojâc, 1964) 91
At the end of the Pliocene began a new stage of development of the region, under the influence of eustatic tectonic movements and several climate cycles succession when exondate surfaces was extended and when the current Prut valley was created. Lithological structure, fossils forms in these deposits and morphological-sculptural character enable us to share the Prut valley evolution in seven phases, spatial limited in line with Black Sea developments. All phases of training valley are summarized in Table. no. 1, where it is possible to catch them in succession from Sarmatian to Holocene. 3. EVOLUTION OF PRUT TERRACES Age, evolution and valleys hierarchy is evidenced by the number and distribution of terraces altitude. They are characterized by a series of fragmented bridges that keeps obvious parallelism with the longitudinal profile of river beds, through a perfect connection of steps along the main valleys and tributaries, as well as by a decrease in the number and altitudes for younger generations of valleys. Table 1. Stages of Prut valley evolution* Sectors Phase Upper Middle Lower MIOCENE Buglovian Basarabian Denudationsedimentary (very lacustrine) Denudation Sedimentary (very marine) Denudationsedimentary (very lacustrine) Sedimentary (very marine) Sedimentary (very marine) Kersonian Denudation Denudation Sedimentary (very lacustrinemarine) PLIOCENE Stolniceni Denudation Denudation Buciumeni Denudation Denudation Văleni-Leuşeni Denudation Denudation Obileni- Ungheni Denudation Denudation Sedimentary (very lacustrinemarine) Sedimentary (very lacustrinemarine) Sedimentary (very lacustrinemarine) (very lacustrine) PLEISTOCENE Văleni Denudation Denudation Denudation Obileni-Slobozia Mare Denudation Denudation Sculeni- Giurgiuleşti Denudation Denudation (very haven) (very haven) 92
Călineşti -Câşliţa Prut Denudation Denudation Chetriş- Giurgiuleşti Denudation Denudation Fălciu-Cahul Denudation Denudation (very haven) (very haven) (very haven) Bolotina- Vetrişoara Denudation Denudation Denudation * after Muşinschi, 2000, with additions A comparative analysis of studies of various authors who have dealt with Prut terraces dating we conclude the existence of two or three steps of meadow and seven or eight terraces relative altitudes up to 160-170 m in Prut Valley and all along Bahlui (Table 2). Table 2. Altitude of terraces on the right bank of Prut* Moldavian Plain Huşi Depression The shedding area V. Băcăuanu I. Gugiuman V. Sficlea T1 10-15 m 5-11 m 8-15 m T2 20-25 m 18-32 m - T3 30-35 m - 30-35 m T4 60 m 57-58 m 60-75 m T5 90-100 m 100-105 m 110-120 m T6 110 m - - T7 140-150 m 134-140 m 130-150 m * benchmarking of studies conducted by different authors Tectonic platform regime with slight epirogenetical Pleistocene lifting, is reflected in maintaining unchanged the relative altitudes of the terraces on the distances of tens and even hundreds of kilometers. In general, all terraces with heights up to 60-70 m are well kept, wider and wider near the confluences (Fig. 4). 93
Fig. 4. Prut terraces map (processing after V. Muşinschi, 2000) Regarding the particle size composition and beds west mobility mostly of the Prut river beds consist of fine sand (0.1-1 mm), have a high coefficient of meandering, surface deformation and depth. The Prut floodplain sometimes occur two to three steps with relative altitudes between 1 and 7 m, cut into the same alluvial complex. These steps with relative altitudes, along them outlines numerous old and abandoned meanders, popin (isle), micro-depressions of terraces, lower areas with excess moisture (Fig. 5). 94
Fig. 5. Morphological elements in the lower Prut - south of Oancea village (processing after 1:25000 scale topographic map) Significant are the old courses called "Prutuleţ" or "old Jijia". Processes and natural forms are modified increasingly stronger through hydrotechnical works or gravel ballast exploitations (the Prut, Jijia). 4. CURRENT ISSUES ON GEOMORPHOLOGICAL PROCESSES Movements of land shapes alike foreheads terraces and slopes of the interfluves. They are facilitated by the geological, hydrogeological, climatic, lithological, morphological and anthropogenic influence. This process contributes to redistribution of the masses of land semi-dynamics and dynamics with various thickness as well as the separation of the rock in situ, at the same time making the transfer to the axis of the drainage of huge amounts of diluvial. Overall, we are dealing with local reactivation of older colluvial masses, but there are cases when gravitational process are very recently activated (Fig. 6). 95
Wingspan most significant have landslides mainly located in the lower half of the slope, where implies otherwise normal erosion, whether it Jijia or its tributaries. Dynamics, morphology and thickness of colluvial are varied in relation to the specific geological substrate, with slope land, vegetation cover, human activities and other factors. Some deluvial fragmented form steps (with rotational movements), others form mounds or waves or mixed form. Bodies slided occupies the triangular or cvasicircular shape, and linear or slightly sinusoidal surfaces (isolated cases), the latter being own to deluvial plastic or streams, formed under conditions of temporary water excess (Posea, 2005). Field observations indicate that deluvial thickness varies, usually between 2 and 5 to 7 m and by entwining of deployed bodies were formed extensive aprons, sometimes by thousands of sqm (eg: Miletin, Sitna, Başeu basins) (Bacauanu, 1968). Fig. 6. Current geomorphological processes in the bank of Prut belonging Iasi county (Photo source: F. Vartolomei) 96
Many reactivation are regressive propagate (delapsive type) and are caused by disruption of riverbanks or bank-slope, a situation that appears to generalize across the Prut valley. In torrents cases, deluvial so reactivated manage to temporarily obstruct bed of collector river, as often happened on the Prut tributary valleys in Iasi county. Although relatively rare, we meet shallow lenticular, elongated, lobed or circular landslides. Some are grouped by area of several hundred of sqm in Bahlueţ, Volovăţ and Sitna basin. Picture of mass movements enriched with subsidence and collapse, processes that rarely intermingle. They employ both deposits in relative balance and layers of rocks in place. The most common situations characterized steep banks and slopes strongly sloping hillsides (Prut, especially between Corogea river and the confluence with Jijia) and flysch cliffs of detachment sliding, not exempt any edges of terraces (Fig. 6). Individualization badlands sites show current morphodynamics paroxysm relief under the joint action of a plurality of processes favored by many factors. "Bad lands" are exemplified in many parts of the Prut basin, especially the Moldavian Plain (Fig. 7). Fig. 7. Surface erosion processes and their effects in Prut basin (Photo source: F. Vartolomei) 97
Landform visible changes from one month to another and especially in early summer, when mass movements appear to be the maximum dynamic, more relief microforms, whether it is increasing or even disappear more and more from alluvial material composition roofs is moved Prut river bed. In a word, it is pronounced reactivation process that imparts a highly accelerated evolution of the slope. 5. CONCLUSIONS Lately syntheses and generalizations conclude that meadow steps with altitude below 5 m are Holocene age and terraces between 5 and 40 m are upper-pleistocene age. Floodplains were formed in the Holocene age, but have been remarkable changes in the contemporary period, when the degradation is very obvious. The dimensions of terraces will vary depending on the size of the river, having width of a few tens or hundreds of meters, in tributarries cases and up to 5-10 km and even more in the middle and lower Prut basin. Increasing silt downstream thickness from 2-5 m to 30-40 m in the Prut floodplain. REFERENCES Băcăuanu, V., 1961, Observaţii geomorfologice asupra văii Prutului dintre Rădăuţi şi Stânca- Ştefăneşti, Analele Şt. ale Univ. Al. I. Cuza din Iaşi, seria II, Ştiinţe Naturale, Fascicola 2, p. 433-440, Iaşi; Băcăuanu, V., 1968, Câmpia Moldovei-studiu de geomorfologie, Editura Academiei, p. 163, p. 176-177, Bucureşti; Băcăuanu, V., 1973, Evoluţia văilor din Podişul Moldovenesc, Realizări în Geografia României- Culegere de studii, p. 227-235, Bucureşti; Băcăuanu, V., Barbu, N., Pantazică, Maria, Ungureanu, Al., Chirac, D., 1980, Podişul Moldovei - Natură, om, economie, Editura Ştiinţifică şi Enciclopedică, p. 98-129, Bucureşti; Bogdan, Octavia, 2007, Caracteristicile precipitaţiilor din sectorul vestic al văii Prutului (România), Studii şi cercetări de Geografie, Editura Academiei Române, tom. LI-LII/2004-2005, p. 13-28, Bucureşti; Muşinschi, V., 2000, Terasele Prutului, Revista Geografică, Studii şi cercetări de Geografie, Editura Academiei Române, tom. LI-LII/2004-2005, Bucureşti; Posea, Gr, Cruceru, N., 2005, Geomorfologia generală, Editura Fundaţiei România de Mâine, p. 154-189, Bucureşti; Tufescu, V., 1946, Confluenţele şi formarea luncilor Siretului şi Prutului, Revista Geografică, ICGR III,, Bucureşti, p. 76-98; Vartolomei, F., 2003, Graniţele pe ape ale României, Revista Forţelor Terestre, Nr. 1 din 2003, pag. 66-71, Bucureşti; * * Bază de date în format GIS, www.geo-spatial.org; * * www.gisdevelopment.net/glossary. * * http://www.eea.europa.eu/ 98