Chemists Finally Unravel the Mystery of Siberia’s Explosive Craters

If you need one more reason to worry about warming global temperatures, you can add the ground spontaneously blowing up to the list.

In 2014, a bizarre crater was found in Siberia’s Yamal Peninsula. Since then, several more similar holes have been located. Geologists who studied the sites concluded they were the result of explosions.

Those must have been some blasts, as these are not mere potholes. Some of the craters measure as deep as 165 feet (50 meters). High levels of methane were detected in the regions of the craters, leading scientists to believe the combustible gas—large amounts of which are trapped beneath the Siberian permafrost—was being released as the area’s average temperature rose. But further study established melting permafrost alone wouldn’t have caused the blast.

Now, we finally know what likely happened, thanks to a team of chemical engineers. Publishing their findings in Geophysical Research Letters, the scientists wrote that rapid underground pressure changes played a key role in things going kablooey.

“There are very, very specific conditions that allow for this phenomenon to happen,” said Ana Morgado, a chemical engineer at the University of Cambridge, who worked on the study, in a press release. “We’re talking about a very niche geological space.”

As Morgado and her colleagues began examining the composition of the ground in and around the craters, they realized the explosion wasn’t the result of chemical reactions, and must have had a physical source.

They found their answer in the multilayered ground of the peninsula. At the top is soil that thaws and refreezes as the seasons change. Beneath that lies the permafrost, which, as its name suggests, stays permanently frozen. Beneath those is where things get interesting, and potentially explosive.

During the last ice age, sea waters regressed as glaciers formed. The salt left behind resulted in cryopegs, a geologic layer that doesn’t freeze due to the high levels of salt left behind. In the Yamal Peninsula, the cryopegs are about 3 feet (1 meter) thick, and can be as deep as 165 feet (50 meters) underground. Even deeper underground, below the cryopegs, lies another layer filled with crystalized methane.

For thousands of years, the balance between these layers was maintained, but warmer temperatures have disrupted the cycle. Since the 1980s, water in the topsoil has become more melty, leading it to trickle deeper and deeper into the layers below. Eventually, it began to reach the cryopegs.

The seeping water began to build up, but as it did, it led to pressure increases in the cryopeg. Cracks to the surface began to form, leading to the pressure dropping quickly. All this is happening above the explosive methane, so it’s sort of like playing with matches in a fireworks factory. The gas was released to the surface, and then, KABAM! You’ve got a terrifying new mystery hole in the ground.

Spontaneous explosions of odorless gas are bad. What’s even worse is that methane is a powerful greenhouse gas, which traps way more heat than even CO2. Since the explosions are caused by climate change in the first place, it’s essentially a downward spiral, where heating causes explosions, which in turn causes more heating. It’s not clear how often the crater-forming explosions are happening, and Morgado said the process may be something that occurs “very infrequently.”

So there you go. Climate change is making the very ground we walk on into a powder keg—at least if you live in the Siberian tundra.