Lake Baikal. Geological History

Lake Baikal is a large lake located in eastern Siberia in the Buriat Autonomous Republic and Irkutsk Oblast (Province) of the Russian Federation. Its name is believed to be derived from the Turkic bai (rich) and kul' (lake). With its 23,000 cubic kilometers of volume Lake Baikal contains 90 percent of the former USSR's and 20 percent of the world's freshwater.

That is as much water as in all of the North American Great Lakes combined. That enormous volume is a consequence of the great depth of the lake; its average depth is 730 meters, with a deepest point of 1,637 meters. The lake's surface lies 455 meters above sea level. Largely oriented north to south with a crescent-shaped length of 636 kilometers and an average width of just 48 kilometers, Baikal has a surface area of a comparatively modest 31,468 square kilometers, but the flush time, the time it takes to replace all the water in a lake or resevoir, for the lake's 23,000 cubic kilometers is four hundred years.

After construction of the Bratsk Dam in 1961 on the Angara River, the lake's only outlet, the average level of the lake rose 1 meter, and the lake surface increased by 500 square kilometers. A virtual inland sea, Baikal has 174 capes and 6 major bays or gulfs. Fed by 336 streams, the lake's water is very clear, with visibility up to 40 meters beneath the surface; this is a result of its low mineral content. The lake freezes over from December to May with an ice crust 70-115 centimeters thick, and ice floes may persist into June.

Geological History. Nineteenth-century scientists theorized that Baikal was once a fjord of the Arctic Ocean or even the easternmost part of an ancient Pontic-Sarmatian sea stretching across the West Siberian Plain and Kyrgyz Steppe. Other scientists linked Baikal to the Pacific Ocean or to the Jurassic Sea, which once covered Mongolia. However, geologists and paleontologists rejected the idea of a relict (a relief feature remaining after other features have disappeared) ocean for lack of mineral and fossil evidence.

The most widely accepted theory today is that the lake originated 25 million years ago in a process much like that which created the world's other rift systems. The roots of the lake basin extend to the Earth's upper mantle, about 50 kilometers deep. Below this basin exists an anomalously hot portion of the Earth's core.

Light, superheated plasma rose from the core and in places punctured the crust of the Earth, lifting the crust above it to create the mountain ranges that bracket Baikal. At the same time this plasma flowed under the crust to the sides, creating horizontally fissiparous (divisive) forces that widened the rift made by the initial eruption while uncovering previous rifts down to the upper mantle and creating huge new ones and intermontane (between-mountains) abysses.

When the crust cooled, the lake basin, with three principal depressions, was formed and filled with both water and sediment. Lake Khubsugul, which is just across the border in Mongolia and is the source of the Selenga River, Baikal's most important tributary, is another rift valley lake.