Strangeography

Lake Baikal, Siberia, Russia · · 6 min read

Lake Baikal Should Have Vanished Millions of Years Ago. Instead, It's Getting Deeper

Most lakes fill with mud and disappear. Siberia's Lake Baikal has lasted about 25 million years, and the reason lies miles beneath its floor.

Lakes are supposed to die. Siberia’s Lake Baikal has been around for something like 25 million years, and instead of filling up with mud, it’s getting deeper. The reason is hidden miles beneath the ice.

A lake that refuses to die

A lake’s life usually follows a simple script. It forms, rivers slowly fill it with mud, and after thousands to tens of thousands of years it becomes a swamp. Then a meadow. Then nothing.

Baikal never followed that script. And it holds other oddities: seals living more than 1,200 miles from the ocean, a see-through fish that’s almost 40% oil, and oxygen all the way to the bottom.

Meet Lake Baikal

Lake Baikal sits in southern Siberia, Russia. From space, it looks like a giant blue crescent carved into the forest. It’s almost 400 miles long, about the length of a drive from Los Angeles to San Francisco.

It’s also deep. At its deepest point, it reaches more than 5,300 feet. Stack three Empire State Buildings on top of each other, and the top one would still be underwater. No lake on the planet is deeper.

All that depth means Baikal holds more water than all five of North America’s Great Lakes combined. That’s roughly one-fifth of all the unfrozen fresh water on Earth’s surface, in a single lake.

More than 300 rivers pour into it, and only one, the Angara, flows out. The water is so clear that on a good day you can see nearly 100 feet below the surface.

Why lakes are supposed to disappear

Think of a lake as a giant bathtub. Every river flowing in brings sand, mud and bits of dead plants. All of it sinks to the bottom. Year after year, the tub fills with dirt instead of water.

That’s why most lakes are geological babies. Many of the lakes in North America and Europe formed only when the glaciers of the last ice age melted, around 10,000 to 20,000 years ago.

Baikal is about 25 million years old. Humans have been around for about 300,000 years, so this lake is roughly 80 times older than our entire species.

That left scientists with two puzzles. How has Baikal survived this long without filling up? And what are seals doing in the middle of Siberia?

The crack under the lake

The answer to the first puzzle has nothing to do with water. Baikal isn’t sitting in an ordinary dip in the ground. It sits inside a rift, a giant crack in Earth’s crust where the land is slowly being pulled apart.

Picture grabbing a warm slice of pizza by both ends and gently pulling. The cheese in the middle stretches, thins and sags. That’s roughly what’s happening to the crust under Baikal. As the two sides drift apart, the middle keeps sinking.

GPS stations around the region suggest the sides are separating by about a fifth of an inch a year. That’s slower than your fingernails grow, but over a few million years it adds up.

Here’s the surprise: the mud is there after all. Under the lake floor lies a layer of sediment roughly four miles thick. That puts the true bottom of the crack somewhere around five to seven miles below the surface. Mount Everest is about five and a half miles tall. Baikal’s rift is thought to be the deepest continental rift on the planet.

Baikal has been filling with mud all along. Its floor just keeps sinking faster than the mud can bury it. Without that endless sinking, Baikal would have become a swampy valley millions of years ago.

The night the land sank

Sometimes the sinking is sudden. In January 1862, an earthquake estimated at around magnitude 7.5 struck near Baikal’s eastern shore. Roughly 80 square miles of flat land, pastures and villages included, suddenly dropped by up to 25 feet. The lake poured in.

Homes, fields and nearly all the livestock disappeared under the water. Most families had boats and rowed to a nearby hill. Today the spot is a bay called Proval, which roughly means “the collapse.”

The crack isn’t finished. Some geologists think that if it keeps widening for millions more years, Baikal could become the start of a new ocean, much like what’s happening in East Africa today.

Seals 1,200 miles from the ocean

The second puzzle swims in the lake. The nerpa, or Baikal seal, is one of the smallest true seals in the world and the only seal species that lives entirely in fresh water. Around 100,000 of them live in Baikal.

That’s true at the species level. A few populations of other seals also live in fresh water, including two ringed seal subspecies in Lakes Saimaa and Ladoga and the Ungava and Iliamna populations.

The problem is distance. Baikal is more than 1,200 miles from the Arctic Ocean, and seals aren’t built for long hikes.

The nerpa’s closest relatives are ringed seals from the Arctic, and it keeps Arctic habits. Its pups are born on the ice with fluffy white fur. In winter, adults keep breathing holes open by scratching at the ice with their claws.

The leading theory reaches back to the ice ages. Massive glaciers blocked rivers across Siberia and created giant lakes along the edges of the ice. Scientists think the nerpa’s ancestors may have swum up from the Arctic along rivers like the Yenisei and the Angara, using those glacial lakes as stepping stones.

Then the ice melted, the stepping stones disappeared and the seals were stuck. Exactly when this happened is still debated. Estimates range from a few hundred thousand to a couple of million years ago.

Life all the way to the bottom

In most very deep lakes, the bottom is nearly lifeless. Lake Tanganyika in Africa is another rift lake, almost as deep as Baikal, but below a few hundred feet it has barely any oxygen.

Baikal has oxygen all the way down, more than a mile deep, so life can survive at every level. Scientists have counted more than 2,600 animal species in the lake, and more than half live nowhere else on Earth.

Three things make this possible. The first is a cold-water elevator. About twice a year, huge masses of icy surface water become just heavy enough to sink, and they keep going until they reach the bottom. They carry fresh oxygen down with them.

The second is a tiny cleaning crew. A crustacean called Epischura, smaller than a grain of rice, makes up most of the lake’s animal plankton. It spends its life grazing on algae and bacteria, which is a big part of why the water stays so clear.

The third is the golomyanka, or Baikal oilfish. It has no scales, it’s almost see-through, and in adults up to around 40% of its body is oil. It has no swim bladder, the air pocket most fish use to float; the oil keeps it buoyant instead. That lets it range from near the surface down to around 5,000 feet. Instead of laying eggs, it gives birth to live young, potentially thousands at a time.

Locals say a golomyanka that washes up in the sun melts until only oil and bones remain. That’s probably an exaggeration. The fish is also the seals’ main food.

The modern threat

A lake that survived 25 million years of earthquakes, ice ages and a continent tearing apart might seem indestructible. It isn’t.

Over the past couple of decades, near some shoreline towns, thick mats of green algae have piled up on beaches and on the lake floor. Researchers blame wastewater from towns without proper sewage treatment, especially phosphates from detergents, which act like fertilizer for algae.

Some of Baikal’s ancient sponges, which once formed bright green underwater forests, have been turning brown and dying. And the omul, a fish found only in Baikal, declined so much that Russia banned commercial fishing for it in 2017.

The takeaway

The lake that outlasted 25 million years of geological chaos is now struggling with soap.

That’s also the hopeful part. Unlike a magnitude 7.5 earthquake, pollution is something people can fix, and scientists already know where much of the trouble comes from.

Sources

#lakes#geology#rifts#seals#siberia

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