Natural Park “Blue Stones” is part of the Balkan Mountain chain of “Balkanides” formed during Cenozoic, Pyrenean and Savski stages. Present-day land relief dates back to Neogene – Quaternary period and is the result of the action of endogenous and exogenous land forming forces and processes, as well of the vertical crustal movements. The last major crustal movement of decrease was registered in 1905. At the same place , as a result of active erosion and water forces, a huge landslide was caused in 1912 – 1913.
The rock phenomenon “Blue Stones” was formed as a result of massive erosion and denudation processes which took thousands of years. One can observe interesting rock formations of sandstone, limestone , coarse-grained granite and other. In the area of “Assenivets” dam lake cretaceous sandstones, alevrits, marl, lava rocks, black sicily and others are very likely to see. Aluvial formations have been discovered along the valley of Sotirska River ; on the southern slopes of Mount Motrun – slope embankments built of sandstone ;and Mount Balgarka stands on coarse-grained granite. This diverse structure of the mountain has allowed the erosion forces to form the mighty shoulders of the Blue Rocks – labyrinth of peaks, huge sheer precipices, caves, valleys.Because of that, the Blue Rocks have been defined as “A wonder of Nature” – the travellers have given them the name “The Alps of Sliven” because of their resemblance with the famous mountain range.
The rivers in the park are typically mountainous with lots of rapids, pools and waterfalls, which makes them spectacular.The glens in the western and eastern regions are wider longer and woody, without many slopes, and in the central region – narrow, steep and short.Asenovka river with its main tributaries Magareshka and Davidova rivers is the longest one in the region , also its forestland is one of the most spacious.The deepest river is Ablanovska river, and ones with the most interesting streams are Novoselska, Kushbunarska , Sotirska and Dalboki Dol rivers.
The climate in the region is temperate continental with predominant air masses from the Atlantic ocean and commonly spotted far-away continental and Mediterranean incursions.Black Sea influences the climate as well.The absolute temperatures are approximately from +41 C to – 20 C. At high-altitude regions in the summer the weather is cool , and in the lower parts – dry and hot. In winter, there is often snow in Daula und Kushbunar. Usually it is not until 2th November before it begins to snow and by the beginning of March it has already started to melt.Maximum amount of rainfall can be measured in May, and minimum – in August.
North and northwest winds are typical of the region, as well the wind “bora”, which is often mentioned as “the wind of Sliven”. In the summer , a wind called “vechernik” is often formed at the foot of the mountain slopes and river valleys. It changes its direction – during the day it blows to the mountains, and at night – to the valley.The main types of soil are cinnamon forest ones and brown earths.There are also intrazonal soils, such as humus-carbonate, talus, Lithosols.
Bedrocks of cinnamon forest soils are represented by conglomerates, sandstones, clays, tuffs and others.They occupy altitudes on up to 700-800 metres above the sea level.On places lik this, oak and hornbeam vegetation is typically to spot.Brown earths, whose bedrocks are sandstone, limestone, dolomite, brechko conglomerates, are located between 800 and 100 above the sea level.
The park is also famous for its variety of minerals , in proof of which a lot of excavation work has been done in the area of “Zmeevi dupki”.In ancient days, big amounts of iron- and manganese ore, as well as coal, have been extracted.