The western portion is lower and more dissected; in the east it becomes regular but somewhat higher, better resembling a plateau. Bulgarians name local areas within it, but they do not name the region as a whole.
It is a fertile area with undulating hills and is the granary of the country.
The southern edge of the Danubian plateau blends into the foothills of the Stara Planina, the Bulgarian extension of the Carpathian Mountains.
The Carpathians resemble a reversed S as they run eastward from Czechoslovakia across the northern portion of Romania, swinging southward to the middle of that country, where they run westward and cross Romania as the Transylvanian Alps. At a famous gorge of the Danube River known as the Iron Gate, which forms part of the Romania-Yugoslavia border, the Carpathians again sweep eastward, becoming Bulgaria"s Stara Planina range.
Considered in its local context, the Stara Planina originates at the Timok Valley in Yugoslavia, continues southeastward as it becomes the northern boundary of the Sofia Basin, and then turns more directly eastward to terminate at Cape Emine on the Black Sea. It is some 370 miles in length, and some twelve to thirty miles in width. It retains its height well into the central part of the country, where Botev Peak, its highest point, rises to about 7,800 feet. The range is still apparent until its rocky cliffs fall into the Black Sea. Over most of its length, its ridge is the divide between drainage to the Danube River and to the Aegean Sea. In the east small areas drain directly to the Black Sea.
Sometimes considered a part of the foothills of the Stara Planina, but separated from the main range by a long geological trench that contains the Valley of Roses, is the Sredna Gora (Middle Forest). The Sredna Gora is a ridge running almost precisely east to west, about 100 miles long.
Its elevations run to only a little more than 5,000 feet, but it is narrow and achieves an impression of greater height.
The southern slopes of the Stara Planina and the Sredna Gora give way to the Thracian Plain. The plain is roughly triangular in shape, originating at a point east of the mountains that ring the Sofia Basin and broadening as it proceeds eastward to the Black Sea. It encompa.s.ses the Maritsa River basin and the lowlands that extend from it to the Black Sea. As is the case with the Danubian plateau, a great deal of this area is not a plain in strict terms. Most of its terrain is moderate enough to allow cultivation, but there are variations greater than those of a typical plain.
[Ill.u.s.tration: _Figure 2. Topography of Bulgaria_]
The Rodopi occupies the area between the Thracian Plain and the Greek border. This range is commonly described as including the Rila mountain range south of Sophia and the Pirin range in the southwestern corner of the country. As such, the Rodopi is the most outstanding topographic feature, not only of the country, but also of the entire Balkan Peninsula. The Rila contains Mount Musala--called Mount Stalin for a few years--whose 9,500-foot peak is the highest in the Balkans. About a dozen other peaks in the Rila are over 9,000 feet. They feature a few bare rocks and remote lakes above the tree line, but the lower peaks are covered with Alpine meadows, and the general aspect of the range is one of green beauty.
The Vitosha range is an outlier of the Rila. A symmetrical, 7,500-foot high, isolated peak in the range is a landmark on the outskirts of Sofia. Snow covers its conical summit most of the year, and its steep sides are forested.
The Pirin is characterized by rocky peaks and stony slopes. An impression of the landscape is provided by a local legend, which says that when the earth was being created G.o.d was flying over the peninsula with a bag of huge boulders. The rocks were too heavy for the bag, and it broke over southwestern Bulgaria.
Some Bulgarian geographers refer to the western Rodopi and the Pirin as the Thracian-Macedonian ma.s.sif. In this context, the Rodopi includes only the mountains south of the Maritsa River basin. There is some basis for such a division. The Rila is largely volcanic in origin. The Pirin was formed at a different time by fracturing of the earth"s crust. The uplands east of the Maritsa River are not of the same stature as the major ranges.
Sizable areas in the western and central Stara Planina and smaller areas in the Pirin and in Dobrudzha have extensive layers of limestone. There are some 2,000 caves in these deposits. The public has become more interested in the caves during the past three or four decades, but only about 400 of them have been completely explored and charted.
To the east of the higher Rodopi and east of the Maritsa River are the Sakar and Strandzha mountains. They extend the length of the Rodopi along the Turkish border to the Black Sea but are themselves comparatively insignificant. At one point they have a spot elevation of about 2,800 feet, but they rarely exceed 1,500 feet elsewhere.
Formation of the Balkan landma.s.ses involved a number of earth crust foldings and volcanic actions that either dammed rivers or forced them into new courses. The flat basins that occur throughout the country were created when river waters receded from the temporary lakes that existed while the rivers were cutting their new channels. The largest of these is the Sofia Basin, which includes the city and the area about fifteen miles wide and sixty miles long to its northwest and southeast.
Other valleys between the Stara Planina and the Sredna Gora ranges contain a series of smaller basins, and similar ones occur at intervals in the valleys of a number of the larger rivers.
Drainage
From a drainage standpoint, the country is divided into two nearly equal parts. The slightly larger one drains to the Black Sea, the other to the Aegean. The northern watershed of the Stara Planina, all of the Danubian plateau, and the thirty to fifty miles inland from the coastline drain to the Black Sea. The Thracian Plain and most of the higher lands of the south and southwest drain to the Aegean Sea. Although only the Danube is navigable, many of the other rivers and streams have a high potential for the production of hydroelectric power and are sources of irrigation water. Many are already being exploited.
Insignificant when compared with the watersheds that drain to the seas, about 125 square miles of the country drain into a few small salt lakes that have no outflowing water. The largest such lake has a surface area of 2.5 square miles.
By far the greater part of the country that drains to the Black Sea does so through the Danube. Most of its major tributaries in the country (from west to east, the Ogosta, Iskur, Vit, Osum, Yantra, and Lom) carry more water than do the combination of the Provadiyska, Kamchiya, Fakiyska, and Veleka rivers, all of which flow directly into the Black Sea. Of the Danube"s Bulgarian tributaries, all but the Iskur rise in the Stara Planina. The Iskur rises in the Rila and flows northward through a narrow basin. Territory not far from the river on both sides of it drains in the opposite direction, to the south. The Iskur pa.s.ses through Sofia"s eastern suburbs and cuts a valley through the Stara Planina on its way to join the Danube.
The Iskur and the other of the Danube"s north-flowing tributaries have cut deep valleys through the Danubian plateau. The eastern banks tend to rise sharply from the rivers; the western parts of the valleys may have broad fields with alluvial soils. The peculiar, though consistent, pattern is caused by forces resulting from the earth"s rotation; these forces give the water a motion that tends to undercut the right banks of the streams. Some of these rivers are sizable streams, but the Danube gets only a little more than 4 percent of its total volume from its Bulgarian tributaries. As it flows along the northern border, the Danube averages one to 1.5 miles in width. Its highest water levels are usually reached during June floods, and in normal seasons it is frozen over for about forty days.
Several major rivers flow directly to the Aegean Sea, although the Maritsa with its tributaries is by far the largest. The Maritsa drains all of the western Thracian Plain, all of the Sredna Gora, the southern slopes of the Stara Planina, and the northern slopes of the eastern Rodopi. Other than the Maritsa, the Struma in the west and the Mesta (which separates the Pirin from the main Rodopi ranges) are the two largest of the rivers that rise in Bulgaria and flow to the Aegean. Most of these streams fall swiftly from the mountains and have cut deep, scenic gorges. The Struma and Mesta reach the sea through Greece. The Maritsa forms most of the Greek-Turkish border after it leaves Bulgaria.
About 3,750 square miles of agricultural land have access to irrigation waters. Dams provide the water for about one-half of the acreage; diversions from rivers and streams serve about one-third; and water pumped from the ground and from streams accounts for the remainder.
Of the dams, ninety-two are termed large state dams. Their combined capacity is three times that of some 2,000 smaller dams. The sources of four large rivers--the Maritsa, Iskur, Mesta, and Rilska (a major tributary of the Struma)--are within a few miles of each other in the high Rila. Water from the upper courses of these and several other streams supplies the Sofia area with both water and electricity, and they have a potential for further development. There are major dams on the Tundzha, Iskur, Rositsa, and Struma rivers. The Danube is too ma.s.sive a stream to harness, and damming the Maritsa along most of its course would flood too much valuable land. The rivers flowing north across the Danubian plateau also tend to be overly difficult to use in the areas where they are most needed.
The Vucha River, flowing from the Rodopi into the Maritsa River, is often used to ill.u.s.trate how rivers have been effectively harnessed to provide a variety of benefits. Its cascade system of hydroelectric development employs six dams having the capacity to generate over 600,000 kilowatts of electricity. The water they back up serves the munic.i.p.al water systems in Plovdiv and a number of other towns in its vicinity, and the dams provide irrigation water for nearly 250,000 acres of cropland. The reservoirs themselves are being developed as recreational areas and mountain resorts.
Where a stream is difficult to dam or to divert, water is pumped from it. This has been feasible only since about 1950, when low-cost diesel engines and sufficient hydroelectric power became available from newly constructed dams on other streams. About eighty-five huge pumping stations have been set up along the Danube River, which furnishes about three-quarters of the water acquired by this method; and in 1970 there were about 1,200 lesser stations operating on smaller streams, most of them on the Thracian Plain.
Climate
For so small an area, the climate varies widely and is unusually complex. Depending upon the depth to which they study the area, climatologists list six or more climatic subzones. The country lies on the line of transition between the strongly contrasting Eastern European continental and the Mediterranean climatic zones, and its mountains and valleys are local factors that act as barriers or channels to the air ma.s.ses, contributing to sharp contrasts in weather over relatively short distances. The Black Sea, although too small to be a primary influence over much of the country"s weather, also affects the immediate area along its coastline.
In general, continental systems prevail in the north. They are characterized by hot summers, cold winters, and precipitation well distributed throughout the year, a major portion of it in early summer thunderstorms. The Mediterranean climate that is influential most of the time in the south has mild, damp winters but hot, dry, rain-free summers. The Stara Planina marks the lower limits of the area in which continental air ma.s.ses circulate freely in typical circ.u.mstances. In the area between them and the Danube River there is an extension of the climate that is common to east-central Europe and adjoining regions of the Soviet Union.
In the same fashion, the Rodopi marks the northern limits of domination by Mediterranean weather systems. The southern slopes of these mountains are sufficiently mild to merit the region"s being called the Green Greece or Bulgarian California.
The area in between, which includes the Thracian Plain, is influenced by both types of climate, but more of the time by continental systems. The result is a plains climate resembling that of the corn belt in the United States, which is characterized by long summers and high humidity.
The climate is generally more severe than that of Spain and the portions of Italy, France, and Soviet Georgia that are in the same lat.i.tude.
Because it is a transitional area and the Mediterranean systems may prevail for most of some seasons or retreat from the scene altogether in other seasons, average temperatures and precipitation are erratic and may vary widely from year to year.
Precipitation over the country averages about twenty-five inches a year and, when it is distributed normally throughout the seasons, it is satisfactory for most agricultural crops. Dobrudzha, in the northeast, the Black Sea coastal area, and parts of the Thracian Plain usually receive less than twenty inches. The remainder of the Thracian Plain and the Danubian plateau get less than the country average. Higher elevations are the most generously watered, in some places receiving forty inches or more.
Although a low figure of 7.6 inches was recorded in Dobrudzha for one year and the normal precipitation is marginal, both Dobrudzha and the Danubian plateau are in the continental climate zone and usually receive most of their rainfall during crop-growing seasons. The Thracian Plain, however, has frequent seasons when it is under Mediterranean influences and, when this is the case, it may experience prolonged summer droughts.
Irrigation is, therefore, necessary for dependable agricultural production.
A few sheltered pockets in the higher mountains may remain covered with snow all year, and much of the other higher land remains white well into springtime. Lower elevations are snow covered an average of twenty-five to thirty days a year. Average cloudiness is about 55 percent, and average relative humidity is as high as 70 to 75 percent.
The many valley basins throughout the uplands frequently have temperature inversions resulting in stagnant air. The Sofia area, for example, is occasionally troubled by smog. The city"s elevation of about 1,800 feet, however, tends to moderate summer temperatures and to relieve the oppressive quality of the high humidity. It is also sheltered from the northern European winds by the mountains that ring the basin. Its temperatures in January average about 29F, and in August they average about 70F. Its rainfall is near the country average, and the overall result of the several contributing features is a rather unexpectedly pleasant climate.
The climate of the coast is moderated by the Black Sea, but there are many windy days and violent local storms during the winter. The area along the Danube River experiences bitterly cold winters, and sheltered valleys opening to the south along the Greek and Turkish borders may, in contrast, be as mild as though they were on the Mediterranean or Aegean coasts. The so-called Black Wind, a local phenomenon similar to the African sirocco, consists of hard-blowing, hot, very dry air and wreaks havoc on crops. It gets its name from the quant.i.ties of dust it carries, which often darken the skies.
Regions in the Rodopi and the higher elevations around Sofia feature sun and snow in a pleasant combination for about four months a year. Several places have good and reasonably dependable skiing and are being developed into holiday resorts.
Soils
Fine, dark chernozem (black earth) soils, rich in loess and humus, occur over a considerable portion of the northern Danubian plateau. They are fertile, easy to work, and compare with the best soils in Europe. Away from the river, approaching the mountains, there is a broader area that is basically similar, but the subsoils are more porous and have allowed the humus and loess to leach downward from the surface. The resulting gray soil no longer rates among the finest, but it yields good crops in some areas and, where it is less satisfactory, the land is forested.
The Thracian Plain has comparatively little of the finest soils, but it has much soil that is more than adequate to produce reasonably good crops. The best on the plain is locally called _smolnitsa_. It is basically a chernozem, but it is less fully matured and coa.r.s.er than the darker variety along the Danube. The plain also features fairly extensive areas of good brown and brown forest soils. Meadow soils occur in large areas in the vicinity of Plovdiv. Some are irrigated and cultivated.
Meadow and layered podzol (gray forest) soils occur in most of the higher elevations throughout the country. Intermediate elevations usually have brown forest soils, some of which are excellent. The Maritsa and Tundzha and the major rivers that flow into the Danube have wide valleys with alluvial soils. They may be coa.r.s.e, but most of them are fertile, drain well, and are extensively cultivated.
Vegetation
Both the natural vegetation and the cultivated crops that have replaced it on all areas that could be put to agricultural use reflect the transitional climate of the country. North of the Stara Planina the original flora was a continuation of that on the Russian steppe. The steppe influence was greatest in the east, giving way to deciduous forests farther to the west.
Lands south of the mountains, sheltered from the colder extremes of the continental weather systems, have been able to support plant life that could not exist on the steppe. Areas along the Black Sea coast and in valleys of the Rodopi that open to the south experience further moderation. Many Mediterranean and subtropical species have existed in them naturally, and others introduced by man have thrived.
What remains of the original vegetation on the Danubian plateau is found mainly along the river, where the land has been difficult to cultivate.
It includes brush gra.s.s, reeds, and licorice. The last two have commercial value. Most of the original lowland deciduous forests have been removed, and grain flourishes on the level expanses where the soils are favorable. Other food and fodder crops are grown to satisfy local requirements. The foothills of the Stara Planina are dotted with orchards; plums are the most prevalent fruit in these northern areas.
The depression, or geological trench, between the Stara Planina and the Sredna Gora ranges, which is at the near center point of the country and contains the upper valleys of the Tundzha, Stryama, and Topolnitsa rivers, is sheltered and very humid and is ideal for the raising of roses. One in particular, Rosa Alba, has become known as Bulgaria"s gold. Its flower is not an especially lovely variety, but it is extremely rich in the rose oil that is the basic fragrance in many perfumes and a flavor in certain liqueurs. Fields of them flourish in the Kazanluk area, the so-called Valley of Roses.
The Thracian Plain, between the Sredna Gora and the Rodopi, originally featured a mixture of midlat.i.tude forest and Mediterranean flora. The forests have been removed from the level lands and have been replaced by a diversification of crops, including truck vegetables, fruit orchards, strawberries, raspberries, vineyards, tobacco, and cotton. The plain also produces a variety of herbs and medicine derivatives. Digitalis is produced from foxgloves; menthol, from peppermint; opium, from a species of poppy; linseed oil, from flaxseed; laxatives, from iris and rhubarb; and castor oil, from the castor bean. All of them are grown on this plain.