Lake Baikal (Oldest Fresh Water Lake on Earth), Southern Siberia, Russia and Mongolia (Basin countries)

Lake Baikal is the largest (by volume) freshwater lake in the world, containing roughly 20% of the world's unfrozen surface fresh water. With a maximum depth of 1,642 m (5,387 ft), Baikal is the world's deepest lake. It is considered among the world's clearest lakes and is considered the world's oldest lake at 25 million years. It is the seventh-largest lake in the world by surface area. With 23,615.39 km3 (5,700 cu mi) of fresh water, it contains more water than all the North American Great Lakes combined.

Like Lake Tanganyika, Lake Baikal was formed as an ancient rift valley, having the typical long crescent shape with a surface area of 31,722 km2 (12,248 sq mi). Baikal is home to more than 1,700 species of plants and animals, two-thirds of which can be found nowhere else in the world. The lake was declared a UNESCO World Heritage Site in 1996. It is also home to Buryat tribes who reside on the eastern side of Lake Baikal, rearing goats, camels, cattle, and sheep, where the mean temperature varies from a winter minimum of −19 °C (−2 °F) to a summer maximum of 14 °C (57 °F)

We all know, Siberia is extreme cold. These temperatures are so low that Lake Baikal, situated in eastern Siberia and representing the oldest freshwater lake on Earth, and one of the largest and deepest, containing around one-fifth of the world’s freshwater, freezes over. Giant ice blocks, also called ice hummocks, form through movement of ice flow, extreme winds and cold temperatures can reach a height of 15m (50ft). When the lake freezes during the winter, an amazing phenomena takes place: large shards of transparent ice form on the surface of the lake, giving the amazing appearance of turquoise ice.

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 m (5,387 ft). The bottom of the lake is 1,186.5 m (3,893 ft) below sea level, but 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 2 cm (0.79 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 about 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 tributary of the Yenisei. Notable landforms include Cape Ryty on Baikal's northwest coast.

Baikal's age is estimated at 25 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 completely surrounded by mountains. The Baikal Mountains on the north shore and the taiga are technically 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 ones draining directly into Baikal are the Selenga River, the Barguzin River, the Upper Angara River, the Turka River, the Sarma River, and the Snezhnaya River. It is drained through a single outlet, the Angara River.

Despite its great depth, the lake's waters are well-mixed and well-oxygenated throughout the water column, compared to the stratification that occurs in such bodies of water as Lake Tanganyika and the Black Sea.

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