The Kola Superdeep Borehole is the deepest artificial point ever created by humans on Earth. Located in the remote Pechengsky District of Russia’s Kola Peninsula, near the Arctic Circle, the borehole was a Soviet scientific drilling project that began in 1970. Its goal was to penetrate as deeply as possible into the Earth's continental crust to better understand geological processes far below the surface.

By 1989, the deepest branch of the borehole, known as SG-3, reached a staggering depth of 12,262 meters, or about 7.6 miles. This remains the deepest vertical borehole on land to date. Despite this immense depth, it only scratched a fraction of the Earth's crust—less than 0.2% of the distance to the core.

Drilling faced extreme challenges. As the drill went deeper, temperatures reached about 180°C (356°F), nearly twice what scientists had predicted. These high temperatures, along with unexpectedly soft rock formations and intense pressures, made further drilling nearly impossible. The equipment began to fail, and several drill strings broke or became unusable.

The project was eventually abandoned in the early 1990s after the collapse of the Soviet Union, due to both technical obstacles and funding cuts. The borehole was sealed in 1995, and today, the site is deserted, marked only by a rusted metal cap covering what was once humanity’s most ambitious descent into the Earth.

Despite never reaching the Earth's mantle as originally hoped, the project yielded groundbreaking scientific discoveries. It revealed that the geological transition between granite and basalt—long assumed to exist at certain depths—was not clearly present. It also uncovered the surprising existence of liquid water trapped several kilometers below the surface in crystalline rock, as well as high concentrations of hydrogen gas. Perhaps most surprisingly, microscopic fossils of ancient single-celled organisms were found as deep as seven kilometers below the surface, offering clues about Earth’s early biosphere.

The Kola Superdeep Borehole is considered both a remarkable feat of engineering and a symbol of the limits of human exploration within our own planet. It remains a reference point for geologists and engineers studying the deep Earth.

Status & Legacy Today

• The site, now long abandoned, features a rusty metal cap welded over the borehole to seal it off. Nearby towns like Zapolyarny hold repositories for the rock core samples taken during the drilling
• Although surpassed in measured lateral length by oil wells (e.g. in Qatar and Sakhalin), the Kola Borehole remains the deepest vertical borehole ever drilled
• The project was a Cold War-era scientific triumph and continues to inspire new generations of geologists and engineers exploring deep-Earth phenomena.

Scientific Surprises

The Kola Borehole was more than a feat of engineering; it reshaped geological understanding. Key discoveries included:

• No clear granite-to-basalt transition at the expected depth—countering long-held models of crustal layering
• Deep reservoirs of water within crystalline rock, challenging the assumption that such fluids couldn’t exist in the deep crust
• Presence of hydrogen gas and boiling mud emerging from lower levels—unexpected phenomena at those depths
• Ancient microfossils (single-celled marine plankton) dating back around 2 billion years, found approximately 6–7 km below the surface

KeyFacts Energy: Projects Database