Lake Baikal (October 1999), from the OrbView-2 satellite.
Lake Baikal is a rift lake in southern Siberia, between Irkutsk Oblast to the north-west and Buryatia to the south-east. It formed as an ancient rift valley about 25 – 30 million years ago, hence its long crescent shape.
With 22 – 23% of the world's surface freshwater, Lake Baikal is the largest freshwater lake in the world, in terms of volume. It is also the oldest and deepest lake in the world, and the 7th-largest lake in terms of surface area. It contains more water than the North American Great Lakes combined.
Several rivers flow directly into Lake Baikal, but it is drained only by the lower Angara River, which flows northwards from the lake's south-western shore to join the Yenisei River.
Below the lake is the Baikal Rift Zone. At 8 – 11km below the surface, it is the world's deepest continental rift. About 7km of sediment rests on the rift floor, so the lake bottom is just over 1km below sea level.
The fault zone is seismically active, with hot springs in the region, and earthquakes every few years. The rift itself is active, and widens about 2cm a year.