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 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 (0.8 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 25–30 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 completely surrounded by mountains. The Baikal Mountains on the north shore, the Barguzin Range on the northeastern 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.
Lake Baikal's water is very clear
Baikal is one of the clearest lakes in the world. During the winter in open sections the water transparency can be as much as 30–40 m (98–131 ft), but during the summer it is typically 5–8 m (16–26 ft). Baikal is rich in oxygen, even in deep sections, which separates it from the 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 4–5 months; from early January to May–June (latest in the north), the entire 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 up by the sun, and in May–June, the upper circa 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 very 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 where the lake is covered by ice. At some locations, hydrothermal vents with water that can be 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 very little effect on the lake's temperature because of its huge volume.
Stormy weather on the lake is common, especially during the summer and fall, and can result in waves as high as 4.5 m (15 ft).
Lake Baikal as seen from the OrbView-2 satellite
Spring ice melt underway on Lake Baikal, on 4 May: Notice the ice-covered north, while much of the south already is ice-free.
Circle of thin ice, diameter of 4.4 km (2.7 mi) at the lake's southern tip, probably caused by convection