Deepest Freshwater Lake in the World

How did Lake Baikal form and what makes it so important to science?

In a southern region of Siberia near the border of Mongolia is Lake Baikal, not just the most ancient lake in the world at 25 million years old, but the deepest too. To be precise it is 1,642 metres (5,387 feet) at its deepest point, which is deep enough to stand five Eiffel Towers (each 324 metres/1,063 feet) on top of one another and for the top-most tower to still not break the surface.

Because of its great age, we can’t be certain of how Lake Baikal formed, unlike many inland seas and lakes that can usually be attributed to the movement of glaciers during previous ice ages. However, it’s suspected that the body of water was originally a river bed during the Palaeogene epoch. Over millions of years it formed several shallower and narrower lakes that were connected by rivers during the Pliocene epoch, before the lakes gradually joined to become one -still in the Pliocene, while plate movement created the deep basin. Today Lake Baikal contains an astonishing 20 per cent of the world’s unfrozen fresh water, which is still very pure despite pollution from a coastal paper mill and where the Selenga River feeds into the lake.

It’s also one of the most biodiverse lakes on the planet with 1,340 species of animal and 570 species of plant – nearly half of which are endemic to the lake ecology. Coupled with its natural beauty, this is why Baikal was made a UNESCO World Heritage Site in 1996.

Baikal’s underwater neutrino telescope

Floating near the bottom of Lake Baikal is a telescope called the NT-200. It’s not looking at stars and galaxies, and neither is it studying the strange life on the lake bed. NT-200 is actually pointing towards the Earth’s core and trying to find a neutrino: a particle with no charge that only has a very weak interaction with matter, so it can pass straight through any material, including the Earth, without hitting anything.

Russian scientists are trying to find the elusive high-energy neutrino released by gamma-ray bursts and their ilk, but there’s too much noise created by relatively common low-energy neutrinos caused when cosmic rays hit the Earth’s atmosphere. To screen most of them out, the 42 x 70-metre (140 x 230-foot) NT-200 telescope has been placed a kilometre (0.6 miles) down in the depths of Lake Baikal.

Ancient depths

Though the present bottom of Lake Baikal is nearly 1,700 metres (5,600 feet) down, the depth of the fissure it sits in is deeper. Much deeper in fact: it’s estimated that to reach the bedrock at the deepest part you’d have to dig through around eight kilometres (five miles) of sediment, making the Lake Baikal trench nearly as far down as the Mariana Trench (ie 11 kilometres/6.8 miles) – the deepest oceanic trench in the world.

The sediments have collected over millions of years, the oldest of which at the base of the trench began stacking up when South America and North America were yet to form a land bridge and the Earth’s climate was considerably warmer.

How Lake Baikal measures up? Incredibly, the bottom of the deepest part of the rift Lake Baikal sits in is nearly 8,000m (26,247ft) below the base of the lake bed.