In northeast Siberia, there’s a hole so massive it’s been nicknamed the Doorway to the Underworld.

As of 2023, it’s about 88 hectares big, or  a little less than one square kilometer. But here’s the thing: since  it appeared in the 1960s, that doorway has been growing,  releasing tons of greenhouse gasses into the atmosphere and  pollutants into the local river.

Which, ya know, sounds pretty bad, and it is. But while some researchers dread the consequences of this doorway opening up,  others have found a silver lining. Because as it turns out, there's  something useful in the Underworld. [♪ INTRO] The Doorway to the Underworld  goes by several other names, from the innocuous “cave-in”,  to the much more scientific but no less catchy “retrogressive thaw megaslump”.

It is, in fact, the most  mega megaslump in the world… by which I mean it’s the largest. But the Doorway to the Underworld  is most often called the Batagay or Batagaika Crater, because it is  located near a small town called Batagay. And with the name “crater”, you  might think that it was created by a massive asteroid impact or  something similar falling from space.

But you’ve seen this thing. Like, we’ve showed it to you. The hole is vaguely shaped  like a stingray or a tadpole, measuring 2700 meters long from head  to tail, and 990 meters at its widest.

And that wonky shape suggests  it was created by something other than a giant space hamster missing  its belly flop into the Arctic Ocean. The creator of this megaslump is, in fact, us. See, the terrain in this area  is basically the biggest, but worst tasting, ice  cream cake you’ve ever seen.

It’s made of several layers of permafrost, which is like really wet land that’s been  continuously frozen for at least 2 years. And before the crater formed,  those layers added up to something around 75 meters thick. There’s a bedrock base at the bottom, and then alternating layers of stuff that’s either  a bit more icy or a bit more sandy.

And the sandy layers have layers inside  of them, too, made of woody material, peat, and other biomass like  pollen and insect remains. Delicious! Om nom nom.

Geologists hypothesize that this cake  was assembled over thousands of years. As the permafrost formed, sand was getting  blown over from a nearby floodplain. But because of those alternating layers, we know this wasn’t happening consistently.

The region must have gone  through cycles of freezing and relative warming…during which time you’d get stuff like meadows and coniferous forests growing. Now before the Crater formed, you could expect to see some amount of seasonal melting. But if the upper layers of a  permafrost cake melt too much, it could initiate a dangerous feedback loop.

For example, higher surface  temperature might cause the snow that’s covering the upper permafrost layers to melt. And without the snow to reflect the Sun’s  toasty light back into space, the darker, newly-exposed layers would absorb more  light and start to thaw themselves. And once a layer of permafrost has  done a bit more thawing than usual, it’s much more likely to continue  doing so in subsequent years.

But that’s not all. These warmer  temperatures also wake up bacteria in the ground that have been  hanging out in what’s basically a non-SciFi version of suspended animation. Then, they get to work decomposing  organic material in the permafrost, producing greenhouse gasses as byproducts.

And when the permafrost melts  and collapses, those gasses are released into the atmosphere…making  things warm up even faster. Now, typically, melted permafrost will  form massive puddles on the surface. But the region that Batagay Crater calls  home isn’t sitting at one single elevation.

The “tail” part is much lower, so when  all that ice melts, the water and eroded sediments can drain into the nearest  river…leaving a massive hole behind. Thanks to Brilliant for  supporting this SciShow video! Brilliant is an online learning platform with thousands of lessons in computer  science, math, and science.

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Plus, you’ll get your first 30 days But how old is that hole? Like if you could time travel back to the 1960s, you’d find yourself standing  in a seemingly harmless ravine. But the Soviets had recently  cleared a nearby forest to search for good places to mine  a bunch of different minerals.

Without tree roots, the landscape  became more susceptible to erosion. And without tree cover, it was a lot  easier for the Sun to warm the ground. In other words, the sudden  lack of trees kicked off a vicious cycle of permafrost melting.

We actually have satellite images  that show the ravine gradually expanding over the decades, taking  on its stingray-slash-tadpole shape. And by 1991, it had grown so large that scientists could officially call it a megaslump. And it’s kind of shocking  how quickly the slump has grown in just the past few decades.

Like between 2019 and 2023, the edge of  the crater’s bowl retreated by 53 meters, at an average rate of around 12 meters per year. Since 1991, Batagay Crater has lost an estimated 35 million cubic meters of matter. Two-thirds of that has been meltwater,  with the rest being a mix of sand and biomass that was layered  throughout the permafrost.

Each year, the melted permafrost also releases 4,000 to 5000 tons of previously  sequestered organic carbon. But the growing megaslump isn’t  just creating environmental problems by releasing a bunch of CO2  and methane into the air. The runoff has also made the river  water unsuitable for drinking, affecting the residents in Batagay and clogging the waterway down to the sea it drains into.

Unfortunately, there is nothing  we can immediately do to stop Batagay Crater’s growth, but it might  stop expanding on its own within just a few decades, because the situation  is literally about to hit rock bottom. Below and at its sides, the  crater is about to hit bedrock. It’s running out of permafrost to melt.

But all that melting permafrost is actually  a good thing in one particular way. Basically, the Batagay Crater is  self-excavating, and each year it reveals new, well-defined cross-sections  of its geological history. At the head of the proverbial stingray,  there’s a sheer cliff that’s 55 meters tall, perfectly exposing the permafrost’s layers.

Geologists can sample the ice  structure, sediment composition, and biomass remains from each  layer of the permafrost cake, and compile a history of the region  that stretches back 650,000 years. They’ve even discovered animal  remains…from the remnants of ants and mushroom-inhabiting beetles,  to bones from much more charismatic fauna like cave lions, wooly mammoths, and bison. And in 2018, one team found a  roughly 40,000-year old foal that was so well-preserved by the icy permafrost,  it still had hair and muscle!

Meanwhile, a different study found lemming remains that researchers estimated to  be around 330,000 years old! As Batagay Crater grows, scientists can paint an ever-more detailed picture of the past. And if you want in on that action, you  could dedicate your life to earth science and join one of the teams that  regularly samples the Crater’s walls!

The Institute of Applied Ecology of the North organizes scientific expeditions to the Crater. You just gotta watch out for  all the animals in the region that are still very much  alive…like bears, mosquitos, and all those ancient microorganisms  that have just woken up! [♪ OUTRO]