Kola Superdeep Borehole: someone painted the wrong depth on its lid

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The lid

A rusty hatch, twelve massive bolts, ruins all around. Beside it, a lake whose Sami name means Lake under Wolf Mountain. In a 2016 photo the lid has a painted depth: 12,226 metres. That is wrong. The correct depth is 12,262.

Go down and check. Keep scrolling.

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"Start!"

On 24 May 1970, on a standard production rig, the order came as routine: "Start!" Holes like this were planned to reach 15 kilometres. The aim was to see a section of the crust down to the "basaltic" layer, known only from seismic readings.

330 m

The Eiffel Tower

Stand it on its tip at the wellhead and the tower ends here.

828 m

Burj Khalifa

The tallest building in the world has run out. From 800 metres down, the water in the rock is salty, and it gets saltier.

1,100 m

The mud gives off gas

Here the drilling mud starts releasing dissolved gas by itself. It will do so in places down to 4,570 metres.

1,665 m

Ore nobody knew about

Down to 1,830 metres runs commercial copper-nickel ore that nobody knew about at the surface. The chief geologist said finding it alone justified the cost of the rig.

2,200 m

The deepest cave

The deepest known cave ends about here, at around 2.2 kilometres. The drill bit, by the way, is only 214 millimetres across, narrower than a dinner plate.

3,000 m

Three kilometres

Hydrogen now predominates in the gas. Temperature still matches the calculation, a degree per 100 metres. Below this it climbs two and a half times as fast.

Remember this depth. It comes back.

4,000 m

The end of the human scale

The deepest mine in the world works at about this depth. As far as we know, no person has gone further into rock. From here it is machines only.

4,500 m

The first surprise

Rock should get denser with depth. Here it gets looser: density and wave speed drop sharply.

"More than anything this amazes me: with depth we steadily observe a loosening of the rock," said E. V. Karus, who led the measurements.

4,700 m

The boundary that is not there

The forecast said the Proterozoic rock would give way to the granite layer here. It did not.

6,000 m

The spring

"At six kilometres the drill literally flopped into a spring of brine," the magazine Vokrug Sveta wrote in 1982. Into water that, in the magazine's words, last saw the sun two billion years ago.

6,500 m

Traces of life

Hundreds of forms of microscopic fossils were found in cores from down to seven kilometres: 24 species and 12 genera, B. V. Timofeev told a magazine in 1982. Other sources give other numbers.

The ode to the turbodrill by the expedition's senior geologist Yuri Smirnov has a line on it too: "found lumps of protein bodies in the water of the Proterozoic".

6,842 m

A jump of 800 million years

On this line the Proterozoic ends and the Archaean begins: above it the rock is about two billion years old, below about 2.8. The boundary is here, not at 4,700 metres. Between the layers lies an ancient surface that was once eroded away.

7,000 m

No basaltic layer

This was one of the main aims. At seven kilometres the seismic data promised the Conrad surface and the basaltic layer. Instead there is gneiss, and the basaltic layer does not turn up at any depth.

Soviet geologists put the jump in wave speed down to the same rock, loosened, with water released from it. Smirnov again: "rejected the mysterious Conrad, never found".

7,263 m

The flag

April 1975. The first rig, rated for 5,000 metres, stopped at 7,263 with more than 120 °C at the bottom. It was taken down, and until the new rig went up all that remained was the wellhead, marked by a flag. The hole sat idle for nearly a year and a half.

7,635 m

Iron

Iron quartzite. At 8,711 metres comes a layer where iron and titanium ore minerals make up 40–50% of the rock.

8,849 m

Everest

Everest, turned upside down, ends here.

9,052 m

Gold in the cores

A 2020 paper reports that gold nanoparticles were found in fluid inclusions in quartz from cores taken at 9,052 to 10,744 metres. The gold zone itself lies at 9,500–11,000 metres: the rock there holds 0.01 to 6.7 grams of gold per tonne.

9,101 m

Germany's KTB

Germany's superdeep KTB stopped at this depth in 1994. It was about 265 °C there. It is far cooler here.

9,584 m

Ciao, goodbye

6 June 1979. America's Bertha Rogers had stopped at 9,583 metres back in 1974, when it met liquid sulfur. The log entry by shift master Fyodor Atarshchikov: "Bottom, 9,584 metres. Bertha Rogers, ciao, goodbye!"

10,000 m

Ten kilometres

10 May 1980. 180 °C instead of the expected 100. Mud comes back to the surface at 45 °C. At these depths the bit is cutting rock for only 3.1% of the time.

"You thought we drill here? Mostly we go down and up," laughed the drilling foreman Valery Ivannikov.

10,910 m

China's Shenditake-1

February 2025. The world's second-deepest vertical well, according to Chinese state media: 10,910 metres. About 300 days went on the last 910 metres.

10,935 m

The Mariana Trench

From the ocean surface to the bottom of Challenger Deep is 10,935 metres. But the wellhead stands about 350 metres above sea level, so the hole only reaches that level about 350 metres further down.

12,000 m

Twelve kilometres

27 December 1983, 4 pm. Twelve kilometres. About 212 °C here instead of the expected 120: so says a 2021 review, without saying when it was measured.

In August 1984 more than 5,500 geologists from over 100 countries come to Moscow for a congress, and guests travel to the rig. On display is a worn, slightly rusty drill head. The president of the International Union of Geological Sciences hopes for 15 kilometres: "In the kingdom of hope there are never winters."

12,066 m

27 September 1984

The first run after the congress. They drill nine metres and start to lift. The string sticks, and then the load suddenly falls away. The turbodrill and five kilometres of pipe stay in the hole. They spend seven months trying to get them out.

They cannot. The drilling has to go on in a new bore, from 7,010 metres.

Go back.

7,010 m

Seven kilometres. Again.

You have been here before. This is a different bore, started off the first at 7,010 metres. Those five kilometres of pipe stayed in the old one.

8,500 m

The hole is no longer round

Below seven kilometres the rock is weaker and fractured. In cross-section the bores are mostly oval, up to 57 centimetres across the long side. Caverns reach 60–150 metres tall.

11,000 m

Four hours and eighteen

One run at 12 kilometres: 4 hours of drilling, 7–10 metres gained, then 18 hours taking the string down and up. In the last phase they made up to 60 metres a month.

12,000 m

Twelve kilometres, again

They got back to this depth only six years after the accident. Geologists would later call 12 kilometres, give or take 200 metres, critical for all the bores.

12,262 m

The bottom

1990. 12,262 metres. No cavern, no discovery. Rock about 2.8 billion years old, about 215 °C by calculation. That is about a third of the way through the crust here and 0.19% of the way to the centre of the Earth.

This bore too was abandoned after an accident. As far as we could find, nothing has reached this point since. Drilling for depth stopped in 1992, and the director named the end of funding as the reason.

12,262 m

Below the bottom

The hole has ended. The page has not. From here on, the depths exist only on paper.

12,875 m

Conan Doyle, 1928

In "When the World Screamed", Professor Challenger bores through a crust "roughly eight miles" thick and the Earth lets out a howl. Eight miles is about 12.9 kilometres.

13,000 m

13,000 metres

In 1992 they were still setting a casing string so as to drill on to 13 kilometres. It went no further.

13,400 m

13,400 metres

This much was promised for the Eleventh Five Year Plan, with another geophysical boundary expected here.

14,400 m

The Well to Hell

In the legend that spread in 1989 and 1990, geologists drilled 14.4 kilometres, measured 1,100 °C and heard human screams. The hole never came here.

In 1990 the radio host Rich Buhler followed the chain of retellings and found a Norwegian teacher who had added a forgery to the story: "I fabricated every word of it!" The project's director said: "We raised no devils and heard no sounds."

15,000 m

15,000 metres

The rig was built for this much. Everything ever planned ends here.

3,000 m

They really did listen

Remember three kilometres? From 2000 to 2003, instruments in this hole recorded noise in the 100–500 hertz band, down to about 6,800 metres. It rose at faults, where fluids move. And a thermometer at 3,000 metres showed, for months, swings with periods of 0.75 to 1.75 days, correlated with tides from the Moon and Sun.

Not screams. Rock and water answering the Moon and Sun, though not strictly in step.

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The lid

In 2007 the staff were dismissed after a final report, and in 2008 the rig began to be taken apart. "The hole itself will stay forever," said the director.

It has: under a lid that in 2016 carried the wrong number. What it says today we do not know: a guide in 2026 speaks of 12,262. As far as we could find, nobody is listening to it now.

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