ISSN 1314-3379

ГЕОДИНАМИЧНИ ПРОЦЕСИ ПО БЪЛГАРСКОТО ЧЕРНОМОРСКО КРАЙБРЕЖИЕ

Веселин Д. Пейчев , Димитър П. Димитров , Магдалена В. Пейчева

Резюме . Разгледани са срутищата и свлачищата по Българското черноморско крайбрежие , причините за възникването им , фактори за активизиране , признаци за наличие и мерки за укрепване и стабилизиране на склоновете . Ключови думи : Българското черноморско крайбрежие , срутища и свлачища

Landslides along the Bulgarian coast amount to 79 and cover 12% of its length (about 45 km) on an area of 37 km 2. They are concentrated mainly in the coastal area of the Danube plain (86% of the length and 97% of the area of all landslides). This is favored by the slope of the beaches on the Moesian platform which is 3-4° to north-east of the Black Sea trough and the vertical movements of the crust rise at a rate 2-4 mm / yr forming high and steep slopes, that develop landslides. Of the endogenous earth processes the most important are earthquakes for the occurrence of landslides. According to historical evidence in the I st century AD a big earthquake happened which was followed by a landslide at c. Chirakman near , where the city Bisone sunk into the Black Sea waters. In 1901 an earthquake with magnitude 7.2 and intensity IX-X degree by Medvedev- Sponheuer-Kárník (MSK) scale with epicenter located 10-15 km east of c. caused great destructions and activated the landslide in Momchil village at 3.5 km west of . After the earthquake in Vrancha, in 1977 (magnitude 7.2 and intensity III-IV degree by MSKscale) Balchik landslides were activated. In 1977 the landslide near Kabakum was associated with a weak earthquake (magnitude 3.2, intensity III degree MSK) (fig. 1, fig. 2).

Fig. 1. Landslide near Kabakum

Fig. 2. Landslide near Kabakum road. 3

ISSN 1314-3379 The main exogenous processes affecting the landslides along the Bulgarian Black Sea coast are abrasion and the impact of surface and groundwater. In recent years the role of technogenic factors has also increased (undermining and overloading of slopes, flooding by water supply and sewage networks, dynamic loads), especially in the urban, industrial, resort and villa areas along the coast. A lot of landslides are located between the Romanian border and c. . There the shore is composed of loess with thickness of up to 20 m, below which lies limestone. Abrasion in the loess has an average rate 30 cm/yr, but in some sectors reaches 1-2 m / yr. The waves undermine the shore and form a cliff and wave-breaking niches which at reaching critical condition collapse. Since loess is a loose rock and only 1% of its particle size composition is >0.1 mm, the collapsed material is washed out to a great depth as a result of which the abrasive process is resumed. Typical translational landslides are developed in the limestone that forms the coast between c.Shabla and c.Kaliakra. These are the landslides Yaylata and Taukliman located at 1-2 km south of the village of . Yaylata landslide is 2 km long and up to 250m maximum wide. Three differently shaped and sized landslide steps are formed on its area with the largest being the lowest one, 1.3 km long and 200 m wide. At 200 m south of Yaylata is located Taukliman landslide, 3.2 km long and 500 m wide. Eight landslide steps of different heights are observed there. The slip surface is cracked. Continuous strip of old and contemporary landslides extends between Kavarna and Varna in the Sarmatian limestone, clay, marl and sandstone. The landslides start immediately west of the port of Kavarna town. The larger ones are Kalkantepe (1.8 km long, 700 m wide and 0.8 km 2 area) and Ikantalaka (length 1.4 km, width 1.1 km and an area of 1 km 2) (fig.3).

Fig. 3. Landslip Ikantalaka.

East of Balchik a large landslide is manifested in Tuzla area where in its lowest part is located the salt lake Balchishka Tuzla, sizes 500 x 220 m. The landslide Sarmatian limestone blocks have slipped along the underlying marl and clay. In Balchik landslide amphitheater most pronounced are three east-west oriented translational landslides: Dzhinibayr at an altitude of 123 m, Susambayr - 85 m, Sivritepe - 50 m. They still continue moving with speed of a few inches / year. In Balchik, the limestone blocks of Karvunska formation slip on the clay of Topolska formation. The circus-shaped Momchil landslide is located 35 km west of Balchik. It occurred after the 4

ISSN 1314-3379 earthquake in 1901, 1 km long and 600 m wide. Several landslide flows are formed in its body. When in September 1966, fell 42% of the yearly rainfall in the region, the base of the landslide body, composed of marl, sandy clays and clays passed into plastic state and started moving quickly under the weight of the upper part of the landslide, which was built of rough debris. Transverse cracks 2-2.5 m deep were formed. As the sea continuously washes out the tongue of the landslide, the process is resumed. West of Momchil landslide is located Karamanli landslide, 1.2 km long and 500 m wide. Between and Varna is situated the broadest landslide complex on our Black Sea coast. It covers the eastern slope of Franga Plateau and its width is increased north-south from 250 m to 4600 m. Sarmatian limestone lies on clays and clayey marls and slips on them. This is favored by the fault zones in the area and underground aquifers. Large landslides occurred in 1971 at Kranevo vineyards (fig.4) where 24 villas were destroyed and in 1997 at Kabakum site, south of the International House of Journalists and Pchelina (fig.5, fig.6).

Fig. 4. Landslide near Kranevo

Fig. 5. Landslide Pchelina from south 5

ISSN 1314-3379

Fig. 6. Landslide Pchelina from north.

On the eastern slope of Avren Plateau are located landslides mainly of translational type: Galata, Patrapantepe, Adabahcha, Sakama Gully, St. Marina, Rodni Balkani, Obruka, Kilik and Romantika. They stretch with a break of 12 km between c.Galata and Kamchia River and cover an area of 2.8 km 2. They are developed in sandstones, sands and marls. The landslides along the Balkan Mountains (Stara Planina) coast , Sota and Emine are small with total area 1.4 km 2 and total length of 5 km. Built of Senonian-Emine flysch, mainly siltstone and marl. Along the south Bulgarian Black Sea coast there are landslides at c. Lahna and living quarter. At c. Lahna, Sarmatian limestone and sandy clays slip on Pliocene clays. The landslide at Sarafovo is 3 km long and 280 m wide. It is of a circus-shaped type with three step-like strips separated from one another by swampy depressions. The slip surface is located in the Pliocene clays over which slip clays, limestone and sandstone seams. Landslide process is activated by abrasion which reaches rate of 0.5 - 2.5 m / yr. The active Sarafovo landslide has destroyed hundreds of acres of farmland and threatened the road Varna - until the construction of a protective dike in 2002. On Table 1 is shown data about the biggest contemporary active landslides along the Bulgarian Black Sea coast.

Table 1.Active landslides along the Bulgarian Black Sea coast over the last 60 years

№ Location Year Length Width Depth of slip Area Volume m m surface - m 10 3 m2 10 6 m3 1936, 40, 3000 280 15 840 3.6

1 Sarafovo 79,97

2 Balchik, Moskva Str. 1952, 73,85 200 135 21 27 0.6

3 Zlatni pyasatsi - 1963, 77 1500 400 25 600 15 Kranevo 4 Panorama 1967, 71, 1200 175 25 210 2.8 75, 76, 97

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ISSN 1314-3379 5 Kranevo 1971, 75, 81 800 225 35 180 5

6 1972, 80, 84 550 220 24 121 2.8

7 Balchik, near the 1973, 75, 200 110 24 22 0.5 Palace 79, 86, 90

8 Rusalka 1977, 90 3500 275 40 963 20

9 Yaylata 1977 1300 200 70 260 9

10 Ikantalak 1979 250 240 15 60 0.9 11 Kranevo, 1979, 64, 230 310 30 71 2.1 Lighthouse Ekrene 2012

12 Galata 1984, 89 200 150 25 30 0.8

13 Varna, 1997 65 150 4 10 0.05 bus stop Pisatel 14 Balchik 1997 650 650 13 420 5 Ovcharovski beach

15 Kabakum 1997 400 250 14 100 1.4

References Dimitrov D. 2010. Geology and Non-traditional resources of the Black Sea. LAP (Lambert Academic Publishing AG). ISBN 978-3-8383-8639-3. 244 p. Marinski J., Ed. 1998. Protection and long-term stabilization of the slopes of the Black Sea coast. , BAS. 198 p. Peychev, V., D. Dimitrov. 2012. Oceanology.Varna. Ongyl. ISBN 978-954-8279-82-6. 490 p.

За контакти : проф . д.г.н. Веселин Пейчев [email protected]

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