Past eight in the evening on the last day of August, after a ten-hour climb, we haul ourselves to the high rim of the Baikal Canyon. From where we stand, high plateaus, in hard, clear light, seem to stretch forever westward to the Urals. Facing east, my companion, the huge Siberian woodsman Semyon Ustinov, spreads his long arms. Far below, his beloved Baikal, the most ancient lake on earth, is shrouded in mist that drifts up the steep talus slope as if in search of us. The canyon rim on which we stand is a mile or more above the surface of the lake, whose greatest depth is 6,300 feet, or 1.2 miles, with an additional four miles of sediment above the bedrock. The great Baikal rift is seven times as deep as the Grand Canyon, by far the deepest land depression on the planet.
For the past week we have been exploring Lake Baikal and talking about the threats to its ecology with a group including Semyon and his friend the controversial writer Valentin Rasputin. The lake, which lies in a great crescent nearly four hundred miles long, fills a widening valley where two tectonic plates, pulling apart, drop the depression ever lower. This vast plateau north and west of Baikal, known to geologists as the Siberian Platform, is being separated from Asia to the south and east by this shift in the earth’s crust. Because the fault’s floor is widening about one inch every year, Baikal can collect new sediment without any loss to its huge volume of water. Although its surface is more or less the size of Lake Superior, Baikal holds nearly the equivalent of all five of the Great Lakes, or about one fifth of all the fresh water on earth. (This astonishing volume might be better understood another way: if all of Baikal’s 334 tributaries were diverted, and its sole outlet, the Angara River, were to drain it, the emptying would take four hundred years. The Amazon, Ganges, Mississippi, Nile, and Congo, together with all the other rivers and streams on earth, would have to flow a year or more just to refill it.)
Because the rift grows ever larger, the four miles of lake floor contains matter that has accumulated for twenty to thirty million years. (Lake Tanganyika, in Africa’s Western Rift Valley, which looks like a miniature Baikal even in its distinctive crescent shape, is the earth’s second oldest lake—two million years—and second deepest, at 4,700 feet.) Even the largest of ordinary lakes may live at most 50,000 years before they fill with silt, evaporate, and die, and, by this criterion, “The Blue Pearl of Siberia” is all but eternal. It is often called an inland sea—“Ye glorious sea, ye sacred Baikal” goes an old Siberian song—or even, like the Red Sea, an incipient ocean. Hydrothermal vents in the lake floor at Frolihka Bay, in the northeast—the first such vents ever located in fresh water—support rich communities of bottom…
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