Altai (in Mongolian Altain-ula, the "Mountains of Gold"), a term used in Asiatic geography with various significations.
The Altai region, in West Siberia and Mongolia, is similar in character to Switzerland, but covers a very much greater area. It extends from the river Irtysh and the Dzungarian depression (46°-47° N) northwards to the Trans-Siberian railway and to the Sayan Mountains.
The backbone of the region is the Sailughem or Silyughema mountains, also known as Kolyvan Altai, which stretch north-eastwards from 49° N and 86° E towards the western extremity of the Sayan mountains in 51° 60' N and 89° E. Their mean elevation is 5000-5500 ft. The snow-line runs at 6700 ft. on the northern versant and at 7800 ft. on the southern, and above it the rugged peaks tower up some 3200 ft. more. Passeses across the range are few and difficult, the chief being the Ulan-daban at 9275 ft. (9445 ft. according to Kozlov), and the Chapchan-daban, at 10,555 ft-, in the south and north respectively. On the east and south-east this range is flanked by the great plateau of Mongolia, the transition being effected gradually by means of several minor plateaus, such as Ukok (7800 ft.) (with Pazyryk), Chuya (6000 ft.), Kendykty (8200 ft.), Kak (8270 ft.), Suok (8500 ft.), and Juvlu-kul (7900 ft.).
This region is studded with large lakes, i.e. Ubsa-nor (2370 ft. above sea-level), Kirghiz-nor, Durga-nor and Kobdo-nor (3840 ft.), and traversed by various mountain ranges, of which the principal are the Tannu-ola, running roughly parallel with the Sayan mountains as far east as the Kosso-gol (iooc-ioi° E. long.), and the Khan-khu mountains, also stretching west and east.
The range of the Altai proper, known also as the Ek-tagh, Mongolian Altai, Great Altai and Southern Altai, likewise extend in two twin parallel chains eastwards as far as 99°, if not farther.
The Ek-tagh or Mongolian Altai, which separates the Kobdo basin on the north from the Irtysh basin on the south, is a true border-range, in that it rises in a steep and lofty escarpment from the Dzungarian depression (1550 to 3000 ft.), but descends on the north by a relatively short slope to the plateau (4000-5500 ft.) of north-western Mongolia. East of 94° the range is continued by a double series of mountain chains, all of which exhibit less sharply marked orographical features and are at considerably lower elevations. The southern chain bears the names of Kara-adzirga and Burkhan-ola, and terminates in about 99°; but the northern range, the principal names of which are Artsi-bogdo and Saikhat, extends probably most of the way to the great northward bend of the Yellow River round the desert of Ordos. Whereas the western Ek-tagh Altai rises above the snow-line and is destitute of timber, the eastern double ranges barely touch the snow-line and are clothed with thick forests up to an altitude of 6250 ft. The slopes of the constituent chains of the system are inhabited principally by nomad Kirghiz.
The north-western and northern slopes of the Sailughem mountains are extremely steep and very difficult of access. On this side lies the culminating summit of the range, the double-headed Belukha (the Mont Blanc of the Altai), whose summits reach 14,890 and 14,560 ft. respectively, and give origin to several glaciers (30 sq. m. in aggregate area). Here also are the Kuitun (12,000 ft.) and several other lofty peaks. Numerous spurs, striking in all directions from the Sailughem mountains, fill up the space between that range and the lowlands of Tomsk, but their mutual relations are far from being well known. Such are the Chuya Alps, having an average altitude of 9000 ft., with summits from 11,500 to 12,000 ft., and at least ten glaciers on their northern slope; the Katun Alps, which have a mean elevation of about 10,000 ft. and are mostly snow-clad; the Kholzun range; the Korgon (6300 to 7600 ft.), Talitskand Selitsk ranges; the Tigeretsk Alps, and so on.
Several secondary plateaus of lower altitude are also distinguished by geographers, The Katun valley begins as a wild gorge on the south-west slope of Belukha; then, after a big bend, the river (400 m. long) pierces the Katun Alps, and enters a wider valley, lying at an altitude of from 2000 to 3500 ft., which it follows until it emerges from the Altai highlands to join the Biya in a most picturesque region. The Katun and the Biya together form the Ob.
The next valley is that of the Charysh, which has the Korgon and Tigeretsk Alps on one side and the Talitsk and Bashalatsk Alps on the other. This, too, is very fertile. The Altai, seen from this valley, presents the most romantic scenes, including the small but deep Kolyvan lake (altitude, 1180 ft.), which is surrounded by fantastic granite domes and towers.
Farther west the valleys of the Uba, the Ulba and the Bukhtarma open south-westwards towards the Irtysh. The lower part of the first, like the lower valley of the Charysh, is thickly populated; in the valley of the Ulba is the Riddersk mine, at the foot of the Ivanovsk peak (6770 ft.), clothed with beautiful alpine meadows. The valley of the Bukhtarma, which has a length of 200 m., also has its origin at the foot of the Belukha and the Kuitun peaks, and as it falls some 5000 ft. in less than 200 m., from an alpine plateau at an elevation of 6200 ft. to the Bukhtarma fortress (1130 ft.), it offers the most striking contrasts of landscape and vegetation. Its upper parts abound in glaciers, the best known of which is the Berel, which comes down from the Byelukha. On the northern side of the range which separates the upper Bukhtarma from the upper Katun is the Katun glacier, which after two ice-falls widens out to 700-900 yards. From a grotto in this glacier bursts tumultuously the Katun river.
The middle and lower parts of the Bukhtarma valley have been colonized since the 18th century by runaway Russian peasants - serfs and nonconformists (Raskolniks) - who created there a free republic on Chinese territory; and after this part of the valley was annexed to Russia in 1869, it was rapidly colonized. The high valleys farther north, on the same western face of the Sailughem range, are but little known, their only visitors being Kirghiz shepherds.
Those of Bashkaus, Chulyshman, and Chulcha, all three leading to the beautiful alpine lake of Teletskoye (length, 48 m.; maximum width, 3 m.; altitude, 1700 ft.; area, 87 sq. m.; maximum depth, 1020 ft.; mean depth, 660 ft.), are only inhabited by nomad Telenghites or Teleuts. The shores of the lake - reminding a visitor somewhat of the Swiss lake of Lucerne rise almost sheer to over 6000 ft. and are too wild to accommodate a numerous population. From this lake issues the Biya, which joins the Katun at Biysk, and then meanders through the beautiful prairies of the north-west of the Altai.
Farther north the Altai highlands are continued in the Kuznetsk district, which has a slightly different geological aspect, but still belongs to the Altai system. But the Abakan river, which rises on the western shoulder of the Sayan mountains, belongs to the system of the Yenisei. The Kuznetsk Ala-tau range, on the left bank of the Abakan, runs north-east into the government of Yeniseisk, while a complexus of mountains (Chukchut, Salair, Abakan) fills up the country northwards towards the Trans-Siberian railway and westwards towards the Ob.