Baikal (known to the Mongols as Dalai-nor, and to the Turkish tribes as Bai-kul), a lake of East Siberia, the sixth in size of all the lakes of the world and the largest fresh-water basin of Eurasia. It stretches from S.W. to N.E. (51° 29′ to 55° 50′ N. lat. and 103° 40′ to 110° E. long.), separating the government of Irkutsk from that of Transbaikalia, and has a length of 386 m. and a width of from 20 m. to 50 m. Its southern extremity penetrates into the high plateau of Asia, and the lake lies entirely in the Alpine zone which fringes that plateau on the north-west. Its area is 13,200 sq. m., i.e. nearly as great as Switzerland. The length of its coast-line is 525 m. along the western, and 640 m. along the eastern shore. Its altitude has been estimated at 1587 ft. (Chersky) and at 1679 ft. (Suess) - 118 ft. above the level of the Angara at Irkutsk (Zapiski Russ. Geog. Soc. xv., 1885); but 1500 ft. would seem to be a more correct altitude (Izvestia East Sib. Branch, xxviii. 1, 1897). Its level is subject to slight oscillations, and after a heavy five weeks' rain in 1869 it rose 7 ft., an immense territory at the mouth of the Selenga being submerged.
A hydrographic survey of this lake was made by Drizhenko in 1897-1902. The elongated hilly island of Olkhon, and the peninsula of Svyatoi Nos, which forms its continuation on the opposite eastern shore, divide the lake into two basins. The deepest part is in the south-east, at the foot of the Khamar-daban border-ridge of the high plateau. An elongated trough, 66 m. long, reaches there a depth of over 600 fathoms, with a maximum depth of 880 fathoms, i.e. about 5280 ft. below the level of the ocean. As a rule the bottom of the lake has very steep slopes: the 100-fathom and even the 250-fathom lines run close to the shores, that is to say, the steepness of the surrounding mountains (4600 to 6000 ft.) continues beneath the surface. At the mouth of the Selenga, however, which enters from the south-east, pouring into it the waters and the alluvial deposits from a drainage area of 173,500 sq. m., a wide delta is thrust out into the lake, reducing its width to 20 m. and spreading under its waters, so as to leave only a narrow channel, 230 to 247 fathoms deep, along the opposite coast. The depth of the middle portion of the lake has not yet been measured, but must exceed 500 fathoms.
It was expected that an underground ridge would be found connecting Olkhon with Svyatoi Nos; but depths exceeding 622 fathoms have been sounded even along that line. As to the northern basin, the configuration of its bottom is in accordance with the high mountains which surround it, and most of its area has a depth exceeding 400 fathoms, the maximum depths along three lines of soundings taken across it being 491, 485, and 476 fathoms respectively. The water is beautifully clear.
The surface-layers of this immense basin are heated in the summer up to temperatures of 55&FRAC12;° to 57° F., both close to the shores and at some distance from the mouth of the Selenga; but these warmer layers are not deep, and a uniform temperature of nearly 39° F. is generally found at a depth of 20 fathoms, as also on the surface in the middle of the lake. At a depth of 500 fathoms there is a nearly uniform temperature of 38°. At various places round the shores, e.g. the mouth of the Barguzin, hot springs exist. The lake freezes usually at the end of December, or in the beginning of January, so solidly that a temporary post-horse station is erected on the ice in the middle of the lake, and it remains frozen till the second half of May. The evaporation from this large basin exercises a certain influence on the climate of the surrounding country, while the absorption of heat for the thawing of the ice has a notable cooling effect in early summer.