The Soviets Drilled the Deepest Hole Ever. What on Earth for?

 

In the late 1980s, from certain corners of cable TV, you could learn that the Soviet Union had dug straight to Hell. Not in the metaphorical, Reagan-Era, “look what those commies have done” sense of the word. No. They had literally dug straight to Hades.

The story ran on a program called Praise the Lord, the long-running worship and current events program aired by the evangelical Trinity Broadcasting Network, which reached around 5 million daily viewers. Over several episodes, the program explored how a Soviet deep drilling project had accidentally tunneled into Satan’s underworld.

When the Soviets lowered a remarkably heat-resistant microphone into an underground cavern discovered by their dig, so the story went, the Russians—to their horror and surprise—recorded the wailing of damned souls as they languished in temperatures exceeding 1,800 degrees Fahrenheit. 

Their lamentations were played on the air for a stunned audience. In later developments, the network reported that a winged, bat-like figure had been seen rising from the hole and blazing a trail across the Siberian sky.  This was all the proof they needed to assert that, out there somewhere in the Siberian tundra laid the “Well to Hell.”

Then the story began to unravel. First, the Soviet drilling project in question was actually taking place hundreds of miles to the west of Siberia along the border with Norway on Russia’s Kola Peninsula. 

Next, the recordings of doomed sinners voicing their eternal misery turned out to be just a sound loop from a 1972 b-movie horror flick called Baron Blood. Then a Norwegian teacher came forward to say he’d planted the story about the winged demon just to see how gullible the producers of Praise the Lord really were.

Nevertheless, the myth has since migrated from Christian cable TV to credulous quarters on the internet where, on YouTube and TikTok, you can still encounter that same recording as proof of the everlasting inferno beneath the Siberian tundra.

In fact, the Soviets really did drill a very, very deep hole—by 1979, the deepest on Earth. Today, with a little effort, you can walk right up to the actual hole the evangelicals called the Well to Hell. Alas, it's really called the Kola Superdeep Borehole, part of a Soviet science program. You can stand right at the edge, but there’s no danger of falling in. 

It’s far too narrow for that. It’s also plugged up. Since 2008, the very slender chasm has been bolted shut with a dinner-plate-sized steel cover that measures only about 9 inches across. But the hole it hides plunges down for more than 40,000 feet into the earth and took more than 20 years to dig. That’s deeper than the altitude at which most commercial airlines fly and deeper by about 20,000 feet than any other hole anywhere else on Earth.

The deepest hole on Earth. That sounds pretty stupid as far as scientific projects go—sort of like the abiding sandbox fantasy so many American kids have of digging clear through the planet to the other side, from say, Michigan or Texas or Montana, all the way to China.

But whereas the Well to Hell revelation turned out to be nothing more than a hoax, the real Kola project actually delivered something sublime: a radical new understanding of the center of the Earth. Unlike the tortured voices on that cable-access tape, what the drill recorded needed no embellishment.

The team of scientists who plotted the dig for a decade before the project launched had real ambitions: They hoped to bore through the continental crust and reach the Mohorovičić discontinuity—the boundary separating Earth’s crust from the mantle below. Crossing it would give scientists their first direct look at the vast layer that drives plate tectonics, feeds volcanoes, and ultimately shapes the continents.

The dig was, in a sense, a mirror of the space race. If Sputnik and Gagarin proved Soviet superiority in the heavens, an ambitious drilling project into the bowels of the planet meant the Soviets could reign in the underworld, too. The date the Soviets chose to formally begin the first round of drilling was May 24, 1970, the 100th anniversary of Lenin’s birth. The project was tied to the Soviet Union’s own founding myth.

Step Right Up!: The Kola Superdeep Borehole is 40,000 feet deep, the deepest human-made hole on Earth, but it doesn’t look like much from the surface. Today it’s plugged up with a 9-inch steel plate, surrounded by debris, and blends into the landscape. Credit: Rakot13 / Wikimedia Commons.

“We had promised [Nikita] Khrushchev we’d dig to 15,000 meters (49,213 feet)—a good round number,” Sergei Nestrenko, who was then a young drilling engineer at the Kola Superdeep Borehole, told me by phone from his home in Murmansk.

But they never did get where they were going. They didn’t even really come close.  Even at 40,230 feet, the deepest point humanity has ever drilled, the Kola borehole had penetrated barely a third of the way through the continental crust beneath northern Europe.

By most practical measures, you could say the Kola Superdeep Borehole failed. But that failure transformed the way geologists view our subterranean world. Until then, scientists understood the deep continental crust largely through indirect evidence. 

They bounced seismic waves through the Earth and measured subtle variations in gravity and magnetism, then inferred what kinds of rocks must lie below. It was a successful method—except where it wasn’t.

“Think of these methods like you think of an ultrasound,” Ulrich Harms told me when we spoke recently. “You can see your kidneys in great resolution. But if no one had ever dissected a body beforehand, you wouldn’t know that’s a kidney.”

Harms, a geologist and drilling engineer who first visited the Kola site in 1984, would go on to help lead many of the world’s largest scientific drilling projects through Germany’s International Continental Scientific Drilling Program. Kola, he said, became one of the first opportunities to compare the seismic models to the real thing. The real thing, he said, offered some wild stuff.

Perhaps the biggest surprise was what the drill never encountered. For decades, geologists had interpreted a prominent seismic boundary deep beneath the continents as the transition from granite to basalt—the dense volcanic rock that forms most of the ocean floor. 

But Kola never hit basalt. The supposed boundary was nowhere to be found. Instead, the drill continued through more granitic and metamorphic rock, showing that the seismic boundary did not mark a change in rock type at all. It marked a change in how the same rocks behaved under immense pressure and temperature.

Other discoveries proved just as momentous. Nearly 22,000 feet beneath the surface, drill cores contained microscopic fossils from two dozen species of plankton that had drifted through an ancient sea more than 2 billion years ago. 

This showed that even after billions of years of burial deep within the continental crust, unmistakable evidence of some of Earth’s earliest life had survived. Between 16,000 and 23,000 feet, the borehole encountered saline water circulating through fractures in crystalline rocks that geologists had long considered essentially dry. 

Rather than groundwater that had somehow seeped miles underground, the fluids appear to have originated within the crust itself. As ancient minerals were transformed by heat and pressure, they released chemically bound water, while reactions between water and iron-rich rocks generated hydrogen gas, showing that the supposedly inert continental crust was still chemically active billions of years after it had formed.

“Taken together, this all revealed that the deep crust wasn’t dry and inactive,” Harms told me. “Instead, it was a dynamic place where ancient life, water, and chemical reactions continued to exist and interact billions of years after the rocks themselves had formed.”

Just as the world began paying attention, the Soviets almost lost the whole project. In August of 1984, Moscow hosted one of the largest scientific meetings ever held, and for the first time the Soviet Union invited foreign researchers to see its deepest drilling project firsthand. 

This was the 27th International Geological Congress, a gathering of nearly 5,700 geologists from 110 countries. By then, the Kola borehole had already reached 39,521 feet, farther beneath the Earth’s surface than anyone had ever drilled. Harms was among the visitors. “It was extraordinary,” he told me. “Nothing else in the world came close. They were doing really pioneering work.”

Super Deep True Drilling Story: The remains of a 27-story tower built for the Kola Superdeep Borehole project. The tower was meant to protect heavy machinery, crews, and laboratories used for sample analysis from the extreme weather of Kola Peninsula in the Arctic Circle. Credit: Andre Belozeroff / Wikimedia Commons.

For a brief moment, the Soviet Union stood unambiguously at the forefront of one of science’s most ambitious engineering enterprises. The Americans had abandoned their own deep drilling Project Mohole nearly two decades earlier—at a mere 601 feet—after cost overruns and management disputes, while Germany’s own five-and-a-half-mile deep KTB borehole was still years away. 

Whatever else could be said about the Soviet system during the twilight years of the Brezhnev stagnation, it had succeeded in drilling deeper into the Earth than anyone had thought possible.

Then, only days after the geology Congress ended, catastrophe struck. On Sept. 27, 1984, as drilling resumed, roughly 3 miles of aluminum cylinders, at the end of which spun the drill bit, twisted off and became irretrievably lodged deep underground. Years of painstaking progress vanished in a clank of metal. “At least it happened after everyone went home,” said Nestrenko. “But there wasn’t any question of giving up.”

Nestrenko said the engineers had no choice but to abandon the broken section, back the drill up to roughly 23,000 feet, and begin drilling again along a new branch. It would take another five years before they regained the depth they had already reached.

By the early 1990s, the Kola borehole project was nearing its end. The hole extended to such a depth that the Earth had stopped behaving like Earth. At roughly 40,000 feet, temperatures climbed to nearly 356 degrees Fahrenheit—almost twice what geologists had predicted before drilling began. The immense heat, combined with the crushing pressure of the overlying crust, transformed the ancient crystalline rock into something more akin to molasses.

“It was like a flow in the ancient granite,” Nestrenko told me. “Like stiff plastic.”

To anyone who thought they knew granite, that sounded ridiculous. Granite is supposed to fracture. Hit it with enough force and it breaks into chips that a drill can carry away. But nearly 8 miles beneath the Kola Peninsula, the rock had crossed some bizarre invisible threshold. 

Instead of shattering, it slowly deformed. As soon as the drill bit passed, Nestrenko explained, the surrounding granite began creeping back toward the borehole, squeezing the shaft shut almost as quickly as the engineers could deepen it. Every trip to replace a worn drill bit gave the Earth another opportunity to reclaim the hole they had just created.

“It would pinch the hole closed,” Nestrenko recalled. “When we pulled the drill string back, the rock flowed inward.” The engineers had reached the limits of drilling. The rock simply no longer behaved like rock.

Then in 1991, the Soviet Union dissolved, taking with it the financial and symbolic backing needed to build new drills or find novel solutions. The newly formed Russian government, stumbling awkwardly into economic collapse, called off drilling in 1992. The broader research program wound down over the following years, with the site formally mothballed in 2008 and left to decay.

When I drove through the area about 10 years ago, it appeared as though the 700 or so geologists, engineers, drilling technicians, and others who worked at the dig had one day risen from their lab benches and just walked away. 

There’s little reason to think much has changed since. The sliver of highway between Murmansk and the Norwegian border along which the remnants of the borehole reside are as remote and desolate a wasteland as you could hope to find. A low-slung pair of warehouse-like laboratories have been ground down by the arctic winds.

Only the tower housing the old drilling column had been dismantled. The rest of the site sits like a ransacked museum, frozen as it was left, vulnerable to metal and wire scavengers.  In contrast to the other secretive relics of the Cold War that surround it—the ones you can get arrested for trying to find—it’s almost as if the Russians didn’t see their hole as a secret worth guarding.

When I stood at the edge of this giant Arctic ghost town, the whole project seemed to me to be less a question of engineering and practicality than a question of minds at play.

The children in the sandbox never make it to China—any more than the Soviets were going to reach the Earth’s mantle. But the measure of the Kola Superdeep Borehole turned out to have little to do with the goal that justified the effort.

Instead, the Kola Superdeep Borehole overturned decades of geological assumptions. It showed that the continental crust was hotter, wetter, and more chemically active than scientists had imagined. It also revealed that one of geology’s most trusted road maps was leading us astray. Along the way, it pushed drilling technology to limits that engineers still regard with admiration. None of those discoveries had been the point.

That might be the value of asking a big, stupid question. The ones that seem most sensible often just confirm what we already know. The ones that are childishly fanciful can force us to discover where we’re wrong and forge new paths forward into the dark. 

-Charles Digges, Nautilus 

And yes, his name was Digges!