Pamirs


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Pamirs

 

(the name may derive from the ancient Iranian pai-mir, “foot of Mithra,” god of the sun), a mountainous land in Middle Asia, mainly in the Gorno-Badakhshan AO of the Ta-dzhik SSR.

The natural boundaries of the Pamirs have not been clearly established. The Pamirs are usually defined as the territory bounded by the Transalai Range on the north, by the SarykoF Range on the east, by Lake ZorkuP, the Pamir River, and the headwaters of the Piandzh River on the south, and by the north-south segment of the Piandzh River Valley on the West. The eastern parts of the Petr Pervyi and Darvazskii ranges are included in the Pamirs on the northwest. Within the Soviet Union the Pamirs cover an area 250 km long and 275 km wide. Some geographers define the Pamirs more narrowly as only the eastern part of this territory (K. V. Staniukovich, E. M. Murzaev), whereas many others regard the Pamirs as a broader area, including the neighboring mountains on the east (N. A. Gvozdet-skii, R. D. Zabirov) and parts of other regions (O. E. Agakhaniants).

The relief of the Pamirs includes east-west and north-south ranges, with the former found mainly in the west. The east-west ranges coincide with large folded structures (anticlinoria), and the north-south ranges were formed by transverse uplifts superimposed over these basic trends. In the north the east-west Transalai Range averages 6,000 m, rising to 7,134 in Lenin Peak. South of the Transalai Range several north-south ranges stretch from west to east: the Akademiia Nauk, the Zulumart, and the Sarykol’, which divides the Tarim and Amu Darya basins.

The Akademiia Nauk Range reaches its maximum elevation in Communism Peak (7,495 m), the highest point in the USSR. Its eastern slope is covered by the snow and ice of the firn region of the Fedchenko Glacier, and its western slope forms a high barrier facing several parallel east-west ranges. As one moves from north to south, these ranges are the Petr Pervyi Range with Moscow Peak (6,785 m), the Darvazskii Range with Arnavad Peak (6,083 m), the Vanch Range, and the Iazgulem Range with Revolution Peak (6,974 m). To the east of the Iazgulem Range, in the central Pamirs, is the east-west Muzkol Range, which reaches 6,233 m in Soviet Officers Peak. South of it stretches a range called the Rushan in the west and the Severo-Alichur (Bazardara) in the east. Farther south are the Shugnan and Iuzhno-Alichur ranges. The extreme southwestern part of the Pamirs is occupied by the Shakhdara Range, which consists of north-south (Ishkashim Range) and east-west segments with Mayakovsky Peak (6,096 m) and Karl Marx Peak (6,726 m). In the extreme southeast, south of the Pamir River and Lake Zorkul’, is the Vakhan Range, an easterly continuation of the Shakhdara Range.

The Pamirs are divided into an eastern and a western region according to relief. The eastern Pamirs are dominated by an ancient medium-mountain relief whose foundation has been greatly uplifted by recent tectonic movements. Although absolute elevations range from 4,000 m to 6,000 m, relative elevations usually do not exceed 1,000–1,500 m. The ranges and massifs have mostly soft, rounded outlines, and the valleys and un-drained basins between them, lying at elevations of 3,700–4,200 m, are broad, flat-bottomed, and filled with thick beds of loose detrital (proluvial and moraine). Some of the uplifts, such as the Muzkol Range, have high-mountain relief on the crest.

A rugged high-mountain relief predominates in the western Pamirs, where narrow, alpine ranges capped by snow and glaciers alternate with deep, narrow canyons with turbulent, high rivers. The crests of the ranges are 2,000–3,500 m above the valley floors, and bare cliffs and talus fields are a dominant feature of the mountains. Loose deposits in the form of debris cones, moraine accumulations, and fluvioglacial and alluvial terraces cover a small area. The debris cones and terraces are about the only places suitable for human settlement and economic activity. Also widespread are such glacial relief forms as trough valleys, sheepback rocks, mouth bars, cirques, and horn peaks.

The eastern Pamirs type of relief gives way to the western Pamirs type gradually. The western Pamirs have few eastern Pamirs relief features; only in a few places have small, flat or slightly rolling surfaces been preserved at elevations of about 4,000–4,600 m. Above these heights are rugged alpine forms, and below them are deep river-erosion forms made more complex by the activity of ancient valley glaciers and postglacial erosion. The conventional boundary between the eastern and western Pamirs relief is a line running from the crest of the Zulumart Range to the Karabulak and Pshart passes and from there to the western end of Lakes Sarezskoe and Iashil’kul’ and the middle course of the Pamir River.

The present structure and relief of the Pamirs are the result of intensive Cenozoic movements that transformed the Pamirs into a high country; the earthquakes in the region indicate that these movements are continuing in the present. The formation of the present relief dates from the middle of the Miocene, when continental conditions were established everywhere in the Pamirs and river erosion began. Erosion first developed along the margins of the mountain country, primarily in the western Pamirs and the mountains adjoining the Sarykol’ Range on the east, and gradually spread to the interior. As a result, the river valleys are deep along the periphery of the Pamirs, becoming shallower toward the center. Regressive erosion has not yet spread to the eastern Pamirs, so that the smoothed-out relief of the region preserves relict features.

Geological structure and minerals. Several arc-shaped zones curving to the north may be discerned in the Pamirs as one moves from north to south. These zones are divided by faults and differ in their geological structure.

The outer zone—the northern slope of the Transalai Range— is composed of conglomerates, sandstones, clays, limestones, and volcanic rock of the Upper Permian, Mesozoic, and Cenozoic with a total thickness of 12–14 km. Intensive deformations that began in the middle of the Oligocene created complex folds and overthrusts. The zone’s present structures may have been torn from their original foundation and shifted to the north in the form of a shield nappe.

The northern zone of the Pamirs—the area south of the crest of the Transalai Range—consists of schists of the Upper Precambrian, Paleozoic marbleized limestones and sandstones, and Paleozoic clayey, carbonate, and volcanic rocks breached between the Triassic and Middle Jurassic by granitoid intrusives. The folded structure of the zone, a complex meganticlinorium broken into blocks by more recent movements, also developed at this time.

The central zone of the Pamirs has a nappe structure. The autochthon (parautochthon) is composed of schist and weakly metamorphosed rocks of the Upper Precambrian and also thick sedimentary and sedimentary-volcanic strata of the Middle Paleozoic-Upper Cretaceous (chiefly marine and some bauxite-bearing rocks). The allochthon consists of thin layers of Paleozoic sedimentary rock and thick beds from the Mesozoic-Mio-cene with horizons of volcanic rock. The rocks of the autochton were breached by Paleogene and Neogene intrusions, simultaneously undergoing intensive metamorphosis in places. There are granitoids believed to be of Paleogene and Neogene age.

The Rushan-Pshart zone is composed of terrigenous-carbonate-siliceous beds of the Upper Paleozoic and Mesozoic containing bands of diabase and spilite. The beds have been compressed into folds tilted to the north and have been dislocated by over-thrusts. These rocks are breached by intrusions of Jurassic, Cretaceous, and Eocene granitoids.

In the southeastern Pamirs there are thick terrigenous marine beds of the Upper Paleozoic; siliceous-carbonate and flyschoid rocks of the Triassic and Jurassic; and multicolored sandstones, conglomerates, and red terrigenous-tufogenic rocks of the Cretaceous-Miocene, breached by granitoids of the Upper Cretaceous and Eocene. The southeastern zone is a huge synclinorium complicated by overthrusts and displacements.

The southwestern zone of the Pamirs is composed of schists, gneisses, and marbles of the Precambrian breached by intrusions of Cretaceous and Oligocene-Neogene granitoids. This zone is usually regarded as a median mass. It is also possible that the zone is allochthonous with respect to the surrounding folded structures.

The position of the Pamirs in the geological structure of Central Asia has been interpreted in different ways. Some geologists extend the Pamirs zone southwest and east. Others believe that the Pamirs are divided from the Kunlun in the east either by a deep fault or by a displacement with an amplitude of 150–200 km.

The minerals of the Pamirs, formed primarily as a result of Cenozoic magmatism and metamorphosis, include deposits of rock crystal, rare metals, mercury, boron, fluorite, Iceland spar, lazurite, spinel, and placer gold. Bauxite deposits are associated with the crust of weathering between the Triassic and Permian in the Pamirs’ central zone.

Climate. The Pamirs have a severe continental high-mountain climate, especially in the east, where enclosed depressions retain cold air. Because the Pamirs are in the subtropical belt, air masses from the temperate latitudes predominate here in winter and tropical air masses in summer. The mean January temperature in the eastern Pamirs at elevations of about 3,600 m is — 17.8° C. Winter lasts from October through April, and the absolute minimum temperature may drop to — 50°C. During the short and cold summers temperatures do not rise above 20°C. The mean July temperature at about 3,600 m is 13.9°C. In the Murgab and Oksu valleys and in the undrained depressions (Lake Karakul’) permafrost rock is widespread. In the valleys of the western Pamirs the mean January temperature at about 2,100 m is -7.4°C, and the July temperature is 22.5°C. The growing season, with temperatures of 5°C, is 223 days in Khorog and 140 days in Murgab.

The amount of annual precipitation is most strongly influenced by cyclonic processes with air masses moving in a southwesterly direction. The total annual precipitation ranges from 92 mm to 260 mm in the valleys of the western Pamirs and from 60 mm to 119 mm in the eastern Pamirs. The amount increases in high-mountain regions and on mountain slopes, reaching 1,100 mm on the Fedchenko Glacier. In the western Pamirs the maximum precipitation occurs in March and April and the minimum during the summer; in the eastern Pamirs the maximum falls in May and June and the minimum in August. During the summer the eastern Pamirs are sometimes affected by the moist tropical air masses from India’s monsoon circulation.

Glaciation. There are about 3,000 glaciers, covering some 8,400 sq km. The major areas of glaciation are the Akademiia Nauk, Transalai, Rushan, Severnyi Alichur, Iazgulem, Petr Per-vyi, Darvazskii, and Zulumart ranges. The snowline is at 4,000–4,400 m in the northwest and at 5,000–5,200 m in the central and eastern regions. Valley glaciers predominate in the western Pamirs. The largest valley glacier is the 77-km-long Fedchenko Glacier in the Akademiia Nauk Range. The major glaciers in the northwest are the Grumm-Grzhimailo (36.7 km), Garmo (27.5 km), Surgan (24 km), Geograficheskoe Ob-shchestvo (21.5 km), and Fortambek (20 km). The largest glacier in the Transalai Range is the Bol’shoi Saukdara Glacier (25 km). Some of the glaciers, such as Medvezhii Glacier in the upper reaches of the Vanch River and Lenin Glacier in the Transalai Range, periodically move rapidly several kilometers down the valleys, traveling at speeds of up to 100 m per day. In the eastern Pamirs small valley, slope, and cirque glaciers predominate. In terms of the size of individual glaciers and the total area covered by glaciers, contemporary glaciation is considerably less than ancient glaciation.

Rivers and lakes. Most of the rivers belong to the Amu Darya basin. The largest river is the Piandzh. Its right tributaries are the Gunt with the Shakhdara, the Bartang (called Oksu in its upper reaches and Murgab in its middle course), the Iazgulem, and the Vanch. The headwaters of the Obikhingou and Muksu, which drain the Vakhsh basin, are in the northwestern Pamirs. A small number of rivers belong to the interior basins of the Pamirs (Karadzhilga, Muzkol) and the Tarim basin (Markansu). The rivers are fed by snow and glaciers, and high water occurs in the summer. The largest lake is Karakul’, an undrained salt lake lying in a tectonic depression. Other large lakes are Rangkul’, Shorkul’ (connected by a stream), and Zorkul’, a moraine-dammed lake. The smaller Iashil’kul’ and Sarez lakes, which have outlets, were formed by the damming up of rivers by cave-ins.

Basic landscapes. The natural world of the Pamirs resembles that of Central Asia and is related to the physical-geographic region of the Central Asian Highlands. The differences in landscape in the Pamirs are determined primarily by altitudinal zo-nation, by the distribution of eastern and western Pamirs relief, and by the sharply decreasing precipitation and increasingly continental climate as one moves from the northwest to the east and southeast. Vegetation is extremely sparse, and bare rocky surfaces or surfaces covered with gravel and boulder loam predominate.

In the eastern Pamirs, in areas with a flat relief, the dominant landscape is that of cold high-mountain deserts and rocky high-mountain regions. There are almost no trees, and the flora consists of low plants adapted to harsh conditions. On the flat floors of the valleys and depressions and on the dry mountain slopes grow low winter fat shrubs, cushion plants (Acantholimon, Oxy-tropis), Pamir tansy, Astragalus, and local wormwood and onion (Allium) species. Plants of the iris family and Poa grow in the sparse-grass steppes. Sedge and cobresia meadows, called sazy, are found on the floors of moist valleys. The meager fauna of the eastern Pamirs is represented by the mountain sheep (ar-khar), long-tailed marmot, long-eared pika, and woolly hare. Birds include the Tibetan mountain partridge, Tibetan sand-grouse, ibisbill, Tibetan raven, horned lark, and snow vulture.

The landscapes of the western Pamirs have a richer vegetation than those of the eastern Pamirs, although wormwood and sax-aul predominate in the deserts in the lower parts of mountain valleys. Above 3,200 m are found prickly cushion plants, such as Acantholimon and spiny Astragalus. Above 3,600 m are steppes with fescue and feathergrass; yugan (Prangos) and kamol grow on talus slopes. At 3,800 m to 4,300 m there is low cryophilic grass, and above 4,500–4,700 m, sparse subnivean vegetation. Along the riverbeds of the western Pamirs there are occasional thickets (called tugai) of willow, buckthorn, poplar, birch, and hawthorn. In places trees and shrubs grow to an elevation of 3,900 m (willow, birch, and savin). On irrigated land (debris cones, terraces) grapes, apricots, apples, pears, walnuts, and mulberry trees are cultivated. The mountains of the western Pamirs are inhabited by mountain goats (kiik), brown bears, wolves, foxes, snow leopards, stone marten, Tolai (Cape) hares, and bats. Birds include the Indian oriole, dark-breasted snow cock, rock partridge, shrike, and Indian paradise flycatcher. The Pamirs have few fish, and the only known species are schizo-thoracins and Tibetan chars.

The high peaks of the Pamirs attract many Soviet mountain climbers.

REFERENCES

Agakhaniants, O. E. Osnovnye problemy fizicheskoi geografii Pamira, parts 1–2. Dushanbe, 1965–66.
Markov, K. K. “Geomorfologicheskii ocherk Pamira.” Tr. In-tafizicheskoi geografii AN SSSR, 1935, fasc. 17, no. 1.
Gvozdetskii, N. A. Pamir. Moscow, 1968.
Barkhatov, B. P. Tektonika Pamira. Leningrad, 1963.
Muratov, M. V., and I. V. Arkhipov. “O tektonicheskom polozhenii Pamira v sisteme skladchatykh gornykh sooruzhenii Iugo-Zapadnoi i Tsentral’noi Azii.” Biul. Mosk. obshchestva ispytatelei prirody: Otdel geologii, 1961, vol. 36, fasc. 4.
Peive, A. V., et al. “Tektonika Pamiro-Gimalaiskogo sektora Azii.” In Gimalaiskii i al’piiskii orogenez. Moscow, 1964.
Chediia, O. K., and V. V. Loskutov. “Paleogeografiia Pamira i sopredel’-nykh stran v pliotsen-chetvertichnoe vremia.” In Chetvertichnyi period i ego istoriia. Moscow, 1965.
Vasil’ev, V. A. Kainozoi Pamira (kontinental’nye otlozheniia). Dushanbe, 1966.
Shvol’man, V. A. “Melovye i paleogenovye otlozheniia Iugo-Vostoch-nogo Pamira i ikh polozhenie v sovremennoi strukture.” Biul. Moskovskogo obshchestva ispytatelei prirody: Otdel geologicheskii, 1973, vol. 48, fasc. 1.
Zabirov, R. D. Oledenenie Pamira. Moscow, 1955.
Staniukovich, K. V. Rastitel’nyi pokrov Vostochnogo Pamira. Moscow, 1949.
Ikonnikov, S. S. Opredelitel’ rastenii Pamira. Dushanbe, 1963.
Fiziko-geograficheskoe raionirovanie SSSR. Moscow, 1968.
Atlas Tadzhikskoi SSSR. Dushanbe-Moscow, 1968.

N. A. GVOZDETSKII, T. K. ZAKHAROVA, and V. A. SHVOL’MAN (geological structure and minerals)

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