The Kola Superdeep Borehole was closed for two reinforcing reasons: the rock at its final depth of 12,262 meters (about 7.6 miles) reached 180°C (356°F), nearly twice what scientists had predicted, making further drilling physically impossible. Then, when the Soviet Union collapsed, the funding disappeared entirely. Drilling stopped in 1992, and the entire facility shut down three years later.
Heat That Broke the Equipment
Soviet scientists originally expected to drill about 14,500 meters deep. They got roughly two-thirds of the way there before the Earth’s interior stopped cooperating. At 12,262 meters, temperatures hit 180°C, almost double what geological models had forecast for that depth. At those temperatures, the surrounding rock became ductile and viscous, behaving more like soft plastic than solid stone. Drill bits deformed. Pipes warped. The rock itself would flow back into the borehole after being cut, making progress nearly impossible.
The temperature spike was dramatic. At shallower depths, conditions had been roughly 100°C, hot but manageable. Over the final kilometers, heat climbed steeply and unpredictably. No drilling technology available at the time, or since, could reliably operate in those conditions for sustained periods.
The Collapse of the Soviet Union
Even if engineers had found a way around the heat problem, money would have stopped them. The Kola Superdeep Borehole was a prestige project of the Soviet state, begun in 1970 as part of a Cold War-era push to explore the deep Earth. When the Soviet Union dissolved in 1991, Russia’s new government had no budget for ambitious scientific drilling. Drilling halted in 1992, and by 1995 the entire research facility was officially decommissioned.
There was no single dramatic shutdown. The project simply ran out of both technical options and financial support at the same time. Without a superpower’s resources behind it, there was no path forward.
What Scientists Found Before It Closed
The borehole may not have reached its target depth, but it produced decades of surprising discoveries. At the boundary where geologists expected to find a clean transition between two types of rock (based on how seismic waves behaved), they instead found intensely fractured rock saturated with hot mineralized water. Finding free-flowing water that deep was completely unexpected. The prevailing assumption had been that rock at those depths would be too compressed and dense to hold water.
Hydrogen gas bubbled up continuously from the well, along with helium, nitrogen, and carbon dioxide. At around ten kilometers down, researchers hit rocks 2.5 billion years old that contained microscopic plankton fossils, evidence of ancient life preserved far deeper than anyone had anticipated. At three kilometers, they found rock remarkably similar to lunar samples brought back by the Apollo missions. At one kilometer, the borehole yielded magnetite, copper, nickel, and water.
These findings reshaped how geologists understood the deep crust. The assumption that seismic boundaries corresponded to neat layers of different rock types turned out to be wrong, at least in this part of the Earth. The boundary was instead a zone of fractured, water-filled rock under enormous pressure.
The “Well to Hell” Hoax
In the 1990s, an audio recording circulated claiming to capture screams rising from the borehole, as if the drill had punctured the roof of hell. Several Christian publications in the United States ran the story as genuine. It was a fabrication. The “infernal” audio turned out to be a mix of sound effects sampled from a 1970s Italian horror film called Baron Blood, blended with recordings of the New York City subway.
What scientists actually recorded from the borehole was far less dramatic but genuinely interesting: a soundscape of echoes, crunches, vibrations, and ultrasonic signals from deep within the Earth’s crust.
What the Site Looks Like Today
The world’s deepest vertical hole is now sealed beneath a rusted iron disc roughly the size of a dinner plate, bolted to the ground on Russia’s Kola Peninsula in the Arctic. The research buildings around it have crumbled into ruins. No scientific work has taken place at the site since the mid-1990s. The borehole itself remains intact underground, but the surface facility has been abandoned for nearly three decades, slowly being reclaimed by the surrounding landscape.
Despite its neglected state, the Kola Superdeep Borehole still holds the record for the deepest vertical hole ever drilled by humans. Other boreholes have surpassed it in total length by drilling at angles, but none have gone deeper straight down into the Earth.