Cascade Range

The Cascade Range is a mountain range located in the northwestern portion of the United States and southwestern part of Canada. It is 1,100 km (700 miles) long and extends from south to north through the State of Oregon, Washington, and British Columbia in Canada. With 4,392 m (1,411 ft) of altitude, Mount Rainier is the highest peak of this mountain system, while Mount St. Helens and Mount Hood are active volcanoes. In 1980, Mount St. Helens erupted with extreme violence and it was recorded on film. The Cascade Range gets its name from the abundance of terrace-like waterfalls (cascades) on the Columbia, Fraser, Klamath, and other rivers that cut through the range.

Geologically, the range is composed of Mesozoic crystalline rocks, which was later covered by huge layers of Paleogene and Neocene lavas. However, the Cascade Mountains belong to the Tertiary orogeny of the Cenozoic era, as it was formed and elevated by the collision and subduction of Juan de Fuca tectonic plate against the North American plate, sliding beneath it. Above this strongly dissected volcanic plateau, which is from 1,800 to 2,500 m high, rise isolated cones of volcanoes, such as Mount Baker, Mount Rainier, Mount St. Helens, Mount Hood, and Lassen Peak, with altitudes of 3,000 to 4,000 m and more.

Although most of the volcanoes are extinct, some of them are still active, such as Mount Rainier, Lassen Peak, and Mount St. Helens, which showed their greatest volcanic activity in the late 19th and 20th centuries. Signs of volcanic activities can be seen in mountain slopes, which abound in fumaroles and hot springs. The volcanic peaks are covered with vast snow fields and glaciers. Dark coniferous forests grow on the humid western slopes of the range and pine trees on the dry eastern slopes; above 2,800–3,000 m, the forests give way to subalpine and alpine meadows. There are copper and gold deposits in the mountains. Crater Lake, Mount Rainier, and Lassen Volcanic national parks are located in the Cascade Range.

The Cascade Range extends from Oregon to Canada.

Cenozoic Era

The Cenozoic era is the time span in which we are living now. It began 66 million years ago right after the Mesozoic. This present time era is divided into two periods, the Tertiary and the Quaternary (Anthropogenic). The Tertiary is characterized by the formation of the newest and largest mountain ranges on the planet, which have the highest peaks, such as Himalaya, Andes, and the Rocky Mountain Range. The Quaternary, on the other hand, is marked by the four glaciation ages and the emergence of big carnivores and human beings. This era also contains the top strata (layers) of the Earth's crust.

If the Cenozoic era is divided into two well-defined periods, each one of these periods consists of epochs. Thus, the Tertiary period is further subdivided into the Paleocene, Eocene, Oligocene, Miocene, and Pliocene. It is very important to point out that during the Miocene the Earth's temperature began to drop as large tracts of forests and jungles started to disappear, giving way to the appearance of the plains, savannas, and steppes, with massive proliferation of graminae (grass) and ruminant herbivores, such as bovines (cattle), ovines (sheep), caprines, and deer. Inordinate numbers of grass grazers triggered the proliferation of big cats and other carnivores, and also human beings; the hunters. The appearance of Homo sapiens would take place during the Quaternary, which geologists divided into two epochs: the Pleistocene and the Holocene (present time); during the Pleistocene, the first humans emerged.

General Characteristics

During the Cenozoic era the present distribution of continents and oceans occurred. The very beginning of the era saw the completion of the breakup of the formerly unified southern continental mass, Gondwana, into the separate continental blocks of South America, Africa, the Indian subcontinent, Australia, and Antarctica, divided by the newly formed basins of the Indian Ocean and the southern part of the Atlantic Ocean —a process that had been under way since the Mesozoic. By the middle of the Cenozoic, Eurasia and Africa formed the continental mass of the Old World, joined by the mountain structures of the Mediterranean geosynclinal belt. The collision of tectonic plates brought about the orogenesis (formation of mountains) of most of the highest mountain ranges on Earth today: the Alps, Himalaya, Andes, Rocky, Cascade Range, etc. During the Quaternary, the large plains rich top soil continue to build up, with grass being the most abundant plant on Earth.

At the beginning of the Cenozoic, the large reptiles, which had predominated during the Mesozoic, became extinct and were replaced by mammals that, with birds, constituted the nucleus of the terrestrial vertebrates of the Cenozoic era. On most continents the higher placental mammals became dominant, and only in Australia (which became isolated before these mammals appeared on a large scale) did unique marsupials and, to some extent, monotremes develop. During the early Paleogene, mammals were represented almost exclusively by small primitive forms. By the middle Paleogene almost all the orders existing today had appeared, as well as several groups that subsequently became extinct. A great variety of mammals evolved and thrived.

Formation of Mountains

The formation of mountains is called orogenesis in geology. This long process of mountain building is caused by the horizontal collision of tectonic plates. In other words, when two tectonic plates collide and push against one another, with one edge sliding and crashing beneath the other's; this is called subduction, which is the result of two tectonic plates convergence. There is crumpling of layers of rocks into folds as they rise up, gaining altitude. As a result, large masses of molten rocks and geological materials are uplifted in vertical tectonic movements, whose rate exceeds that of the exogenous process of destruction and removal (erosion) of rock or the process of buildup of sediments (accumulation), which lead to the leveling of the earth’s surface. Orogenesis, or orogeny, is characteristic of active regions of the earth.

When the term “orogeny” was introduced, it had been established that the crumpling of layers of rock into folds led directly to the formation of mountains. One hallmark of orogeny is the formation of orogenic belts, which are elongated areas of deformation that borders continental cratons. Young orogenic belts, in which subduction is still taking place, are characterized by frequent volcanic activity and earthquakes, such as relatively new mountain ranges from the Tertiary period, like the Himalayas, Andes or the Rocky Mountain Range. Older orogenic belts, on the other hand, are typically deeply eroded to expose displaced and deformed strata. These are often highly metamorphosed and intrusive igneous rocks, which are called basoliths (granite and quartz monzonite).

Orogenesis is a geological term introduced by the American geologist G. Gilbert in 1890 to designate mountain building and intense deformation by folding and faulting. Gilbert singled out orogenic movements of the earth’s crust and contrasted them to epeirogenic movements, that is, slow upward and downward movements. The concept of orogeny was further developed by the French geologist G.-E. Haug, who, in 1907, proposed that orogeny be distinguished only within geosynclinal regions. Subsequently, in 1919, the German geologist H. Stille hypothesized that the chief result of orogeny was not the formation of mountains but rather the formation of folds.

Appalachian Mountains

The Appalachian Mountains constitute the oldest mountain system in North America. Lying in the Northeast of the United States, they form a long belt of ranges and ridges, valleys, plateaus and tableland. They extends for 2,600 km (1,616 miles) in a southwest-northeast direction, from 33° north latitude to 49° N lat. The width of this orographic system varies from 300 km (186 miles) to 500 km (311 miles), The main ranges of the Appalachians are the Blue Ridge Mountains, White Mountains, Adirondacks, and Green Mountains. The Appalachian Plateau should also be noted. Their altitude ranges from 1,300 to 1,600 m, with the highest peak being Mount Mitchell, which is 2,037 m (6,683 feet) high.

The rivers of the Appalachians run through deep valleys. The flow is abundant all year round, providing considerable reserves for hydro-power AC generation. The largest rivers are the Connecticut, Hudson, Susquehanna, and Tennessee. They overflow their banks frequently because of melting snow in the spring and heavy rainfall in the summer. The major rivers of the northern Appalachians are navigable. As they fall from the eastern edge of the Piedmont, most of the rivers form rapids and waterfalls (the so-called fall line), which are used in part for power production.

Climate

The weather of the Appalachian Mountains is modified by the influence of the Atlantic Ocean and especially of the warm ocean current of Gulf of Mexico (or America). It is temperate in the north and subtropical in the south. The average temperature in January ranges from - 12°C in the north to 8°C in the south; in July the average ranges from 18°C to 26°C. Annual precipitation is from 1,000 to 1,300 mm. In the winter there are heavy frosts in the upper zone of the mountains, and much snow falls. The valleys are drier and warmer. The summers are humid and cloudy; rainfall is abundant, especially on the western slopes. The clearest and sunniest weather comes at the end of summer and beginning of autumn.

Geological History

The Appalachians were uplifted on the site of a geosynclinal system which developed actively in the Paleozoic era on a late Precambrian folded foundation. Millions of years later, the mountains were leveled during the Jurassic Paleocene period. Mountains reappeared again in the Neocene-Anthropogenic period, when the territory of the modern Appalachians underwent a domed uplift, which resulted in the vigorous breakup of the surface and the formation of the modern terrain. The ranges consist of folded rocks and boulders and are divided by intermontane erosional valleys and basins.

The northern Appalachians border on the Canadian Shield in the northwest, along a huge fault (the Logan line). They lack frontal sag and consist of a narrow belt of lower Paleozoic sedimentary deposits in the northwest and a wider belt of igneous, intrusional magmatites and metamor-phic rock in the southeast. The main tectonic periods for the northern Appalachians were the Taconic (at the end of the Ordovician) and the Acadian (at the end of the Devonian). During the Carboniferous-Permian period intermontane sag developed in the interior, filled mainly with continental deposits, first coal-bearing and then red in color.

During the Anthropogenic period, the northern partion of the Appalachians underwent glaciation, while the southern part remained in a temperate (mild) and humid climate. As a result, forests of broad-leaved and evergreen trees were able to survive there and subsequently to spread over a large part of the Appalachians. By structure and development the Appalachians are divided into the northern and southern regions (with the borderline approximately at the latitude of New York City).

Above, a map of North America showing the Appalachian Mountains.

Ural River

The Ural river is a large stream of fresh water that flows into the Caspian Sea. It is 2,428 km (1,508 miles) in length and it drains an area of 231,000 Km2. It rises in the Uraltau Range of the Southern Ural Mountains, near Mt. Kruglaya, Russia. It first flows in a westward direction, then it turns left at the city of Uralsk, running southward all the way into the Caspian Sea near the city of Gurev.

In its upper course, the Ural is a mountain river. Then it flows through marshy land, after which its valley alternately narrows and broadens to as much as 5 km. Below Verkhneuralsk, it becomes a plain river. At Magnitogorsk and lower, the river is bounded by rocky banks. It was formerly known as the Iaik river before 1775.

The largest tributaries of the Ural are the Sakmara, Irtek, and Chagan on the right, and the Or, Ilek, and Utva on the left. The Olenti, Kaldygaity, and Uil rivers disappear through seepage loss in the Caspian Lowland without reaching the Ural. The Ural freezes over in early November in the upper course, and in late November in the middle and lower courses. The ice breaks up in late March in the lower course and in early April in the upper course. The period of ice drift is short, and ice jams are common. The river is navigable from Uralsk to Gurev.

The Ural river is fed primarily by melting snow. Spring high water takes place from late March to early April in the lower course, and approximately from the middle of the second week of April to June in its upper course. There is minor flooding in the upper course in the summer and fall, and a stable low water level for the remainder of the year. During high water the river overflows its banks in the middle course and exceeds 10 km in width, broadening in the delta to tens of kilometers. The highest water levels occur in late April in the upper course and in early May in the lower course.

Fauna

Ural river fish of commercial importance include sturgeons of the genus Acispenser, especially stellate sturgeon (A stellatus), and also pike perch, herring, European bream, carp, and European catfish. The cities of Verkhneural’sk, Magnitogorsk, Orsk, Novotroitsk, Orenburg, Ural’sk and Gur’ev are situated on the river. The northern mole and the marbled polecat, as well as sand lizards, turtles, and water snakes are also found on the banks of the river.

The Ural river is marked in dark blue. You can also see the Volga, which also flows into the Caspian Sea.

Ural Mountains

The Ural Mountains are the main orographic system of Russia. Running from north to south, they form the natural boundary between Europe and Asia. This mountain range is 2,365 km (1,470 miles) long and it extends from the Arctic to Kazakhstan, east of the Caspian Sea. The highest peak is Mt Narodnaya, which is 1,895 m (6,216 feet) high. The Urals harbor the richest mineral deposits on Earth as it varies in width from 40 km (24.8 miles) to 150 km (93 miles). Meanwhile, the rivers that originate in the Urals drain either into the Arctic Ocean or into the Caspian Sea. The Pechora and Usa on the western slope and the Tobol, Iset, Tura, Lozva, and Severnaia Sosva rivers (all part of the Ob system) on the eastern slope flow into the Arctic, while the Kama River and the Ural River drain into the Caspian Sea.

The Ural Mountains are divided into the Polar, Subpolar, Northern-Central, and Southern Urals. The Polar Urals have average elevations of 1,000 and 1,200 m, rising to 1,499 m on Mount Paier, with ridges having rounded summits. The Subpolar Urals have the highest peaks, Mount Narodnaya (1,895 m) and Mount Karpinskii (1,878 m), and attain a maximum of 150 km. Many of their ranges, among them the Issledovatel’skii and Sablia, have serrated ridges and are deeply and densely dissected by river valleys. Traces of Pleistocene mountain and valley glaciation in the Polar and Subpolar Urals include cirques, U-shaped valleys, and moraines. Modern glaciation is also extensive; the largest of the 143 glaciers that cover the Polar and Subpolar Urals are the IGAN, MGU, and Dolgushin glaciers. Intergelisols are common.

Stretching from north to south, the Northern-Central Urals consist of a series of parallel ranges rising to 1,000–1,200 m and longitudinal depressions. They typically have flat summits, although the upper parts of the higher mountains, notably Tel’posiz (1,617 m) and Konzhakovskii Kamen’ (1,569 m), have a more rugged topography. The greatly worn down Central Urals are the lowest mountains in the system, rising to 994 m on Mount Srednii Baseg. The topography of the Southern Urals is more complex. The numerous ranges of different elevations, trending southwest or north-south, are dissected by deep longitudinal and transverse depressions and valleys. The highest peak is Mount Iamantau (1,640 m).

Karst topography (area of limestone) is extensively developed on the western slope of the Urals and in the Ural Region, particularly in the basin of the Sylva River, a tributary of the Chusovaia. There are many caves (Div’ia, Kungur, Kapova), basins, sinks, and underground streams. The eastern slope has fewer karst formations. Rocky outliers such as the Sem’ Brat’ev, Chertovo Gorodishche, and Kamennye Palatki rise above its flattened or gently rolling surface. Wide foothills, reduced to peneplain, adjoin the Central and Southern Urals on the east, broadening the Southern Urals to 250 km.

Minerals

The Ural region holds many useful and valuable minerals used by the industry. Forty-eight of the 55 most important minerals processed and used in Russia are found in the Urals. The eastern Urals are noted for their deposits of copper pyrite (Gai, Sibai, and Degtiarsk deposits and the Kirovgrad and Krasnoural’sk groups of deposits), skarn-magnetite (deposits of Mount Vysokaia, Mount Blagodat’, and Mount Magnitnaia), titanomagnetite (Kachkanar and Pervoural’sk), nickel ironstone (Orsk-Khalilove group of deposits), and chromite ores (deposits of the Kempirsai massif), mostly confined to the greenstone belt.

The eastern slope also has coal seams (Cheliabinsk coal basin) and placer and native deposits of gold (Kochkar’, Berezovo) and platinum (Isovka). The Severoural’sk Bauxite Region and the vast Bazhenov asbestos deposits are on the eastern slope. On the western slope of the Urals and in the Ural Region there are deposits of hard coal (Pechora and Kizel coal basins), petroleum (Volga-Ural Oil-Gas Region, Orenburg gas condensate deposit), and potassium salts (upper Kama basin). The Urals are especially famous for their precious, semiprecious, and ornamental stones, including emeralds, amethysts, aquamarine, jasper, rhodonite, and malachite. The best jeweler’s diamonds in Russia come from the Urals.

Geological Structure

The Ural Mountains are a late Paleozoic (Hercynian) folded region lying within the Ural-Mongolian folded geosynclinal belt. Deformed and frequently metamorphosed rocks, chiefly Paleozoic, crop out on the surface in the Urals. The region’s sedimentary and volcanic strata are highly folded and broken by fractures, but in general they form north-south bands, which account for the linear and zonal structure of the Urals.

Six geological zones may be distinguished from west to east: (1) the Cis-Ural Foredeep, with a comparatively gentle bedding of sedimentary layers on the west and a more complex bedding on the east; (2) the Western Slope Zone, whose Lower and Middle Paleozoic sedimentary layers are intensively folded and dislocated by thrusts; (3) the Central Ural Uplift, where the more ancient crystalline rocks of the margin of the East European Platform crop out in places among Paleozoic and Upper Precambrian sedimentary strata; (4) the “greenstone belt,” a system of troughs and synclinoria on the eastern slope (of which the largest are the Magnitogorsk and Tagil’ synclinoria), filled chiefly with Middle Paleozoic volcanic strata and marine (often deep-sea) sediments intruded by plutonic igneous rocks (gabbroids, granitoids, and sometimes alkaline intrusives); (5) the Ural-Tobol’ Anticlinorium, with outcrops of more ancient metamorphic rocks and extensively developed granitoids; and (6) the Eastern Ural Synclinorium, in many ways similar to the Tagil’-Magnitogorsk synclinorium.

Using geophysical data, Soviet geologists had established that the first three geological zones rest on an ancient Precambrian basement composed chiefly of metamorphic and magmatic rocks and formed in the course of several epochs of folding. The most ancient rock, believed to be Archean, crops out at the Taratash protrusion on the western slope of the Southern Urals. Pre-Ordovician rocks are unknown in the basement of the synclinoria of the eastern slope of the Urals. It is thought that the thick plates of ultrabasites and gabbroids that crop out in places in the Platinonosnyi and analogous belts serve as the basement of the Paleozoic volcanic strata of the synclinoria. These plates may possibly be broken-off remnants of the ancient sea floor of the Ural geosyncline. Some ancient outcrops in the Ural-Tobol’ Anticlinorium in the east are perhaps Precambrian.

The Paleozoic beds of the western slope of the Urals are composed of limestones, dolomites, and sandstones that were formed for the most part in shallow seas. To the east lies a discontinuous strip of deep-sea continental slope sediments. Still further to the east, on the eastern slope of the Urals, the Paleozoic (Ordovician and Silurian) cross-section begins with altered basaltic volcanites and jaspers that are comparable to the rocks of the present-day ocean floor. Thick spilite-natroliparite strata, also altered and containing deposits of copper pyrite ore, occur in places higher up in the cross section.

Dom Feliciano Belt

The Dom Feliciano belt is a tectonic unit of southern Brazil, Uruguay, and a portion of Argentina's Pampas region. Its internal geological organization shows three narrow and sub-parallel crustal segments: a granite belt at the southeastern end; a central schist belt; and a northwestern foreland belt with volcano sedimentary sequences.

The crystalline rock belt of Dom Feliciano tectonic unit is formed by a series of essentially igneous complexes, of the which the Pelotas batholith in the State of Rio Grande do Sud is the most representative. It was formed in a magmatic arc tectonic environment. The granitoid rocks include a series of deformed calc-alkaline types (tonalite, granodiorite, etc) and many weakly deformed and non-deformed monzogranite. The schist belt include supracrustal rocks in a few discontinuous polydeformed metamorphic complexes.

The crystalline terrains observed in the northern and central-western parts of Dom Feliciano belt are those of Luiz Alves and Rio de la Plata. The Luiz Alves cratonic fragment is a microplate, in which high grade metamorphic rocks are abundant. Meanwhile, the Rio de la Plata craton includes different terrains with ages of formation older than the neo-proterozoic, such as the Tacuarembo-Rivera, Nico Perez, Piedras Altas, and Tandil in the province of Buenos Aires (Argentina). The Tandil terrain constitutes a highly deformed crystalline basement.

Kama River

The Kama River is the main tributary of the Volga, into which it flows from the left side, about 200 km south of Kazan city. It is 1,807 km long and drains a 5,800 km2 basin. The Vyatka is the main tributary of the Kama on the right side, while the Belaya and Vishera River are the largest tributaries on left side. It occupies the 6th place in Europe in length. The total drop of the Kama River from its source to the mouth is 247 meters, while its slope is 0.14 m/km.

The Kama rises in the Udmurt Republic, near Kuliga, in the Kirov region. First, it flows northwest for about 200 kilometers (120 miles). Then it turns near Loyno and flows northeast for another 200 kilometres (120 mi). Next, it winds around at Perm Krai to run in a north-southwest direction, flowing again through the Udmurt Republic and then through the Republic of Tatarstan, where it meets the Volga.

Volga River

The Volga River is one of the longest rivers in the world and the longest in Europe. It is 3,530 km (2,193.4 miles) long, with a basin area of 1,360,000 km2. (before construction of dams, it was 3,690 km long.The Volga rises (originates) in the Valdai Hills, at 228 m above sea level and flows through Russian territory into the Caspian Sea. The mouth lies 28 m below sea level. Approximately 200 tributaries flow into this river. The largest tributaries of the Volga are the Oka, on the right side; the Kama, which flows in from the left side; Sura; Vetluga; and Sviiaga river.

The left tributaries of the Volga are more numerous and deeper than the right. The river system of the basin includes 151,000 waterways (rivers, streams, and temporary waterways) with a combined length of 574,000 km. The basin itself occupies approximately one-third of the Eastern European, stretching from the Valdai and Central Russian hills on the west to the Ural Mountains on the east. At the latitude of Saratov the basin becomes very dry, and the river flows from Kamyshin to the Caspian Sea without any tributaries.

The main, feed section of the Volga’s drainage area, from the sources to the cities of Gorky and Kazan’, is located in the forest zone. The center of the basin up to Kuibyshev and Saratov are in the forest-steppe zone; while the lower part is in the steppe region up to Volgograd as the southernmost part is in the semidesert zone. The Volga is usually divided into three parts: the upper, from the source to the mouth of the Oka; the middle, from the confluence of the Oka to the mouth of the Kama; and the lower, from the confluence of the Kama to the mouth.

The source of the Volga is a spring in the village of Volgo-Verkhov’e in Kalinin Oblast. In its upper reaches, the Valdai Hills, the Volga passes through small lakes—Verkhit, Sterzh, Vselug, Peno, and Volgo. At the outflow of Lake Volgo there was a dam built as early as 1843 (Verkhnevolzhskii Beishlot) to regulate the water flow and to maintain navigable depths during low water.

Between Kalinin and Rybinsk the Volga reservoir (the so-called Moscow Sea) was created, with a dam and hydro-electric power station at Ivan’kov; also on the river are the Uglich reservoir (power station at Uglich) and the Rybinsk reservoir (power station at Rybinsk). In the region of Rybinsk-Iaroslavl’ and below Kostroma the river flows through a narrow valley between steep shores, bisecting the Uglich Danilov and Galich-Chukhlom Hills. Further on the Volga flows along the Unzha and Balakhnin plains. At Gorodets, above Gorky, the Volga is blocked off by the dam of the Gorky hydroelectric power station, forming the Gorky reservoir. The main tributaries of the upper Volga are the Selizharovka, Tvertsa, Mologa, Sheksna, and Unzha.

In its middle portion, below the confluence of the Oka, the Volga becomes even deeper, flowing along the northern edge of the Volga Hills. The right bank of the river is steep, and the left bank low. In 1968 construction was begun at Cheboksar on the Cheboksar Hydroelectric Plant, above whose dam is the Cheboksar reservoir.

In its lower reaches, after the confluence of the Kama, the Volga becomes a mighty river. Here it flows along the Volga Hills. The dam of the V. I. Lenin Volga Hydro-electric Power Plant is constructed near Tol’iatti, above the Samar oxbow, formed by the river as it bends around the Zhiguli Hills; the Kuibyshev reservoir stretches above the dam. The dam of the Saratov hydroelectric plant is located on the river near Balakovo. The lower Volga has relatively small tributaries—the Samara, Bol’shoi Irgiz, and Eruslan. Twenty-one km above Volgograd the Akhtuba (537 km long) branches off to the left and flows parallel to the main course of the river. The broad stretch between the Volga and the Akhtuba, which is crossed by numerous channels as well as bayous, is called the Volga-Akhtuba floodplain; floods on this plain formerly reached 20-30 km. The Twenty-second Congress of the CPSU Volgograd Hydroelectric Power Plant is built on the Volga between the beginning of the Akhtuba and Volgograd.

The Volga delta, which begins where its course separates from the Buzan branch (46 km north of Astrakhan), is one of the largest in the USSR. It has up to 500 branches, channels, and small rivers. The main branches are the Bakhtemir, Kamyziak, Staraia Volga, Bolda, Buzan, and Akhtuba, of which only the Bakhtemir is navigable.

The Volga is fed mainly by snow (60 percent of the annual flow), ground waters (30 percent), and rain (10 percent). In the spring there is flooding (April-June), during summer and winter low water, and in autumn rain floods (October). The annual variation in the level of the river before its regulation reached 11 m at Kalinin, 15-17 m below the mouth of the Kama, and 3 m at Astrakhan. After construction of the reservoirs the Volga’s flow was regulated, and variations in the water level were sharply reduced.

The average annual flow of water at the Verkhnevolzhskii Beishlot is 29 m3/sec, at Kalinin 182, at laroslavl’ 1,110, at Gorky 2,970, at Kuibyshev 7,720, and at Volgograd 8,060 m3/sec. Below Volgograd the river loses about 2 percent of its flow to evaporation. Maximum water flow during the high-water season below the confluence of the Kama formerly reached 67,000 m3/sec, while at Volgograd, as a result of spreading over the floodplain, it did not exceed 52,000 m3/sec. In connection with regulation of the flow, maximum flows at high water have been sharply reduced, while the summer and winter low-water flows have been greatly increased. Over a period of several years the average water balance of the Volga basin before Volgograd has been 662 mm or 900 km3 a year of precipitation, 187 mm or 254 km3 a year of river flow, and 475 mm or 646 km3 a year of evaporation.

Before the creation of reservoirs, the Volga carried to its mouth about 25 million tons of alluvial matter and 40-50 million tons of dissolved minerals annually. The temperature of the water reaches 20-25° C in the middle of the summer (July). The ice in the river near Astrakhan breaks up in mid-March, and in the first half of April the breakup occurs on the upper Volga and below Kamyshin; the rest of the river opens up in mid-April. The upper and middle reaches of the Volga freeze at the end of November, and the lower reaches freeze at the beginning of December; the river is ice-free for about 200 days, 260 days near Astrakhan. The reservoirs have changed the temperature of the river; the duration of ice on the headwaters has been increased, but on the lower reaches it has been decreased.

Historical and economic-geographical sketch. The geographical location of the Volga and its large tributaries gave it great importance even in the eighth century as a commercial route between East and West. Fabrics and metals were brought from the East and traded for furs, wax, and mead from the Slavic lands. Centers such as Itil, Bolgar, Novgorod, Rostov, Suzdal’, and Murom played an important role in trade of the ninth-tenth centuries. Trade began to decline in the llth century; in the 13th century the Mongol Tatar invasion destroyed the economic links, except in the basin of the upper Volga, where Novgorod, Tver’, and the cities of Vladimir-Suzdal’ Rus’ played an active role. In the 14th century the importance of the trade route was renewed, and centers such as Kazan’, Nizhny Novgorod, and Astrakhan grew in importance. Ivan IV the Terrible subdued the Kazan’ and Astrakhan khanates in the middle of the 16th century; this led to the incorporation of the entire Volga river system within the embrace of Russia, facilitating the flourishing of Volga trade in the 17th century. New large cities such as Samara, Saratov, and Tsaritsyn arose, and laroslavl’, Kostroma, and Nizhny Novgorod played large roles. Large caravans of up to 500 ships sailed along the Volga. In the 18th century the main trade route shifted to the west, while the economic development of the lower Volga was checked by sparse population and the incursions of nomads. In the 17th and 18th centuries the Volga basin was the main area for the activities of rebellious peasants and Cossacks during the peasant uprisings led by S. T. Razin and E. I. Pugachev.

In the 19th century the Volga trade route grew considerably after the connection of the Mariinsk River system with the basins of the Volga and Neva (1808); a large river fleet arose (the first steamship in 1820), and a huge army of barge haulers (up to 300,000 men) began to work on the Volga. The river was used for large-scale transport of bread, salt, fish, and later petroleum and cotton. The Nizhegorod market took on great economic significance.

During the Civil War of 1918-20 there were large-scale military actions on the Volga (struggle with the White Czechs and troops of the constituent assembly governments in 1918 and with Kolchak’s and Denikin’s forces in 1919), and it acquired important military-strategic significance. During the years of socialist construction the significance of the Volga route grew in conjunction with the industrialization of the entire country. At the end of the 1930’s the Volga was first used as a source of hydroelectric power. During World War II, the great Battle of Stalingrad took place on the Volga.

In the postwar period the economic role of the Volga increased significantly, especially after the creation of a series of large reservoirs and hydroelectric power plants. After completion of the Volga Kama Cascade Hydroelectric Plant the total output of hydro-electric energy will reach 40-45 billion kvolt/hour a year. The reservoir surface area is about 38,000 km2, the full volume is 288 km3, and the useful volume is 90 km3. The left bank of the Volga, which has 4 million hectares of land suitable for irrigation, is supplied with water from the Kuibyshev and Volgograd reservoirs. Work will be carried out on the flooding of 9 million hectares and the irrigation of 1 million hectares between the Volga and Ural rivers. Construction began in 1971 on the Volga-Ural Canal, 425 km long with a water flow of about 400 m3/sec. The river system includes more than 41,000 km of floatable and about 14,000 km of navigable waterways.

The Volga is linked with the Baltic Sea by the V. I. Lenin Volga-Baltic Waterway and the Vyshnevolotsk and Tikhva systems; with the White Sea by the Sever-Dvina system and the Belomor-Baltic Canal; and with the Black Sea and Sea of Azov by the V. I. Lenin Volga-Don Canal.

Natural Resources and Fish

In the basin of the upper Volga there are large forests, and in the middle and partially in the lower Volga regions there are large areas given over to grain and industrial crops. Viticulture and horticulture are well developed. The Volga-Ural region has rich deposits of oil and gas. Near Solikamsk there are large deposits of potassium salts. In the lower Volga region (Baskunchak and El’ton lakes) there is table salt. About 70 species offish, 40 of which are commercially important (the most important include the Caspian roach, herring, bream, pike perch, sazan, sheatfish, pike, sturgeon, and sterlet) inhabit the Volga.

Nile (River)

The Nile is a large river in northeastern Africa. It is the world's longest stream of fresh water. It is 6,671 km long and drains an area of 2.87 million square km. It rises in the East African Highlands east of Lakes Kivu and Tanganyika and flows into the Mediterranean Sea, forming a delta. The largest tributaries in the upper half of its course are the Bahr el Ghazal (left) and the Aswa, Sobat, Blue Nile, and Atbara (right). Then the Nile receives no tributaries for 3,000 km as it flows through tropical and subtropical semi-deserts. The Nile basin encompasses part or all of Rwanda, Kenya, Tanzania, Uganda, Ethiopia, the Sudan, and Egypt.

The Nile has its source in one of the headstreams of the Kagera River, which flows into Lake Victoria. Issuing from the northern end of Lake Victoria as the Victoria Nile, the river cuts through rocky ridges, and, dropping 670 m, forms numerous rapids and waterfalls. After passing through the Lake Kyoga basin, the river drops 400 m over a comparatively short stretch (the Murchison and other falls) and flows into Lake Mobutu Sese Seko (Lake Albert). Leaving the lake, the river, now called the Albert Nile, receives the Aswa River from the right. It flows on a plateau and then breaks through a rocky barrier at the narrow Nimule Canyon to emerge on the Sudan Plains.

Below Juba the river crosses the swampy Sudd region for 900 km, as far as Malakal; here, throughout most of its course, it is called the Bahr el Jebel. The river channel in this region is clogged by masses of algae and papyrus, called sudd. The river winds sluggishly through the region, losing up to two-thirds of its water by evaporation, by transpiration from the vegetation of the Sudd, and by filling depressions. After receiving the Bahr el Ghazal, the river, now called the White Nile (or Bahr el Abyad), leaves the Sudd and is joined by the Sobat River from the right, which almost doubles its water volume. Below this junction the Nile flows placidly in a broad valley through a semidesert all the way to Khartoum. From the Nimule Canyon to Khartoum, a distance of about 1,800 km, the river drops about 80 m.

At Khartoum the Blue Nile, issuing from Lake Tana, pours its waters into the White Nile. From here to its mouth the river is called simply the Nile River. Between Khartoum and Aswan, a distance of about 1,850 km, the river drops about 290 m. Below the entrance of the Atbara River, the last major tributary, the Nile enters the Nubian Desert, where it crosses low mountain ranges, making a large bend. Outcrops of crystalline rock in one part of the river valley have created the six famous rapids, called cataracts, which hindered navigation before the construction of the Aswan High Dam.

Between Aswan and Cairo (900 km) the drop is slight, and the river flows in a broad valley up to 20–25 km wide. The Nile delta begins 20 km from Cairo. It has an area of 22,000 to 24,000 sq km (according to different sources), with numerous arms and lakes stretching along the coast from Alexandria to Port Said for about 260 km. In the delta the main channel of the Nile divides into nine large branches and many small ones. The principal branches for navigation are the Dumyat (Damietta, eastern) and the Rashid (Rosetta, western), each of which is about 200 km long. Some of the Nile’s waters pass through the Ibrahimiya Canal and the Yusuf branch into Lake Birka Qarun and are to irrigate the Fayyum Oasis. Fresh Nile water is supplied to the Suez Canal region through the Ismailia Canal and to Alexandria and its environs through the Mahmudiya Canal. The lagoons of Lakes Manzilah, Burullus, and Maryut are in the northern part of the delta.

The Nile has a complex regime. In the equatorial part of the river basin there are two periods of maximum precipitation, one in the spring (March to May) and the other in the fall (September to November), causing an increase in the water volume below the Nimule Canyon in the summer and winter. In the Sudan and the Blue Nile basin, the Nile’s second main source of water, rain falls in the summer (June to September). In the Sudan the Nile overflows during the summer as a result of the monsoon rains, but it loses a great deal of water through evaporation so that the Blue Nile is the chief source of water for the Nile, contributing 60–70 percent of its water during the summer. As a result the waters of the Nile rise during the summer and fall in the central and northern Sudan and in Egypt. High water occurs in Lower Egypt between July and October. The average water discharge at Aswan is 2,600 cu m per sec, with a maximum of 15,000 cu m per sec and a minimum of about 500 cu m per sec. During average high water the river rises 6 to 7 m in Egypt. Severe flooding occurred before regulatory structures were built in the Nile Valley. The annual discharge of solid matter at Aswan is 62 million cu m, much of which is deposited as silt on fields, in irrigation canals, and in reservoirs.

The Nile Valley and particularly its delta were one of the centers of ancient civilization. Since ancient times the water resources of the Nile have been used for irrigation, the natural fertilization of fields, fishing, water supply, and navigation. The river is especially important for Egypt, where about 97 percent of the population lives in the 15 to 20 km wide Nile Valley. Construction of the Aswan hydroengineering complex has helped regulate the flow of the Nile and eliminate disastrous floods and has increased the area of irrigated land. In the Sudan the waters of the Nile are important for the cotton-growing Gezira region. To regulate the river’s flow and supply water to the canals, many dams have been built on the Nile and its tributaries: the old Aswan Dam (volume of the reservoir, 5.5 cu km), the Nasser Dam (164 cu km), and the Jebel Aulia Dam on the White Nile (2.5 cu km), as well as the water-raising dams (barrages) of Isna, Nag Hammadi, Asyut, Mohammed Ali, Zifta, and Idfina in Egypt and Sennar on the Blue Nile in the Sudan.

The Nile has potential energy resources of about 50 gigawatts (GW). Hydroelectric power stations include the Aswan (capacity, 2.1 GW), Nag Hammadi, el-Fayyum on the Yusuf Canal, and Owen Falls on the Victoria Nile in Uganda (capacity, 150 megawatts). The Nile is navigable for more than 3,000 km. There is also navigation on the Yusuf, Ibrahimiya, Mansura, and Ismailia canals and on Lakes Victoria, Kyoga, Mobutu Sese Seko (Albert), and Tana. The longest navigable stretches are from Khartoum to Juba and then from Nimule to Lake Mobutu Sese Seko. Beyond this area navigation is possible only in certain sectors. The waters of the Nile basin are rich in fish. Among commercially important fish are the Nile perch, bichir, tiger fish, catfish, killifish, and carp. The largest cities along the Nile are Cairo, Khartoum, and Aswan, and, in the delta, Alexandria.

The Nile, the longest river in the world, running through Egypt and Sudan.