The deepest hole we have ever dug


During the Cold War, the US and Soviets both created ambitious projects to drill deeper than ever before.

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The lakes, forests, mists and snow of the Kola Peninsula deep in the Arctic Circle can make this corner of Russia seem like a scene from a fairy tale. Yet amidst the natural beauty stand the ruins of an abandoned Soviet scientific research station. In the middle of the crumbling building is a heavy, rusty metal cap embedded in the concrete floor, secured by a ring of thick and equally rusty metal bolts.

According to some, this is the entrance to hell.

This is the Kola Superdeep Borehole, the deepest manmade hole on Earth and deepest artificial point on Earth. The 40,230ft-deep (12.2km) construction is so deep that locals swear you can hear the screams of souls tortured in hell. It took the Soviets almost 20 years to drill this far, but the drill bit was still only about one-third of the way through the crust to the Earth’s mantle when the project came grinding to a halt in the chaos of post-Soviet Russia.

The Soviets’ superdeep borehole isn’t alone. During the Cold War, there was a race by the superpowers to drill as deep as possible into the Earth’s crust – and even to reach the mantle of the planet itself.

Now the Japanese want to have a go.

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“It was in the time of the Iron Curtain when the drilling was started,” says Uli Harms of the International Continental Scientific Drilling Program, who as a young scientist worked on the German rival to the Kola borehole. “And there was certainly competition between us. One of the main motivations was that the Russians were simply not really open with their data.

“When the Russians started to drill they claimed they had found free water – and that was simply not believed by most scientists. There used to be common understanding among Western scientists that the crust was so dense 5km down that water could not permeate through it.”

“The ultimate goal of the [new] project is to get actual living samples of the mantle as it exists right now,” says Sean Toczko, programme manager for the Japan Agency for Marine-Earth Science. “In places like Oman you can find mantle close to the surface, but that’s mantle as it was millions of years ago.

Wilderness in Kola peninsula (Credit: Getty Images)

“It’s the difference between having a live dinosaur and a fossilised dinosaur bone.”

If the Earth is like an onion, then the crust is like the thin skin of the planet. It is only 25 (40km) miles thick. Beyond this, is the 1,800-mile deep mantle and beyond that, right at the center of the Earth, is the core.

Like the space race, the race to the explore this unknown “deep frontier” was a demonstration of engineering prowess, cutting-edge technology and the “right stuff”. The scientists were going where no human had gone before. The rock samples these super-deep boreholes could supply were potentially as important for science as anything Nasa brought back from the moon. The only difference was that this time the Americans didn’t win the race. In fact, no-one really did.

 The Soviets started to drill in the Arctic Circle in 1970

The US had fired up the first drill in the race to explore the deep frontier. In the late 1950s, the wonderfully named American Miscellaneous Society came up with the first serious plan to drill down to the mantle. The society-turned-drinking-club was an informal group made up of the leading lights of the US scientific community. Their crack at drilling through the Earth’s crust to the mantle was called Project Mohole, named after the Mohorovičić discontinuity, which separates the crust from the mantle.

Rather than drill a very, very deep hole, the US expedition – observed by novelist John Steinbeck – decided to take a short cut through the Pacific Ocean floor off Guadalupe, Mexico.

The advantage of drilling through the ocean floor is that the Earth’s crust is thinner there; the disadvantage is that the thinnest areas of crust is usually where the ocean is at its deepest.

The Kola Superdeep Borehole (Credit: Rakot13/CC BY-SA 3.0)

The Soviets started to drill in the Arctic Circle in 1970. And finally, in 1990, the German Continental Deep Drilling Program (KTB) began in Bavaria – and eventually drilled down to 5.6 miles (9km).

As with the mission to the Moon, the problem was that the technologies needed for the success of these expeditions had to be invented from scratch.

When in 1961 Project Mohole began to drill into the seabed, deep-sea drilling for oil and gas was still far off. No one had yet invented now essential technologies such as dynamic positioning, which allows a drill ship to stay in its position over the well. Instead, the engineers had to improvise. They installed a system of propellers along the sides of their drill ship to keep it steady over the hole.

Two years before Neil Armstrong walked on the moon, US Congress cancelled the funding for Project Mohole when costs began to spiral out of control

One of the biggest challenges the German engineers faced was the need to drill a hole that is as vertical as possible. The solution they came up with is now a standard technology in the oil and gas fields of the world.

“What was clear for the experience of the Russians was that you have to drill as vertical as possible because otherwise you increase torque on the drills and kinks in the hole,” says Uli Harms. “The solution was to develop vertical drilling systems. These are now an industry standard, but they were originally developed for KTB – and they worked until 7.5kms (4.7 miles). Then for the last 1.5–2km (.9 to 1.25 miles) the hole was off the vertical line for almost 200m.

German borehole project (Credit: Jochem Kueck)

“We tried to utilise some of the Russian techniques in the early 90s or late 80s when Russia became more open and willing to cooperate with the West,” he adds. “Unfortunately, it was not possible to get the equipment in time.”

However, all of these expeditions ended in a degree of frustration. There were false start and blockages. Then there were the high temperatures their machinery encountered that deep underground, the cost and the politics – all of which put paid to the dreams of the scientists to drill deeper, and break the record for the deepest hole.

Two years before Neil Armstrong walked on the moon, US Congress cancelled the funding for Project Mohole when costs began to spiral out of control. The few metres of basalt that they were able to bring up worked out at a cost of roughly $40m (£31m) in today’s money.

When Dutch artist Lotte Geevan lowered her microphone protected by a thermal shield down the German borehole it picked up a deep rumbling sound that scientists couldn’t explain

Then it was the turn of the Kola Superdeep Borehole. Drilling was stopped in 1992, when the temperature reached 180C (356F). This was twice what was expected at that depth and drilling deeper was no longer possible. Following the collapse of the Soviet Union there was no money to fund such projects – and three years later the whole facility was closed down. Now the desolate site is a destination for adventurous tourists.

The German borehole has been spared the fate of the others. The huge drill rig is still there – and a tourist attraction today – but today the crane just lowers instruments for measurement. The site has become in effect an observatory of the planet – or even an art gallery.

When Dutch artist Lotte Geevan lowered her microphone protected by a thermal shield down the German borehole, it picked up a deep rumbling sound that scientists couldn’t explain, a rumbling that made her “feel very small; it was the first time in my life this big ball we live on came to life, and it sounds haunting,” she says. “Some people thought it did sound like hell. Others thought they could hear the planet breathe.”

“The plan was there to drill deeper than the Soviets,” says Harms, “but we hadn’t even reached our allowed phase of 10km (6.25 miles) in the time we had. Then where we were drilling was just much hotter than where the Russians were. It was pretty clear that it was going to be much more difficult for us to go any deeper.

“By then it was also the early 90s in Germany and there was no good argument to raise additional funding to go any deeper because the German unification was costing such a lot of money.”

It is hard not to shake off the feeling that the race to the Earth’s mantle is an updated version of the famous novel Journey to the Centre of the Earth. While the scientists don’t expect to find a hidden cavern full of dinosaurs, they do describe their projects as “expeditions”.

“We thought of it as an expedition because it really took some time in terms of preparation and execution,” says Harms, “and because you’re really going into no-man’s land, where no-one has been before, and that is really unusual today.

The thing about these missions is that they are like planetary exploration – Damon Teagle

“You always find down there something that really surprises you, and especially if you go down into an area that is very deep in the crust.

“And if we talk about KTB or the Kola Superdeep, then the theories that were behind the goals of the project were 30–40 years old by the time drilling started.”

“The thing about these missions is that they are like planetary exploration,” says Damon Teagle, professor of geochemistry in the School of Ocean and Earth Science, National Oceanography Centre Southampton at the University of Southampton, who has been heavily involved in the new Japanese-led project. “They are pure science undertakings and you never know quite know what you are going to find.

“At Hole 1256 [a hole drilled by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP)], we were the first get to see intact ocean crust. No one had got to it before. It was really exciting. There are always surprises.”

Derelict Kola Super Borehole (Credit: Rakot13/CC BY-SA 3.0)

Today, “M2M-MoHole to Mantle” is one of the most important projects of the International Ocean Discovery Program (IODP). As with the original Project Mohole, the scientists are planning to drill through the seabed where the crust is only about 6km (3.75 miles) deep. The goal of the $1bn (£775m) ultradeep drilling project is to recover the in-situ mantle rocks for the first time in the human history.

“To do this would be an amazing undertaking and require a huge commitment from Japan,” says Teagle, who is involved in the project.

Despite the importance of the project, the huge drilling ship the Chikyū was built almost 20 years ago with this project in mind. The Chikyū uses a GPS system and six adjustable computer-controlled jets that can alter the position of the huge ship by as little as 50cm (20in).

“The idea is that this ship would pick up the torch and continue the work started by the original Mohole project 50 years ago,” says Sean Toczko, programme manager for the Japan Agency for Marine-Earth Science. “Superdeep boreholes have made a lot of progress in telling us about the thick continental crust. What we are trying to do is find out more about the Crust-Mantle boundary.

These expeditions are extremely expensive – and therefore they are difficult to repeat – Uli Harms

“The main sticking point is that there are three main candidate sites. One of those is off Costa Rica, one off Baha, and one off Hawaii.”

Each of the sites involves a compromise between the depth of the ocean, distance from the drilling site and the need for a base on the shore that can support a billion-dollar, 24-hours-a-day operation at sea. “The infrastructure can be built up, but that takes time and money,” adds Toczko.

“In the end, it really is a cost issue,” says Harms. “These expeditions are extremely expensive – and therefore they are difficult to repeat. They can cost hundreds of millions of euros – and only a small percentage will actually be for the earth sciences, the rest will be for technological development, and of course, operations.

“We need inspiring politicians to talk up the value of these expeditions.”

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