Workshop PWO 06

Date: August 29 September 1, 2004
Place: Varna (Bulgaria)
Convenors and authors: Ilia Bruchev , Georgi Frangov , Nikolai Dobrev,
Plamen Ivanov , Antonio Lakov

The field workshop aims to demonstrate natural (seismicity, erosion,landslides and rockfalls) and human-induced hazards endangering important natural and archeological monuments.Covering central position in the Balkan Peninsula and being a crossroad between three continents, the territory of Bulgaria is marked by vestiges and monuments from ancient time till nowadays. The oldest gold treasure(~ 4000 years B.C.) was found in the city of Varna. The main goal of the field trip is to present some selected monuments of culture from different historical periods; the geological conditions in which they are located; the consequences caused on them by damaging geological processes (landslides, rockfalls, earthquakes, weathering) and the measures taken to prevent some damages later on.The Bulgarian State was established in 681 in Northeast Bulgaria, and three (Pliska, Preslav and Veliko Tarnovo) amongst its five capitals  are situated there. Historical, cultural and natural monuments included in the World Heritage List of UNESCO are situated there, and namely, the Madara horseman, the Ivanovo rock-hewn churches, the Sveshtari Thracian tumuli, and the natural reserve - Srebarna Lake. Many unique geological and historical places of interest are also present, such as Pobitite kamani(the Upright stones) near Varna, the rock scarps in Madara and Shoumen plateaus, Veliko Tarnovo and its beautiful landscapes and mediaeval historical monuments, the Transfiguration Monastery in the valley of Yantra River,the city of Rousse and the problems with the loess collapsibility, etc.Most of the monuments are placed in complex geological conditions. They have suffered of collapses and deformations at different levels by geological hazardous processes. Some of them are in critical conditions.
After continuous discussions, some measures have been applied to reduce the geological risks for the most valuable monuments During the field trip, discussion on Mitigation of Natural and Man-made Hazard and Risk for Historical and Cultural Heritage will be done. The main aim of the discussion is to share information, experience and ideas on the possibilities for conservation and stabilization of the affected sites.

Madara Horseman
The historical complex Madara is situated in the eastern periphery of the village Madara, 70 km west of Varna and 10 km to the SSW of the first Bulgarian capital - Pliska. The historical bas-relief is situated in a place with many other historical monuments included in the Madara archeological and historical reserve.The Caves of Madara were inhabited from the Neolithic time. The Big Cave was considered sacred and used mainly for the spiritual rituals. It was also known as the Cave of the Nymphs of Nature, Water and Forest. In different periods of time, the Little Cave was inhabited by Thracians,Romans, Slavs and Bulgarians.  The Madara Fortress (6th Century A.D.-14th Century A.D.) indicates the important strategic position of the Madara Plateau from the Roman period of the Justinianus I (527-565) up to the Bulgarian Middle Age (1386). Relics of a Proto-Bulgarian Pagan sanctuary(9th century A.D.) and an Orthodox monastery (9th century A.D.- 10th century A.D.) are found at the foot of the Plateau.The Madara Horseman is a magnificent bas-relief cut into a vertical rock surface at a height of 23 m. The bas-relief depicts the royal lion hunt, and is unique in its kind in Europe. The horseman represents the Bulgarian ruler (Kan), and the inscriptions (in Greek) from the beginning of the 8th to the 9th century around the bas-relief are the first short chronology of the Bulgarian state formation.The bas-relief and the text are of great importance for the Bulgarian culture and history. The monument is included in the List  of the World Cultural Heritage Sites of UNESCO in 1979.

The Madara area is a plateau at a height of c. 400 m a.s.l. It is situated within the northern flank of the Provadia Syncline with layers dipping at 5 to 7 to SE.The rock massif consists of two complexes: Lower Cretaceous marly complex(Hauterivian) and  Upper Cretaceous limy-sandy complex (Cenomanian) age. A borehole located into the bas-relief profile in the plateau, found 137.50 m of the Cenomanian rock complex showing several lithologic varieties.The bas-relief has been carved out of yellowish limy sandstones found between 17 and 100 m. Between the Hauterivian and Cenomanian complexes a layer of yellow plastic silty clay 0.4 - 6.5 m thick has been discovered. The underground water table was found at the depth of 110 m from the plateau surface.The morphology of the slope in the NW periphery of the Madara Plateau is determined by a two layer model.The rock wall is almost vertical built by the limy-sandy complex. Downwards the slope covers marlstones by deluvial deposits dipping at angles from 10 to 20.The peripheral zone of the Madara Plateau developed a specific structure of rock slices released from the edge.The slices or blocks show thickness from 1 to 3 m in average.The Madara Horseman cross section developed six such slices separated from the plateau. The first three of them can be found now as very low steps in the lowest section of the wall being relics of old frontal blocks disintegrated in their towering heads. The bas-relief is carried by the fourth rock slice. Formation of two or three new slices about 3 m wide can be detected behind the furthermost edge of the plateau by cracks.

Rock slices separated from the plateau Fissures that develop during gravitational extension in this slope were described with "X" (followed by numerals). The two uppermost and most extended fissures (X1 and X2) separate Slices 5 and 6 into the plateau, respectively.Slice 4 carries the Madara Horseman. It is cut by three basic cracks threatening the compactness of the bas-relief. Crack No. 1 forms the northern boundary of Slice 4. It is almost vertical from the top down to the level of the bas-relief where turns to S and disappears behind the tail of the dog. Crack No.2 cuts the horse in two parts and reaches the depth of the fifth slice from the surface. Other four to five different cracks are detected between Slice 3 and the base of the massif. The cracks join together to form a single one near the head of Slice 3, extended by 20 and 30 mm under the bas-relief and by 10 and 12 mm in it.Crack No.3 is the most dangerous for the monument. It is extended to 20 mm out of the rock wall. Near the bas-relief and above, it becomes wavy,and disappears about 6 to 7 m above the monument. Thus, the crack is going to separate a prismatic piece of rock between No.3 and No.2 cracks.The stability of the rock mass is a function of rock properties and jointing, and also affected by seismic events, erosional processes, climatic conditions and human activities.Crack gauges TM-71 applied to many rock stability projects successfully were installed here in 1990. According to the seismotectonic prognostication of NE Bulgaria, the Madara Plateau and its wider region is characteristic of high potential seismicity where earthquakes with magnitudes more than 5 could be generated. The most significant influences were noticed during the Vrancea earthquake on 30 May 1990 when stone blocks fell down from the scarp endangering the hu-man lives at the foot of the plateau. During the strong Turkish earthquake on 17 July 1999 large displacements between rock lamellae were established by the high precise monitoring system.The field trip will enable the participants to observe the consequences of rockfalls issued of earthquakes and erosion processes, and to discuss possible measures for conservation of this unique monument.

Other sites

Mediaeval cave churches along the river Rousenski Lom
Thracian tomb (tumulus) at Sveshtari, Sboryanovo cult complex
Ruins of the first Bulgarian capital Pliska (681 - 893)
Here the Bulgarian king Boris and his noblemen were baptized in 864 AD
"Pobitite Kamani" (upright stones) near Varna
A unique natural feature formed in the Eocene sea and further modelled by erosion
Mediaeval cave churches (Aladzha Monastery) near Varna
threatened by earthquakes,rockfall,landslides,erosion
and human activities

Geological Institute of the Bulgarian Academy of Sciences
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