Geography KEYWORDS : Landslide processes, Destruction, Geomorphological danger LANDSLIDE PROCESSES IN THE SHUMEN PLATEAU REGION ABSTRACT

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1 LANDSLIDE PROCESSES IN THE SHUMEN PLATEAU REGION Geography KEYWORDS : Landslide processes, Destruction, Geomorphological danger Dimitar Todorov ladev Konstantin Preslavsky University of Shumen, Faculty of Sciences, Department of Geography, Bulgaria ABSTRACT The paper deals with the results of a complex research on the reasons for landslide activity ant present day manifestation of landslide in Shumen plateau. Special attention has been paid to the main factors leading to landslide processes the tectonics, litologo-stratigraphic peculiarities and physico-mechanical properties of the rock complexes and the soils, the underground waters, climate, vegetation and anthropogenic influences. A detailed morphographic and morphological characteristics of the landslides in the region of the roads between the villages of Kochovo and Lozevo and between Shumen and Divdyadovo has been offered as well as the possible means for prevention and control of landslide activities. INTRODUCTION The territory of Bulgaria is characterized with varied geologo-geomorphological, soil, climatic, hydrological and plant conditions, which under certain circumstances could cause processes and phenomena unfavourable and risky for people. Some of the most significant catastrophic phenomena that have a negative effect on the environment, infrastructure and people s possessions are the landslides. The importance of the landslides research is proved by the fact that in the period of they are second in frequency after the floods (National Program for Disaster Defence). Most of the big landslides are registered with the Ministry of Regional Development and Planning (more precisely with the geodefence societies in Pernik, Pleven and Varna), but there are some which are not registered. There are many landslides which are not monitored, there is no information about their condition and assessment about their imminent activity, what the material losses could be and whether the life of the population and the farm animals could be endangered. The Bulgarian Earth Observation Office, which incorporates the Global Environment and Safety Monitoring, has very scant information on landslides, based mainly on media coverage but not preventive information on landslide danger. The Map of landslides in Bulgaria (Scale 1: ) made in 2006, is being constantly updated. According to the MRDP there were 1625 known landslides at the beginning of 2013 (13 of them most active) with a total area of decares. Geodefence data show that there are 917 landslides in settlements, resorts and villa zones, 504 of them active, 208 potentially active and 205 stabilized. According to Geodefence Ltd in Varna there are 265 landslide areas in the regions of Varna, Dobrich, Shumen Burgas, Yambol and Sliven (77 of them have been fortified), with 28 active landslides. There are only 4 landslides for the region of Shumen Plateau (all of them in Divdyadovo) in this list, all of them non-active. 2 of them (registered in 2005 and 2011) are connected with water pipes passing near them, 1 (registered in 2001) is near the city dump. Only 1 of the landslides (registered in 1996), between Shumen and Divdyadovo, was investigated in One can find discrepancies in the information on landslides coming from Geological dangers and risks section of the Institute of Geology at the Bulgarian Academy of Sciences and the Geodefence subdivisions. The reason for this is that geodefence societies do not do a preliminary assessment of the potential places of landslides but just register already active ones. MORPHOHYDROGRAPHIC NOTES ON THE RESEARCHED RE- GION Shumen Plateau is situated in Northeast Bulgaria. It is in the shape of an irregular quadrangle, segmented by bay-like river valleys. The plateau borders to the north the valleys of the rivers Pakosha, Strazhka and Chairdere; to the west the valleys of the rivers Pakosha and Vrana; to the south the continuation of the valley of the river Vrana, the valley of the rivers Ticha and Kamchia; to the east the Shumen-Smyadovo substructural lowlands. The Fiseka height (500.5 m), situated in the north-west, is often included as part of the plateau. Shumen plateau is about 12 km long in west-east direction; its length changes in south-north direction from 7-8 кm in its southernmost part, to 9-10 кm in the central part, to a bit more to the north and to about 20 km in the northernmost part. In north-south direction in its width varies between 15 and 17 km. The total area of the plateau is km2. At the Terziyata col Shumen plateau divides into two parts: eastern wide and western narrower. Its highest point is Turnovtabiya peak (501.9 m.) and its lowest point with an altitude of about 200 m is situated in the vicinity of Kortalaka (north-west of Kazaltepe peak m). The mean altitude of the plateau is 350 m. From geomorphological point of view the relief of Shumen plateau could be divided unto three parts ridge, slopes and foot. The ridge is undulating with a karsts relief with predominating slanting slopes and segmentation. The slopes in the periphery of the plateau are with an incline of 15-30, in some places under the rock wreaths the slope is vertical and even overhanging. The vertical and horizontal segmentation in these areas is the greatest. A constant surface flow can only be found in some peripheral parts of the plateau. The rivers and brooks (draining just 10% of the whole area) form a radial river web. They are short with a predominant underground (karsts) feed, tributaries to the rivers Golyama Kamchiyaand Provadyiska. In the foot parts of the plateau the rivers are the most powerful and form incut valleys. The outflowing underground waters wet the rock layers and under certain conditions they can turn into gliding surfaces and a factor for forming landslides. A karsts basin of 8.5 кm2 has been formed due to the underground karsts relief of the central part of the plateau. The permanent component is prevalent in the river flow (over 80%) and the underground karsts waters feed the ground basins of the border descents. Crevice waters are typical of the western parts of the plateau (water feed of the rivers Novoselska, Kochovska and Osmarska) lying in sandy and marl limestone, limy sandstones and chalky limestone. The mean annual underground water flow in Shumen plateau has been computed to 4.75 litres/sec./кm2 (Geography of Bulgaria, 1997). A BRIEF GEOLOGICAL, SOIL AND PLANT CHARACTERIS- TICS IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH 85

2 The geology (Fig.1), soil surface and vegetation are the object of analysis because they are important factors of landslide processes. Shumen plateau is a part of the South-Misian periplatform region. The upper Cretaceous layer forms Shumen synclinal and geologically the relief is inverse. The southern leg of Shumen synclinal is complicated because of the faults near the village of Kochovo. Shumen synclinal has a few secondary undulations - the synclinal of Ildaztabiya, the synclinal of Cherencha, the anticlinal of Lozevo, the anticlinal south of Turnovtabiya (501.9) and the synclinal of Divdyadovo (Karagyuleva, 1971). Fig.1. Geological Map of Shumen Plateau Research Paper the beech (twice as less), oak and Turkey oak. Approximately hectares of the upper part of the plateau have been turned into a nature park and 90.1% of the whole territory of the park is forested. The rest of the territory is glades, roads and clearings. Coniferous forests cover about 16% of the vegetation and are mainly black pine trees. Deciduous tall forests occupy about 15%. They are mainly beech trees as well some mixed forests of Turkey oak, oak, hornbeam, ash and acacia. The forest vegetation helps the stabilizing of the slopes thus preventing them from sliding. ACRIVE LANDSLIDES ON THE SLOPES OF SHUMEN PLA- TEAU The landslide areas are slopes and batters which can move or could be put into unstable condition under the influence of a number of natural and artificial phenomena. Geodefence societies in Bulgaria glean information only about the landslides in settlements, resorts and the villa zone territories. There is no monitoring of the forests and the roads of the third and fourth network. Because of some regulations the landslides in the inner part of Shumen plateau are not the object of research and monitoring. Different destructive processes take place in Shumen plateau. Geochemical migration is characteristic of the soils and rocks in the karsts territories. The carbonate rocks and the almost dense forestation and grass covering make it difficult for the water erosion of the upper part of the plateau. The risk of water erosion is high for the southern and south-eastern slopes and for some of the incut valleys and steep slopes. The rain waters and those from the melting snow are very easily absorbed in depth, thus feeding the underground karsts basins. The landslides along the slopes of Shumen plateau get active usually in spring (April-May) or autumn (November). At this time of year the underground waters are the highest, but in some years (like the present 2014) because of continuous rainfalls the underground waters stay high even in summer. In the wooded parts of the plateau one could find Cretaceous limestone and marls, along the southeastern and southwestern slopes - Cretaceous sandstone and marls and in a few places in the southern and northern part Paleogenic marls, clay sands and limestone (Cheshitev, Nedyalkova, 1995). Faults of different size have been discerned, some of proved during terrain investigations (Vladev, 2000). The vertical movements of the earth crust of Shumen plateau at present times vary from +0.8 tо +1.1 mm.per year (Totomano et al. 1978). Landslide activity along the eastern slope of Shumen plsteau between Shumen and Divdyadovo The Geological Danger in Bulgaria map in scale 1: (BAS, 1994) shows an almost continual line of a landslide region along the eastern, south-eastern and southern part of Shumen plateau, parts of which become active periodically. Te terrain research showed no continual line. There is a big active landslide along the eastern slope of the plateau with a four-lane highway passing along it (photo 1). There are no registered strong earthquakes with an epicenter at Shumen plateau but the plateau is close to the highly seismic Gorna Oryahovitza and Shabla regions and the less dangerous Provadiya region (Geological danger in Bulgaria, 1994). Baring rocks, karsts, hydroclimatic conditions and the specific vegetation on the plateau led to the appearance of damp, clayey and shallow carbonate soils as well as regular decarbonated rendsins. There are also patches of anthropogenated soils in some places (Geography of Bulgaria, 1997). According to the Classification Scheme of the types of forest habitats (1983) Shumen plateau is part of the Misian forest-vegetation region the lower plain-hilly and hilly-foothill belt of the oak forests. Offshoot forests are the most widely spread forests on the plateau. The main tree type is the hornbeam, followed by Photo 1 General view of the landslide between km 6.55 and 7.0 on the road between Shumen - Divdyadovo. In the foreground the terraced slope south of the landslide tongue. 86 IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH

3 This landslide (with an area of about 1 кm2) has been known to the local population for a very long time but was only registered by Geodefence in The slope, 700 m long with a subsidence of almost 300 m, descends from west-northwest to east-southeast. The landslide is 400 m wide at the lower break of the slope. Two landslide zones, going to old gullies now covered by the road, are discernable within it. According to the incline the landslide refers to the steep ones (15-45 ; Fig.2) and by the depth of sliding it belongs to the deep landslides. The active part of the landslide body is m long. The soil-rock material moves at the speed of 0.05 to 5 mm/24h. Photos 2-3. Deformations and cracks in the asphalt road between Shumen and Divdyadovopassing through the landslide. About 400 m of the road are the most risky ones. Besides the steep incline of the slope and the road passing by it, a significant role in activating the landslide plays the increased level of the underground waters. They wet the gliding surface of the landslide. The drainage, built at the end of the 20th century manage to take to the surface some of the underground waters, but because of blocked sewage it is difficult to take them to the dam which is 500 m away. Since 2007 the Municipality of Shumen has been trying to raise several million levs for fortifying the landslide because they cannot be covered by the budget. There are repair works every year but the problem could only be solved when the landslide is stopped and fortified. Landslide activity along the western slope of Shumen plateau, above the road from the village of Kochovo to the villages of Novosel and Lozevo. Fig. 2. Map of the real inclines in the area of the landslide, 5th km region Shumen Divdadovo There are several platforms marking the bigger slides and the lowest is above the lower break of the slope. The highway passes (at an altitude of 225 m) by the rear side of the second platform which is 62 m wide (Photo 2). The front part of the landslide tongue is 28 m from the highway. The evidence that the landslide is active can be seen in the deformations in the road and the cracks in the asphalt (9-10 m long, gm deep and cm wide Photo 2-3). Deformations and terrain cave-ins can also be seen in the rear part of the landslide tongue just over the road. The cracks here are cm wide and over 1 m deep (Photo 4). These peculiarities are a proof that it is only a matter of time for part of the road to slide down. What is more, this already happened in the not so distant past (in 1996). In the road caves in again about six thousand people, who live in Divdyadovo, will be cut off from Shumen. A landslide complex of several big ones and a large number of smaller detrusive landslides can be found along the western slope of Shumen plateau, west and northwest of Tarnovtabiya peak (501,9 m). Approximately along the direction of the motorway (SHU-2005) is the western boundary of Shumen Plateau Nature Park. The instability of the slope can be seen from as far away as Tarnovtabiya peak (501.9 m), where there are caved in, unnaturally bent or uprooted hornbeam and beech trees (Photo 5). The whole area affected by the landslides is about 3-4 кm2, and the depth of the sliding surface is from 4 to 6 m. The speed of movement of the rock-soil materials is from 0.05 до 20 mm/24h. According to the incline (15-45 ) the slides could be referred to the group of the steep ones (Fig. 3). Subsidence (steepness) of the slope here is among the biggest on the plateau. Only m from the western edge of the plateau the difference in altitude is already 100 m. The road between the villages of Kochovo and Lozevo has been closed for some years now because of the active landslides in the section southwest of Zanoga locality through Akkaya locality up to junction (km 12.86) for the villages of Novosel and Lozevo. This section is about 5 km long. From north to south there is a series of embankments under road level and separate slides above it. Fig.3. Map of real inclines in the landslide area on the road between the villages of Kochovo and Lozevo IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH 87

4 Research Paper The southernmost part of the front (20 m wide) consists only of pelite rocks (Photo 8) and the rest of the landslide is characterized with chaotically mixed clays, pieces of marl and chalk limestone (Photo 9). The surface of the body and the front of the landslide is littered with erosion furrows, crevices, cave-ins, pieces of broken and displaced rock blocks. The trees give the effect of a drunk forest, characteristic for landslide regions (Photos 8, 9). The front part of the first big landslide has reached and covered part of the road (at an altitude of 314 m). It is a mix of soil, marl, clays and chalk limestone. The landslide cut, marking the upper part of the landslide body is about 15 m high. Photo 8. Erosion furrows and crevices in the front of the landslide Photo 6. Elements of the landslide: front part, body, landslide cut (in the background) Photo 9. Chaotic mixture of subsident, broken and displaced rock formations North of the big landslide has been built a fountain, which drains some of the underground waters feeding the gliding surface of the landslide. 60 m uphill there is a smaller landslide whose upper part is limited by a cut 4 m high. Most of the rock materials that have moved here (at an altitude of 362 m) have covered more than half of the road. (Photo 10). Then follows a series of some more local landslides. The slope, both above and below the road, remains unstable. Vehicle traffic causes breaks and cave-ins in some parts of the asphalt cover (Photo 11). Photo 7. The landslide overcomes the road, despite the concrete props The landslide is 150 m long and about 130 m wide (Photo 6). There has been an attempt to stop it with closely placed concrete blocks but with a very little effect. (Photos 6, 7). There are sections with different rock formations in the landslide tongue IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH

5 Photo 10. Front of an active new landslide Photo 11. Condition of the road below the landslide Local slope landslides become active from time to time in the Kyoshkovete nature park and its environs. These happen mainly in the Zandanski, Chanadzhishki, Sarhoshcheshmenski gullies. Crawling slopes that move at a speed of up to 0.01 mm/24 h. can also be found in the upper part of the water collecting zone of the Poroina River and its tributaries, which drain this part of the plateau. There have been cases of typical landslides as well. The last time something like this happened was on May 19, 2014, when the earth mass of the activated landslide moved about 40 m and reached some building in Krusha street. According to Civil Protection and Water Supply Service in Shumen the reason for the landslide, besides the rain, was a breakdown in an old watersupply network feeding the local brewery. Fortification works went on for two months. CONCLUSIONS 1. The main factors for the landslides happening in Shumen plateau are: the physico-mechanical peculiarities of the rocks and the soils, the steep slopes, the specific hydroclimatic conditions and the human activity. There is also a non-permanent anthropogenic pressure on the plateau from Shumen and other settlements on the region. 2. The landslide processes in Shumen plateau are active and it is scientifically ungrounded to expect that they will cease soon. In the last 5-6 years when this research took place there was a tendency of increased periods of activity connected with continuous rainfalls. This means that the rainfalls should be studied and analyzed as a prognostic element for the landslides. 3. The landslides in the region of Shumen plateau cause serious problems to the population and the infrastructure which means that in the shortest possible time there should begin a systematic investigation (monitoring, including geodesic surveys) of each of them. It is necessary to use innovative methods of monitoring the behaviour of the landslide processes, analyzing the results, prognostics and carrying out fortifying activities in the bigger landslides. * With the decision of the Council of Ministers (May 2014) the Interdepartmental Commission of Disasters and Accidents sanctioned a project ( financed with 3.75 mln levs) for the fortification of the landslide and the road between Shumen and Divdyadovo. The plan is to move two sections of about 350 metres of the road, where the landslide is the most active and build two bridges, 40 m long, scraping the base of the road, thus ensuring the draining of the surface and underground waters in the direction of Shumen dam. 1.Vladev, D. 2000, Structural-Geomorphological Research of Shumen Plateau Region Based on Space Photos, In: Scientific-Technological Transfer, 3-4 X 2000, Geography of Bulgaria, M. Drinov Acad. Publishing House, The Geological Danger in Bulgaria, Iliya Bruchev (editor), Explanatory Text to Map with a Scale of 1: , CGMR, BAS Publishing House, State Gazette, issue 68 Regulation No. 12/ on Designing geo defended buildings in landslide regions. 5. Karagyuleva, Yu. 1971, Northern Belt of the Balkan Mountains, In: The Tectonics of the Northern Balkan Mountains, S. BAS, Map of the Landslides in Bulgaria (Scale 1: ), Classification Scheme of the Types of Forest Plant Habitats in Bulgaria National Program of Disaster Defence, List of the Landslides in Bulgaria Geodefence Ltd Varna, Totomanov, I, B. Vrablyanski, М. Mladenovski Research and Mapping of the Present Vertical Movements of the Earth Crust in Bulgaria, Problems of Geography, book Cheshitev, G., L. Nedyalkova, 1995, Explanatory Note to the Geological Map of Bulgaria with a Scale of 1: , Shumen branch, CGMR, Geology and Geophysics JSC, 49 REFERENCE 1.Vladev, D. 2000, Structural-Geomorphological Research of Shumen Plateau Region Based on Space Photos, In: Scientific-Technological Transfer, 3-4 X 2000, Geography of Bulgaria, M. Drinov Acad. Publishing House, The Geological Danger in Bulgaria, Iliya Bruchev (editor), Explanatory Text to Map with a Scale of 1: , CGMR, BAS Publishing House, State Gazette, issue 68 Regulation No. 12/ on Designing geo defended buildings in landslide regions. 5. Karagyuleva, Yu. 1971, Northern Belt of the Balkan Mountains, In: The Tectonics of the Northern Balkan Mountains, S. BAS, Map of the Landslides in Bulgaria (Scale 1: ), Classification Scheme of the Types of Forest Plant Habitats in Bulgaria National Program of Disaster Defence, List of the Landslides in Bulgaria Geodefence Ltd Varna, Totomanov, I, B. Vrablyanski, М. Mladenovski Research and Mapping of the Present Vertical Movements of the Earth Crust in Bulgaria, Problems of Geography, book Cheshitev, G., L. Nedyalkova, 1995, Explanatory Note to the Geological Map of Bulgaria with a Scale of 1: , Shumen branch, CGMR, Geology and Geophysics JSC, 49 IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH 89