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Through Belgium, Fresh water and Surface water

At 31,722 km2 (12,248 sq mi)—slightly larger than Belgium—Lake Baikal is the world's seventh-largest lake by surface area, as well as the second-largest lake in Eurasia after the Caspian Sea. However, because it is also the deepest lake, with a maximum depth of 1,642 metres (5,387 feet), Lake Baikal is the world's largest freshwater lake by volume, containing 23,615.39 km3 (5,670 cu mi) of water or 22–23% of the world's fresh surface water, more than all of the North American Great Lakes combined. It is also the world's oldest lake at 25–30 million years, and among the clearest. It is estimated that the lake contains around 19% of the unfrozen fresh water on the planet.

Lake Baikal is home to thousands of species of plants and animals, many of them endemic to the region. It is also home to Buryat tribes, who raise goats, camels, cattle, sheep, and horses, on the eastern side of the lake within Buryatia, where the mean temperature varies from a winter minimum of −19 °C (−2 °F) to a summer maximum of 14 °C (57 °F). The region to the east of Lake Baikal is referred to as Transbaikalia or as the Transbaikal, and the loosely defined region around the lake itself is sometimes known as Baikalia. UNESCO declared Baikal a World Heritage Site in 1996.

Geography and hydrography

Lake Baikal is in a rift valley, created by the Baikal Rift Zone, where the Earth's crust is slowly pulling apart. At 636 km (395 mi) long and 79 km (49 mi) wide, Lake Baikal has the largest surface area of any freshwater lake in Asia, at 31,722 km2 (12,248 sq mi), and is the deepest lake in the world at 1,642 metres (5,387 feet; 898 fathoms). The surface of the lake is 455.5 m (1,494 ft) above sea level, while the bottom of the lake is 1,186.5 m (3,893 ft; 648.8 fathoms) below sea level, and below this lies some 7 km (4.3 mi) of sediment, placing the rift floor some 8–11 km (5.0–6.8 mi) below the surface, the deepest continental rift on Earth.

In geological terms, the rift is young and active—it widens about 4 mm (0.16 in) per year. The fault zone is also seismically active; hot springs occur in the area and notable earthquakes happen every few years. The lake is divided into three basins: North, Central, and South, with depths about 900 m (3,000 ft), 1,600 m (5,200 ft), and 1,400 m (4,600 ft), respectively. Fault-controlled accommodation zones rising to depths of 300 m (980 ft) separate the basins. The North and Central basins are separated by Academician Ridge, while the area around the Selenga Delta and the Buguldeika Saddle separates the Central and South basins. The lake drains into the Angara, a tributary of the Yenisey. Landforms include Cape Ryty on Baikal's northwest coast.

Baikal's age is estimated at 25–30 million years, making it the most ancient lake in geological history. It is unique among large, high-latitude lakes, as its sediments have not been scoured by overriding continental ice sheets. Russian, U.S., and Japanese cooperative studies of deep-drilling core sediments in the 1990s provide a detailed record of climatic variation over the past 6.7 million years.

Longer and deeper sediment cores are expected in the near future. Lake Baikal is the only confined freshwater lake in which direct and indirect evidence of gas hydrates exists.

The lake is surrounded by mountains; the Baikal Mountains on the north shore, the Barguzin Range on the northeastern shore and the Primorsky Range stretching along the western shore. The mountains and the taiga are protected as a national park. It contains 27 islands; the largest, Olkhon, is 72 km (45 mi) long and is the third-largest lake-bound island in the world. The lake is fed by as many as 330 inflowing rivers. The main rivers draining directly into Baikal are the Selenga, the Barguzin, the Upper Angara, the Turka, the Sarma, and the Snezhnaya. It is drained through a single outlet, the Angara.

Regular winds exist in Baikal's rift valley.

Water characteristics

Baikal is one of the clearest lakes in the world. During the winter, the water transparency in open sections can be as much as 30–40 m (100–130 ft), but during the summer it is typically 5–8 m (15–25 ft). Baikal is rich in oxygen, even in deep sections, which separates it from distinctly stratified bodies of water such as Lake Tanganyika and the Black Sea.

In Lake Baikal, the water temperature varies significantly depending on location, depth, and time of the year. During the winter and spring, the surface freezes for about 4–5 months; from early January to early May–June (latest in the north), the lake surface is covered in ice. On average, the ice reaches a thickness of 0.5 to 1.4 m (1.6–4.6 ft), but in some places with hummocks, it can be more than 2 m (6.6 ft). During this period, the temperature slowly increases with depth in the lake, being coldest near the ice-covered surface at around freezing, and reaching about 3.5–3.8 °C (38.3–38.8 °F) at a depth of 200–250 m (660–820 ft).

After the surface ice breaks up, the surface water is slowly warmed by the sun, and in May–June, the upper 300 m (980 ft) becomes homothermic (same temperature throughout) at around 4 °C (39 °F) because of water mixing. The sun continues to heat up the surface layer, and at the peak in August can reach up to about 16 °C (61 °F) in the main sections and 20–24 °C (68–75 °F) in shallow bays in the southern half of the lake.

During this time, the pattern is inverted compared to the winter and spring, as the water temperature falls with increasing depth. As the autumn begins, the surface temperature falls again and a second homothermic period at around 4 °C (39 °F) of the upper circa 300 m (980 ft) occurs in October–November. In the deepest parts of the lake, from about 300 m (980 ft), the temperature is stable at 3.1–3.4 °C (37.6–38.1 °F) with only minor annual variations.

The average surface temperature has risen by almost 1.5 °C (2.7 °F) in the last 50 years, resulting in a shorter period when the lake is covered by ice. At some locations, hydrothermal vents with water that is about 50 °C (122 °F) have been found. These are mostly in deep water but locally have also been found in relatively shallow water. They have little effect on the lake's temperature because of its huge volume.

Stormy weather on the lake is common, especially during the summer and autumn, and can result in waves as high as 4.5 m (15 ft).

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