Tien-Shan

a mountain system in Middle and Central Asia, located between 40° and 45° N lat. and between 67° and 95° E long. The western part of the Tien-Shan is in the USSR, primarily in the Kirghiz SSR; the northernmost and westernmost ranges lie in the Kazakh SSR, and the southwestern extremity of the system reaches into the Uzbek SSR and Tadzhik SSR. The eastern part of the Tien-Shan is in China. The system stretches 2,450 km from west to east; 1,200 km of this length is in the USSR. In the north the Tien-Shan is connected to the Dzungarion Alatau by the Borokhoro Range, and in the south it is linked to the Alai Range of the Gissar-AIai system. The Hi and Fergana valleys are usually considered the northern and southern boundaries of the western part of the Tien-Shan. The eastern part of the Tien-Shan is bounded by the Dzungarian Basin on the north and the Kashgar (Tarim) Basin on the south.

Terrain. The Tien-Shan consists of mountain chains stretching primarily in a more or less latitudinal direction. The only exception is the central part, the Central Tien-Shan, which includes the Meridional’nyi (Meridional) Range and contains the system’s highest peaks: Pobeda Peak (7,439 m) and the Khan-Tengri.

Several orographic regions can be identified in the Soviet part of the Tien-Shan. The Northern Tien-Shan consists of the following ranges: Ketmen’ (part of which is in China), Zailiiskii Alatau, Kungei-Alatau, and Kirghiz. The Western Tien-Shan includes the Karatau Range, the Talas Alatau Range, and the following ranges southwest of the Talas Alatau: Chatkal, Pskem, and Ugam. The ranges bordering the Fergana Valley, including the southwestern versant of the Fergana Range, are sometimes called the Southwestern Tien-Shan. The Inner Tien-Shan is south of the Kirghiz Range and the Issyk-Kul’ Basin and is rimmed on the southwest by the Fergana Range, on the south by the Kok-shaltau Range, and on the east by the Akshiirak, a massif that separates the Inner Tien-Shan from the Central Tien-Shan.

The ranges of the Northern and Western Tien-Shan gradually decrease in elevation from 4,500–5,000 m in the east to 3,500–4,000 m in the west; the Karatau Range is particularly low and has a maximum elevation of 2,176 m. These ranges have an asymmetric appearance: the northern slopes facing the Hi, Chu, and Talas basins are longer, are deeply cut by gorges, and have relative elevations of up to 4,000 m or more. The most important ranges of the Inner Tien-Shan are the Terskei-Alatau, the Borkoldoi, the Atbashi (elevations of 4,500–5,000 m), and the Kok-shaltau, which reaches an elevation of 5,982 m at Dankov Peak and constitutes the southern boundary of the Inner Tien-Shan. The more or less latitudinal trend typical of the entire Tien-Shan is especially pronounced in the Northern and Inner Tien-Shan. Three main belts of ranges can be distinguished: one is formed by the Northern Tien-Shan; the other two are the northern and southern belts of ranges of the Inner Tien-Shan. The northern belt of the Inner Tien-Shan includes the Susamyrtau, Dzhumgal-tau, Terskei-Alatau, and Dzhetim ranges and is separated from the Northern Tien-Shan by the Susamyr and Issyk-Kul’ basins. The southern belt of the Inner Tien-Shan contains the Atbashi, Naryntau, Borkoldoi, and Kokshaltau ranges and is bounded by the basins of the Middle Naryn.

The eastern part of the Tien-Shan exhibits two distinct mountain range belts separated by a belt of valleys and basins that stretches east and west. The elevations of the principal ranges are 4,000–5,000 m. The northern belt extends to 95° E long, and includes the Borokhoro, Iren-Khabyrga, Bogdo Ula, and Karlik Tag ranges. The southern belt is snorter and extends only to 90° E long. Its chief ranges are the Khalik Tau, Sarmin Ula, and Kuruk Tag. The Turfan Depression, which drops to 154 m below sea level, and the Hami Basin are located beyond the eastern Tien-Shan. The southern belt includes the intermontane basin filled by the lake Bagrash Kol.

Glacial relief forms, such as cirques and U-shaped valleys, are typical of the high-altitude regions; much talus has accumulated on the sides of the gorges, and morainal deposits are found on the valley floors. Permanently frozen rocks are almost universal at elevations above 3,200–3,400 m. The thickness of the frozen ground seldom exceeds 20–30 m but is greater than 100 m in some parts of the Aksai-Chatyrkel’ Basin.

Hydrolaccoliths and peat hummocks are found in high-altitude basins, and solifluction processes have occurred on the slopes. Debris cones are common at middle and low altitudes. Peneplains occupy substantial areas in such ranges as the Terskei-Alatau and Atbashi, and zones of foothills stretch along the bases of many of the ranges (the local terms for the foothills are prilavki and adyry). As a result, the profile of the mountains in many regions has a pronounced steplike appearance. The high-elevation basins that were freed of glaciers quite recently and are still relatively untouched by erosion processes usually have flat or mildly hilly surfaces. Lakes and marshes occupy substantial areas in these basins. The basins located below 2,500 m usually contain well-developed river valleys with numerous terraces; Issyk-Kul’ is an example of the lakes that have been preserved in some of the basins. Areas of the hilly relief known as melkosopochnik are found in certain basins, especially the Naryn and Issyk-Kul’ basins. Manifestations of argillaceous pseudokarst occur in some regions.

At the bases of the ranges there occur alluvial fans deposited by the numerous rivers. The fans often form continuous proluvial plains, which stretch for dozens of kilometers.

Geological structure and mineral resources. The mountain ranges of the Tien-Shan are composed of Paleozoic and pre-Paleozoic rocks, and the intermontane valleys and depressions are filled with Cenozoic, and, to some extent, Mesozoic deposits. The geographic divisions of the modern mountain system, which was created in the Neogene and Quarternary, do not coincide with the tectonic zonation of the Paleozoic folded structure. Within the Tien-Shan a distinction is made between the Caledonian mountains of the Northern Tien-Shan and the Hercynian mountains of the Middle and Southern Tien-Shan. The Caledonian mountains of the Northern Tien-Shan include the Kirghiz, Talas Alatau, Susamyrtau, Zailiiskii Alatau, Kungei-Alatau, Terskei-Alatau, Ketmen’, Narat, and Borto Ula ranges. The Hercynian mountains of the Middle Tien-Shan make up such ranges as the Karatau, Ugam, Pskem, Chatkal, Kurama, Dzhetim, and Dzhamantau. The Hercynian mountains of the Southern Tien-Shan include the Baubashata, Kokshaltau, Maidan Tag, Khalik Tau, Fergana, Alai, Turkestan, and Zeravshan ranges (the last three are part of the Gissar-Alai mountain system).

The Caledonian mountains of the Northern Tien-Shan are separated by faults from the Hercynian structures of the Dzungarian Alatau, Borokhoro, and Bogdo Ula (Pokoto Shan) ranges on the north and from the Hercynian mountains of the Middle Tien-Shan on the southeast and southwest. The Caledonian mountains continue northwestward into Kazakhstan. The structures of the Caledonian mountains form an arc that bulges in a southerly direction and lies parallel to the boundary with the Hercynian mountains of the Middle Tien-Shan. A miogeosynclinal zone of the Caledonian mountains extends along this boundary in the southwest, and to the northeast there is a eugeosynclinal zone. The miogeosynclinal zone is composed of crystalline basement rocks and sedimentary formations of the late Proterozoic and early Paleozoic. In the eugeosynclinal zone basic effusives and flysch deposits of the early Paleozoic are found. Throughout the Northern Tien-Shan there are detrital and volcanogenic orogenic molasses of the Ordovician, Devonian, and Carboniferous and granitoids of the early and middle Paleozoic.

The Middle Tien-Shan was a part of the miogeosynclinal zone of the Caledonian mountains. After the accumulation of the Devonian molasse, miogeosynclinal deposits of the Devonian and Carboniferous formed, and then, in the late Paleozoic, Hercynian folding occurred. The granitoids of the Middle Tien-Shan are of late Proterozoic and middle and late Paleozoic age. In the western part of the zone late Paleozoic acidic volcanogenic deposits are found. The Hercynian structures in most of the Middle Tien-Shan have a northeasterly trend. The Middle Tien-Shan is divided by the Talas-Fergana fault into two parts that have been displaced relative to one another.

The Hercynian mountains of the Southern Tien-Shan are characterized by extensive development of folded-imbricate and overlap structures involving both eugeosynclinal and miogeosynclinal deposits: the eugeosynclinal formations consist of basic volcanic rocks of the middle Paleozoic, ultrabasic rocks, and gab-broids; the miogeosynclinal rocks consist of sedimentary deposits of the early and middle Paleozoic. The molasse deposits and granitoids in the Southern Tien-Shan are of late Paleozoic age. The Hercynian folded structures in the western part of the Southern Tien-Shan lie in a latitudinal direction; they have a tangential trend in the Fergana Range, and farther to the east they exhibit a northeasterly trend. On the south the Hercynian mountains of the Tien-Shan are bounded by the Tarim and Tadzhik massifs of ancient rocks; the Tarim Basin and Tadzhik Depression formed on the sites of the massifs in the Mesozoic and Cenozoic.

The useful minerals found in the Paleozoic and pre-Paleozoic rocks of the Tien-Shan include mercury (for example, the Khai-darkan deposit), antimony (for example, the Kadamdzhai deposit), lead, zinc, silver, tin, tungsten, arsenic, gold, optical materials, phosphorites (the Karatau Basin), and mineral waters. In the Mesozoic and Cenozoic deposits of the intermontane valleys there are deposits of petroleum (as in the Fergana Valley) and brown and hard coal (near, for example, Angren, Lenger, Su-liukta, and Kok-Iangak).

Climate. The climate of the Tien-Shan is determined by the location of the mountain system in the interior of the continent, within arid desert lowlands at comparatively low latitudes. Most of the mountains lie in the temperate belt, but the ranges enclosing the Fergana Valley—the Southwestern Tien-Shan—are on the boundary with the subtropical belt and are influenced by the arid subtropics, especially at lower elevations. In general the climate is sharply continental and arid; there are 2,500–3,000 hours of sun each year. A westerly transport of air masses prevails over most of the Tien-Shan, especially at high elevations; local mountain-valley circulations are superposed on this general westerly movement. Strong local winds are observed in certain regions; examples are the ulan and santash in the Issyk-Kul’ Basin.

The high elevations and complexity and ruggedness of the relief cause marked contrasts in the distribution of temperature and precipitation. In the low-elevation valleys the mean July temperature is 20°-25°C, whereas it is 15°-17°C in the middle-elevation valleys and 5°C or lower at the bases of the glaciers. In the winter, temperatures in the glacier-firn belt fall to – 30°C. In the medium-elevation valleys cold periods often alternate with thaws, although the mean January temperature is usually below –6°C. The prevailing temperatures permit the cultivation of grapes up to an elevation of 1,400 m, the cultivation of rice up to 1,550 m (in the eastern Tien-Shan), the cultivation of wheat up to 2,700 m, and the cultivation of barley up to 3,000 m.

Precipitation in the mountains of the Tien-Shan increases with elevation. The annual precipitation in the lowlands at the foot of the mountains is 150–300 mm; in the foothills and on the low-elevation slopes it is 300–450 mm; at medium elevations it is 450–800 mm; and in the glacier-firn belt it often exceeds 800 mm, with a figure of 1,600 mm being reached at some places in the Western Tien-Shan. The intermontane basins usually have 200–400 mm of precipitation a year; their eastern parts generally receive more precipitation than their western parts. In most of the Tien-Shan precipitation reaches a maximum in the summer; in the mountains around the Fergana and Talas valleys, however, the maximum is in the spring.

Owing to the aridity of the climate, the snow line in the Tien-Shan is at elevations ranging from 3,600–3,800 m in the northwest to 4,200–4,450 m in the Central Tien-Shan; in the eastern Tien-Shan it drops to 4,000–4,200 m. There are many snowfields in the crest zone, and avalanches occur in some regions of the Tien-Shan, particularly in the spring.

The largest amounts of snow are concentrated on the northern and western slopes. At the foot of the ranges the snow usually does not stay on the ground for more than 2–3 months; at middle elevations, however, the snow cover lasts 6–7 months, and at the bases of the glaciers it lasts 9–10 months. The snow cover is usually thin in the intermontane basins, and in some areas livestock are grazed throughout the year.

Rivers and lakes. Most of the Tien-Shan is an area of runoff formation. The rivers generally originate in the snowfields and glaciers of the glacier-firn belt. Some of the rivers end in the drain-less lake basins of Middle and Central Asia or flow into the interior lakes of the Tien-Shan. Other rivers form “dry deltas” (sukhie del’ty), where their waters percolate completely into the alluvial deposits of the lowlands at the foot of the mountains; some of the water is used for irrigation. The principal rivers are located in the basins of the Syr Darya (the Naryn and Karadar’-ia), Talas, Chu, Hi (its headstreams the Kunges and Tekes and its tributary the Kash), Manassu, Tarim (the Sarydzhaz, Kokshal, and Muzart), and Konche Darya (the Khaidik Gol). The courses of most of the rivers run alternately through mountain gorges and broad valleys, where branches of the rivers form. Combined with the large drop in elevation, this characteristic of the rivers provides favorable conditions for the construction of hydroelectric power plants. A hydroelectric system is under development on the Naryn, which is the largest river in the western part of the Tien-Shan; as of 1976 the Uchkurgan Hydroelectric Power Plant had been completed, and several other hydroelectric plants, such as the Toktogul, were under construction. The rivers are fed primarily by snow; in the summer the rivers in the high-elevation regions are also fed by glaciers. The maximum runoff occurs in late spring and summer. This fact increases the economic importance of the rivers of the Tien-Shan; a substantial portion of their runoff is used to irrigate the intermontane valleys and basins and the lowlands adjacent to the Tien-Shan.

The largest lakes in the Tien-Shan are of tectonic origin and are located in intermontane basins. Examples are the brackish Is-syk-KuF, which has no outlet and never freezes, and the high-elevation (above 3,000 m) lakes Sonkel’ and Chatyrkel, which are covered with ice for much of the year. Cirque and periglacial lakes are also common; an important example is Lake Mertsbak-her, which lies between the Severnyi Inyl’chek and Iuzhnyi Inyl’-chek glaciers. The largest lake in the eastern Tien-Shan is Bag-rash Kol, which is connected with Lop Nor by the Konche Darya. There are many shallow lakes on the syrty (seeSYRT)—primarily in the region of the upper course of the Naryn River—and in depressions in morainal topography. Many dammed lakes are very deep and have steep banks; an example is Lake Sary-Chelek in the southern spurs of the Chatkal Range.

Glaciation. Glaciers cover an area of 10,200 sq km, approximately 80 percent of which is in the USSR. The greatest glaciation is concentrated in the ranges of the Central Tien-Shan. Also important for their glaciation are the Zailiiskii Alatau, Terskei-Alatau, Akshiirak, and Kokshaltau ranges, as well as the Iren-Khabyrga and Khalik Tau ranges in the eastern Tien-Shan. Compound valley glaciers flow down from the range of the Central Tien-Shan. The largest glaciers are the Iuzhnyi Inyl’chek, which has a length of 59.5 km, the Severnyi Inyl’chek, which is 38.2 km long, and the Karadzhailiau, which is 34 km long and is the most important glacier of the eastern Tien-Shan. Small valley, cirque, and hanging glaciers are most often encountered. In the Inner Tien-Shan flat-summit glaciers occurring on high-elevation peneplains are common. Most of the Tien-Shan glaciers appear to be receding, but advances of some glaciers, such as the Mushketov and Severnyi Karasai, were observed between 1950 and 1970.

Principal types of landscapes. Because of the aridity and continentality of the climate, mountain steppes and semideserts predominate in the Tien-Shan. Desert-semidesert landscapes occupy the sloping piedmont plains, the foothills of many ranges (primarily southern exposures), and the most arid parts of some inter-montane basins (for example, the western parts of the Naryn and Issyk-Kul’ basins). The predominant elevations for these landscapes are 800–1,300 m on the outer slopes of the mountains of the western part of the Tien-Shan, 1,600–1,800 m on the southern slopes of the mountains of the eastern Tien-Shan, and up to 2,000 m in some areas of the intermontane basins of the Inner Tien-Shan. The main soils are low-humus sierozems on loesses and loess-like loams; solonchaks and areas of stoney-cobble desert are also encountered. Vegetation usually covers 5—10 percent of the surface. In the Southwestern Tien-Shan, where precipitation falls primarily in the spring, there are many ephemerals and ephemeroids, such as meadow grass, desert sedge (Carex pachystylis), and Astragalus. In the remaining territory sub-shrubs, such as wormwoods and saltworts, predominate; in the eastern Tien-Shan ephedra and, in some places, thickets of sax-aul are also found.

Semideserts occupy the upper parts of the foothills and considerable areas of the intermontane basins. On the northern slopes and on the floors of the basins the semideserts are usually at elevations of 1,600–2,100 m; they may occur as low as 800 m in some parts of the wetter valleys and are encountered at elevations of up to 2,200 m on the southern slopes of the ranges of the eastern Tien-Shan. The soils are dark sierozems and gray-brown semi-desert soils with a humus content of 2.5–3.5 percent; solonchaks and solonetzes occur in low areas. Vegetation covers 15–25 percent of the surface. Wormwood-feather grass-saltwort communities predominate; in the Inner and eastern Tien-Shan Kalidium and the pea tree are also important. The semideserts are used mainly as spring and autumn pastures; their yield of edible material is 1–5 quintals per hectare (q/ha).

The most common landscape is steppe, which occurs at elevations from 1,000–1,200 to 2,500–2,600 m on north-facing slopes in the western part of the Tien-Shan and from 1,800 to 3,000 m on southern slopes of the eastern Tien-Shan. Steppes also occupy the floors of intermontane basins up to elevations of 3,000–3,200 m. The soils are light chestnut and light brown mountain-steppe soils. Shallow-sod grass-forb steppes predominate. Vegetation covers approximately 50 percent of the surface. The principal components of the plant cover are wormwood, fescue, feather grass, and wheatgrass. As one moves east, the importance of Stipa splendens (Asiatic wild grass) and the pea tree increases. The ranges of the Southwestern Tien-Shan have subtropical steppes with tall (up to 70 cm) grasses on dark leached sierozems and cinnamonic soils. Quack grass, bulbous barley (Hordeum bulbosum), inula, Prangos, and ferula are found in these areas, along with a few trees and shrubs, such as apricot and hawthorn. Within the most humid eastern parts of the intermontane basins, forb-grass meadow steppes form on dark chestnut soils. Vegetation usually covers 80–90 percent of this surface. Prostrate forms of juniper are found in the upper parts of the steppe belt. The steppes are used primarily as spring and summer pastures; their yield of edible material reaches 10 q/ha.

Rather than forming a solid belt, the forests of the Tien-Shan are found in combination with steppes and meadows. In the peripheral ranges of the Northern and Southwestern Tien-Shan the forests are at elevations of 1,500–3,000 m; in the interior mountain regions the lower and upper boundaries of the forests are higher: up to 2,200 and 3,200 m, respectively. Almost everywhere except in southwestern Kirghizia the forests are located on the northern slopes. The largest forest areas are found in the Zailiiskii Alatau Range, the Kungei-Alatau Range, the Terskei-Alatau Range, the Ketmen’ Range, and the eastern part of the Atbashi Range, as well as in the Bogdo Ula and Iren-Khabyrga ranges in the eastern Tien-Shan. In the mountains surrounding the Fergana Valley the forests grow on southwestern and southern windward slopes and thus receive considerable moisture.

The lower part of the forest belt of the Zailiiskii Alatau Range is formed of wild apple, wild apricot (uriuk), hawthorn, European aspen, and Semonov maple (Acer Semenowii). The underbrush includes such shrubs as barberry, buckthorn, honeysuckle, spindle tree, and wild rose on gray forest soils. Above 2,000–2,200 m the hardwood forests give way to spruce forests on dark-colored mountain-forest soils with a high (up to 15 percent) humus content. The chief forest tree in the Inner and eastern Tien-Shan is the spruce, which is confined to parts of north-facing slopes. On the floors of the broad and U-shaped valleys and on the better-illuminated parts of the slopes, forests grow in combination with subalpine-type forb meadows (geranium, lady’s-man-tle, phlomis, and iris). The meadows are used as summer pastures; their yield of edible material is 15–20 q/ha. On south-facing slopes in the forest-meadow-steppe belt, steppes with areas of sparse juniper (archa) forest predominate.

The nut-fruit forests of the Southwestern Tien-Shan, which form on black-brown mountain-forest soils, are unique. Some investigators consider them to be relicts preserved from the Neogene. These parklike forests are composed of English walnut, apple, and maple trees with a rich underbrush that includes honeysuckle, cherry plum, almond, wild rose, and buckthorn. In some valleys—for example, near Arslanbob—there are almost pure stands of English walnut. Above 2,000 m the nut-fruit forests give way to conifer forests of spruce and fir. Pistacia groves occur in some areas of the Southwestern Tien-Shan. The forests of the Tien-Shan are very important for water storage. Nuts and commercial timber are obtained from the nut-fruit forests.

Subalpine and alpine meadows occur primarily on north-facing slopes above 3,000–3,200 m. Rather than forming a solid belt, they usually alternate with almost-vegetation-free cliffs and talus slopes. Low-growing forb-sedge meadows, which are often marshy, occur on thin mountain-meadow and meadow-bog soils. Such meadows are used as short-term summer pastures; their yield of edible material is 5–10 q/ha.

On the high syrty of the Inner and Central Tien-Shan, at elevations from 3,000–3,200 to 3,400–3,700 m, there are found “cold desert” landscapes, whose vegetation is represented by isolated clusters of caespitose grasses and communities of pulvinate plants, such as dryas. In addition, wormwood occurs in the areas that receive more warmth. The soils are low in humus and frequently have a takyr-like character (seeTAKYR). In some places meadows of sedge and Kobresia are found. They are used as summer pastures; their yield of edible material ranges from 3–5 q/ha to 15 q/ha on the Kobresia meadows.

Above 3,400–3,600 m the landscapes of the glacier-firn belt are universal. This zone is characterized by glaciers, snowfields, talus slopes, and cliffs. There is no soil cover, and vegetation is represented primarily by occasional mosses and lichens.

Fauna. The plains, foothills, and low-mountain regions of the Tien-Shan are characterized by desert and steppe fauna. Examples are the goitered gazelle, the polecat, the Tolai hare, the suslik, jerboas, gerbils, the mole lemming, the field mouse Apodemus sylvaticus, and the Turkestan rat. Reptiles include snakes (viper, moccasin, and Elaphe dione) and lizards. Birds include the lark, wheatear, bustard, sandgrouse, chukar partridge, and imperial eagle. Mammal representatives of the forest fauna of the middle-elevation mountains include the wild boar, lynx, brown bear, old world badger, wolf, fox, marten, roe deer, and an acclimatized form of the squirrel Sciurus vulgaris exalbidus; common birds are the crossbill and nutcracker. At high elevations and in some middle-elevation areas there occur marmots, pikas, silver voles (Alticola argentata). and narrow-skulled voles (Microtus gregalis), mountain goats (teke), argali, and the stoat; in addition, an occasional snow leopard is encountered. Birds include the alpine chough, the horned lark, bramblings, the Himalayan snow cock, eagles, and vultures. Such waterfowl as ducks and geese inhabit the lakes. Swans visit Issyk-Kul’ during their migration; birds encountered at Bagrash Kol include the cormorant and the black stork. Many lakes are rich in such fish as the osman (Diptychus), chebak, and marinka (Schizothorax).

Protected regions. As of 1975, five preserves had been established in the Soviet part of the Tien-Shan: the Issyk-Kul’ Preserve, the Alma-Ata Preserve, the Aksu-Dzhabagli Preserve, the Sary-Chelek Preserve, and the Chatkal Mountain and Forest Preserve. A number of sancturies have also been established in the Soviet Tien-Shan—for example, in the area occupied by the nut-fruit forests of the Southwestern Tien-Shan.

The economy of the Tien-Shan region is discussed in KAZAKH SOVIET SOCIALIST REPUBLIC, KIRGHIZ SOVIET SOCIALIST REPUBLIC, and SINKIANG-UIGHUR AUTONOMOUS REGION.