How Deep is the Deepest Hole in the World?

A portal to the center of the eary sits among the ruins of an abandoned project site in Murmansk, Russia, not far from the Norwegian border. Sure, it's covered and welded shut, but it still sounds like a horror film to me. The deepest hole ever dug may be pretty unassuming, but I suspect I'm not alone in being a little freaked out by it. An internet search about the wordl's deepest hole turns up the suggestion "Kola Superdeep Borehole screams." No wonder locals call it the well to hell.

Before the very idea of a superdeep hole starts haunting your dreams, keep this in mind—the hole is only nine inches in diameter (that's about 23 centimeters). There's no way you could fall into it.

How deep is the deepest hole?

Known as the Kola Superdeep Borehole, the deepest hole ever dug reaches approximately 7.5 miles below the Earth’s surface (or 12,262 kilometers), a depth that took about 20 years to reach. 

The hole was intended to go “as deep as possible,” which researches expected to be around 9 miles (that’s ~14,500 meters). But the scientists and engineers were forced to give up when they hit unexpectedly high temperatures. At 7.5 miles below the surface, the 2.7 billion year old rocks twere at temperatures of around 180 degrees Celsius (or a scorching 356 degrees Fahrenheit). This was almost twice as hot as they'd predicted.

The Russian scientists in Kola described the rocks at those depths as behaving more like plastic than rock.

Such high temperatures deform the drill bits and pipes. The rocks themselves also become more malleable. The Russian scientists in Kola described the rocks at those depths as behaving more like plastic than rock. 

Since the drilling was stopped in 1992, and the project site was abandoned around a decade later, the Kola Superdeep Borehole has maintained the record for the deepest artificial point on Earth. Humans have since dug longer boreholes, including the 12,289-meter borehole drilled in the Al Shaheen Oil Field in Qatar and the 12,345-meter offshore oil well near the Russian island of Sakhalin. But the hole in Kola remains the deepest.

Why do we dig deep holes?

There are a few reasons we humans dig deep into the Earth—extracting resources like fossil fuels and metals, for starters. A 100-year-old ...

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