Tien Shan

Physiography

The relief is characterized by a combination of mountain ranges and intervening valleys and basins trending generally from east to west. The deepest depression in the eastern Tien Shan is the Turfan (Turpan) Depression, within which is the lowest point in Central Asia—505 feet (154 metres) below sea level. Thus, the differences in elevation in the Tien Shan are extreme, exceeding 4.5 miles (7 km). The eastern extension of the Turfan Depression is the Hami (Qomul) Basin; both basins are bounded to the north by the Bogda Mountains, with elevations of up to 17,864 feet (5,445 metres), and by the eastern extremity of the Tien Shan, the Karlik Mountains, which reach a maximum elevation of 16,158 feet (4,925 metres).

The ranges are of the alpine type, with steep slopes; glaciers occur along their crests. The basins are bounded to the south by the low-rising Qoltag Mountains. West of the Turfan Depression is one of the greatest mountain knots of the eastern Tien Shan: the Eren Habirga Mountains, which reach elevations of 18,200 feet (5,550 metres). The ridge has considerable glacial development, as well as numerous forms of relief that indicate the area was the site of ancient glaciation.

West of longitude 84° E, the eastern Tien Shan ridges fork, trending to the southwest and northwest, and enclose the vast depression of the Ili (Kazakh, Ile; Chinese, Yili) River valley in Kazakhstan, which gradually widens and loses elevation as it proceeds westward. It is bounded to the north by the Borohoro Mountains, which have glaciers in the eastern part and are characterized by steeply sloping ridges. This range also gradually descends westward, where at an elevation of 6,801 feet (2,073 metres) lies the great undrained Lake Sayram. The Ili depression is bounded to the south by the highest mountains in the central Tien Shan—the Halik Mountains, reaching heights up to 22,346 feet (6,811 metres), and the isolated Ketpen (Ketmen) Range, which rises to an elevation of 11,936 feet (3,474 metres) in the central part of the depression.

The northern extremity of the part of the Tien Shan in Kazakhstan forms the Zhonggar (Dzungarian) Alataū Range (14,645 feet [4,464 metres]), which is subject to considerable glacial action. To the south the Ile Alataū (Trans-Ili) Range rises abruptly above the Ili depression to a height of 16,315 feet (4,973 metres). The successive transition of climatic zones, determined by elevation, from arid and dry steppe at lower levels to glacial at the summit, is evident on the northern slopes of this range. The Kyrgyz Ala (Qyrghyz) and Talas Alataū ranges, rising above 13,000 feet (4,000 metres) and located farther west, also belong to the outer chain of the northern Tien Shan. There is a great difference in elevation between these outer mountain ridges and the plains at their base. Streams, therefore, usually plunge down the mountain sides through deep gorges and, as they flow out onto the plains, form vast fan-shaped deposits of silt and mud. On the fertile land formed by this process are located many oases and population centres, including the cities of Almaty in Kazakhstan and Bishkek in Kyrgyzstan. The Küngöy Ala (Küngey Alataū) and Teskey Ala (Terskey-Alataū) ranges also belong to the northern Tien Shan. The Teskey Ala rises to a height of about 17,300 feet (5,300 metres) and borders the vast Lake Ysyk basin, the centre of which is filled by Lake Ysyk (Ysyk-köl).

The western portion of the Ak-Say (Toxkan in China) River basin and most of the Naryn River basin are situated within the inner Tien Shan. This region is characterized by the alternation of comparatively short mountain ranges and valleys, both extending east and west. The predominant elevations of the mountains vary from approximately 10,000 to 15,000 feet (3,000 to 4,600 metres), while the elevations of the depressions that separate them vary from 6,000 to 10,500 feet (1,800 to 3,200 metres). The most important ranges are Borkoldoy, Dzhetym, At-Bashy, and the Kakshaal (Kokshaal-Tau) Range, in which Dankova Peak reaches a height of 19,626 feet (5,982 metres).

The elevation of the mountains increases in the Sary-Jaz (Saryzhaz) Mountains in the central Tien Shan, which lies to the east of the Ak-Shyyrak (Akshiyrak) Range. The separate ranges gradually converge, forming the high-elevation mountain knot already mentioned, which includes Khan Tängiri Peak and Victory Peak.

In contrast to most of the Tien Shan ranges, which run approximately east-west, the Fergana Kyrka Mountains, separating the inner region from the western and southern Tien Shan, extends from southeast to northwest. Its maximum elevation is 16,207 feet (4,940 metres). The southwestern slopes display a variety of climatic zones in the course of their gradual descent.

The western Tien Shan ranges lie north of the Fergana Valley. Several short but high and steep ranges running southwest-northeast there meet the southern sides of ranges running westward and northwestward. The highest peak is in the Chatkal Mountains (14,773 feet [4,503 metres]), and the predominant elevations vary between 7,500 and 10,500 feet (2,300 and 3,200 metres).

The southern Tien Shan ranges (including Turkistan, Zeravshan, and Alay, among others) border the Fergana Valley on the south and extend chiefly east and west. The maximum elevation is 18,441 feet (5,621 metres), with several peaks above 15,000 feet. To the south the Tien Shan meets the Pamirs. Foothills approach the northern slopes of the ranges, and there are oases on the plains below the mountains.