Student: Tihomir Chergov
Course: Geology/Geochemistry Natural Science Lab
Instructor: Andrea Koschinsky-Fritsche
Geology and Geochemistry Report: Sofia
Brief Introduction to Bulgaria’s Geography:
Bulgaria consists of three classical regions: Thrace, Moesia and Macedonia. The southwest
of Bulgaria is mountainous, containing the highest point in the Balkan Peninsula – the peak
Musala (2925 meters). The Balkan mountain range runs west-east through the middle of
the country, north of the famous Rose valley. Plains and hill country are found in the
southeast, along the Black Sea in the east, and along Bulgaria’s main river, the Danube in
the north.
The Bulgarian climate is temperate, with cold, damp winters and hot, dry summers.
Topographic map of Bulgaria
Brief Overview of Sofia:
Sofia, the capital of Bulgaria since 1878, is situated in the southeastern part of the Sofia
plain. It is strategically situated in the middle of the Balkan peninsula. Very few capitals
in Europa have the distinctive features of Sofia – average above sea-level height of 550m,
availability of mineral springs with medicinal properties of water, relatively small
distance to the capitals of the other Balkan countries. Sofia is also the economic,
industrial and infrastructural centre of Bulgaria.
Geological Development:
In geological respect, the Sofia Kettle represents graben (a vertically sank earth
crust block) filled with sediments from the Neogene. The sink took place in the
form of faults (cracks in the earth crust), which main orientation was North -west –
South-east. The graben is filled not only with sediments (by-products of
precipitation on the slopes of the surrounding mountains and the valleys of the
rivers from that time) but also with materials deposited in the then existing local
basins of lake-marsh origin.
Geological map of Sofia
There are three stages of sedimentation. During the first of them (about 8 -9 million
years ago) the surface water streams and rivers accumulated in the North-Eastern
part of the kettle layers of clay and sand with total girth of up to 400 tones. It is
supposed that those materials were deposited during conditions of drier and colder
climate in comparison with the rocks that are deposited above them. Nowadays
these rocks are not disclosed on the surface and are known only from geological
probes.
7 million years ago, an activation of the movements of the earth crust began to take
place. It lead to the formation of new cracks in the earth crust, accompanied by
lifting of the surrounding mountains and relative falling and spreading of the Sofia
graben. As a result from these processes, a barrier was formed and it obstructed the
flowing of the rivers. This is the reason for the formation of marshes in the whole
northern and middle part of contemporary Sofia plain. The second and most lasting
stage of sedimentation began. On top of the river alluviums from gravels, sands and
sandy clays, horizontally oriented layers of clays with marsh origin, got deposited.
Towards the end of this stage, in the north-western part of the kettle there were
conditions for turning the marsh-peat into coal. Thus, the lignite coals, which are
found nowadays in the region of the village Balsha, were formed. At some places,
the coal layers are replaced by black and less frequently gray clay. The total girth of
the sediments, deposited during this period, is 48-132 meters.
The continuous sink of the earth crust resulted in the formation of a wide and deep
fresh-water lake basin, which, about 6 million years ago, encompassed the southern
part of what is nowadays the Sofia Kettle. Only isolated lifted sections stayed like
islands in the basin. In its deepest parts, clays got deposited, and in its peripheral
parts – sands and gravels. Their total girth was 100-400 meters. Gradually, almost
the whole lake got filled with precipitations and its area drastically shrank. In the
southern part of the basin, primarily river sands and sandy clays got deposited,
whereas in the central part distinct marshes with rich vegetation were formed. The
lake environment was most persistent in the north-western part of the basin. The last
remainder of the lake gradually got filled with precipitations, the marshes got dry
and slowly disappeared. Afterwards, the bottom of the whole kettle was carved out
by rivers, which accumulated river alluviums of girth up to 200 meters, covering all
the previously deposited sediments.
During the third stage of sedimentation ( 5 million years ago) intensive movements
of the earth crust began to take place. They slowly formed the Sofia Kettle in the
way we know it today. Deposited river (alluvial) and inclined (delluvial –
prolluvial) sediments with middle weight of 30-35 tones. On some faults, these
movements have not ceased even today, evidence for which is the considerable
seismic activity of the region.
Relief
The relief of the earth surface, on which Sofia is situated,
stands for its great diversity. The above sea level height
varies from about 500 meters at the town of Novi Iskar up
to 2290 meters at Black Peak. The segmentation of the
relief in Sofia plain is not that significant, which is the
reason for the availability of convenient terrains for
building purposes outside the valuable for agricultural use
lands.
The relief, upon which the area of Sofia is situated, can
be divided into the following geo-morphological units:
the kettle bottom, mountain feet, slopes and slope steps of
the adjoining mountainous systems, ridge backs and
valley bottoms.
Visualization of
Sofia’s relief
The bottom of the cattle is occupied by the vast Sofia
plain. About 8 million years ago, it was a lake, which
flew away north-westward in the direction of
contemporary Morava river towards the former Panonian
sea. About 1 million years ago, the flow-away channel in
the north-west got covered with alluviums. The movements of the earth crust in
combination with a number of other processes are the reason for the lake water to
make its way through the Lom sea basin of that time. This process took place
through the carving of the waters into the abandoned since older geological eras
river bed in the region of Kurilo neighborhood in the town of Novi Iskar. The
erosive carving of this river bed speeded up the drying of the Sofia Lake. The
flowing out of the lake took place in several stages. Between these stages the area of
the lake constantly lowered. The stages can be traced out on the old topographic
maps, on which one can distinguish three terrace levels with different relative hei ght
along the destination ranging from Lozenetz to Malashevtzi neighborhoods. The
highest lake terrace is known as the Lozenetz terrace. This terrace level is nowadays
represented by different spots in the area between the villages Ivanovo and
Simeonovo. Exactly this terrace shows the location of the periphery of the bottom of
the former lake, when its water reached its maximum height. The relative height of
this lake terrace is about 40-50 meters above the present valley bottom of the river
Iskar. After the maximal Lozenetz stage, the level of the lake water started
lowering. Fragments of the modified coastline of the former lake can be observed
near Lozenetz, Big and Small Konyovitza, and the Slatina redoubt. About 500
thousand years ago, the lowering of the lake water level ceased and, as a result, for a
continuous period of time (about 300 thousand years), a new underwater lake terrace
got shaped. Nowadays, this terrace shows the location of the borders of the former
lake bottom. The terrace is situated at a height of 18 up to 24 meters above the
present day river bed of the Iskar river. This terrace level is revealed best near the
Slatina neighborhood, hence being named Slatina level. Upon it a considerable part
of the city area is built up. At many places the Slatina terrace level is separated from
the following lower level by a steep swath. This means that the flowing away of the
lake water after the second stage, took place quickly until it got stable about 150
thousand years ago at its ultimate stage. This last stage shows the small size of the
former lake. The Slatina Lake Terrace is located at a height of 12 to 15 meters
above the present river bed of the Iskar river and it is really vast.
The last stage of the flowing out of the lake waters took place 12-18 thousand years
ago. Of the lowest parts of the former lake bottom today remained small -sized
marshes along the river valley of Iskar river and Lesnovska river between
Kumaritza and Ravno pole. As a result of the drying and the accompanying change
in the erosive basis, the rivers that flowed into it, carved into the lake deposits at a
distance of 3 to 5 meters, thus modeling the so-called inlet terraces which
accumulate subsoil water.
The mountain feet strip is situated at the periphery of the Sofia plain, on its borders
with the mountains Lozen, Vitosha, Lulin and Stara planina. It is located at the
height belt between 700 and 900 meters and the slope of its relief is between 5 and 8
degrees. This strip is a part of a well-shaped ring of unsoldered or hardly soldered
rock materials of Quaternary age, covering older lake and river-lake deposits. The
main factor for the formation of the mountain feet strip, are the transported and
deposited by rivers alluviums, upon which, later on, the rivers (Kalna, Dragalevska,
Boyanska and so on) carved. Part of the rock composition of the mountain foot are
also materials, deposited by land-slips and land-slides, like those situated around the
Movie-making Centre. Due to the availability of soils with relatively l ow agrotechnical properties, the villages and the numerous monasteries which constituted
the middle age Sredez Holy Forest, were built up on the mountain foot.
The Vitosha step is a part of the mountain foot. It represents a natural continuation
of Lozen mountain, and it is closely related to Vitosha. This step has a hilly relief
and is carved in by the deep valleys of the rivers Bistriza, Jeleznishka, Leva and
Vedena.
Vitosha is a mountain which towers imposingly above the city of Sofia. Its area is
267 squared kilometers, with its length being about twenty kilometers and its width
varying from ten to nineteen kilometers.
A photo of Vitosha
The mountain has a relatively big average above sea level height of 1394 meters.
Vitosha has nine peaks with height above 2000 meters and 14 peaks with height
above 1500 meters. This is a premise for very diverse environmental conditions,
which change very quickly on the way from the mountain foot to the high peaks.
The steep northern slopes, the poorly expressed slope steps and the evened out
ridge, give the mountain a pronounced alpine appearance. The mountain is young in
age. Its rising above 2000 meters is a result from the repeatedly displayed vertical
movements of the earth crust in the last 67 million years. Although, from the
position of the Sofia plain, the mountain looks like a volcano, it has no such origin.
The rock from which it is composed, is syenite. The big rocky heaps of spherically
even blocks in the area of the Golden bridges, Shtastlivetza, Cherniy vruh, Bistriza
etc. are remainders of the Ice age.
Lulin is a small mountain with a narrow ridge back and a very steep northern slope
towards the Sofia plain. Its wide mountain foot above the river Bankya and the
surrounding neighborhoods is cut by the carved in it mountainous gorges, which
waters flow into the river Bankya. The mountain is cut off by the Buchinski
passage.
The Lozen mountain has a unique origin. About 10 million years ago, an old lake
existed on its place. In its water, alluviums mixed with vegetation were deposited,
known today as the Chukursky coal basin. The mountain is low – its highest peak is
Popov dyal (1226 meters). Notwithstanding its low above sea level height, the
mountain offers a good view towards the mountains Rila, Stara planina and Vitosha.
Its ridge is narrow, and between the rising cone-shaped peaks saddles with meadow
vegetation were formed.
Plana mountain resembles in its shape Vitosha, but its above sea level height is
abount 1000 meters lower. Its relief is distinct for its wide and even ridge, and very
steep slopes, which go down toward the valley of Iskar river. On this level the
different hamlets of the Plana village are built up. Between Plana and Lozen, there
is the beautiful gorge of Pancharevo with its typical forms such as river rapids,
mountain walls, land-slips, land-slides and the meander Urvich, which used to be a
fortress of the Bulgarian king Ivan Shishman.
Environmental Issues:
The main environmental problem of Sofia is the pollution of the air which is a result
mainly of the high concentration of industries inside and around the city. Of about a
thousand industrial enterprises, two hundred emit considerable amount of polluters.
Moreover, 60% of the industrial enterprises are situated inside neigh borhoods of
Sofia. The main air polluter is the Kremikovtzi combine – it is accountable for about
72 % of the whole air pollution in Sofia.
However, nowadays the level of pollution has decreased significantly compared
with that before 1989. Nevertheless, this fact is not due to anti-pollution measures
rather than considerable shrinkage of Bulgarian industry after the fall of the
Communist regime. And since the increasing amount of foreign investment in
Bulgarian economy lately brings about prognoses for a new industrial growth, it is
very probable that the old levels of pollution may soon be reached again. Another
factor that may significantly contribute to that process is the very rapidly increasing
concentration of motor vehicles in Sofia – a problem faced by most big cities around
the world.
The forthcoming accession of Bulgaria into the European Union which is dated for
2006, is expected to reinforce the ecological measures against pollution. Bulgaria
should meet the anti-pollution criteria of the EU countries as well as adopt modern
techniques for managing this adverse problem.
References:
-Sofia municipality official web site. Retrieved: March 20, 2005 from:
http://www.sofia.bg/history.asp?lines=104&nxt=1&update=all
-Wikpedia – the free encyclopedia. Retrieved: March 20, 2005 from:
http://en.wikipedia.org/wiki/Bulgaria#Geography
-Geology Faculty at Sofia University. Retrieved: March 20, 2005 from:
http://geology.hit.bg/framd.html