The Kola Superdeep Borehole SG-3 is the deepest vertical hole people have ever drilled. It sits on the Kola Peninsula in Russia.
On May 24, 1970, crews started drilling with one clear goal: 15,000 meters down.
Since 1979 the hole has held the world record for vertical depth.
In 1989 it reached 40,230 feet (12,262 meters).
That is deeper than Mount Everest is tall.
The plan looked simple. The bit was supposed to pass from granite into basalt, a denser rock beneath it, and the bottom was supposed to run much cooler than expected.
There was no basalt layer.
Drilling the oldest rock on the peninsula knocked out that granite-basalt model. Water carrying dissolved minerals turned up in the deep rock.
At the bottom the temperature hit 212 °C.
At that heat the rock acts like plastic. It softens, warps the walls, and seals the shaft over and over.
Drilling stopped in 1992. The target was never reached.
How wide is this record?
About 9 inches (23 centimeters) across the main shaft.
Today a rusted steel plate covers the opening.
The depth record still belongs to that hole.
The heat will not yield another foot.
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