The Kola Superdeep Borehole was the Soviet Union's attempt to explore the depths of the Earth's crust in the 1970s. It followed a decade of other nations, like the U.S. attempting similar projects to understand the very nature of the Earth better.

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They all hoped to find out what was going on at such great depths, and, most importantly, just find out if they could do it. Despite their impressive achievement, all that remains of the site today are ruins and a welded shut cover plate.

Let's take a look at how deep they managed to get and what they found down there.

What is the Kola Superdeep borehole?

The United States made the first attempts in the 1960s with the ambition of reaching the Earth's mantle. By doing this, they hoped to gain some valuable information on the Earth's age, makeup, internal processes, and help understand plate tectonics.

Whilst it might seem a bit of fool's errand to some, it potentially could have found some serious scientific treasure. As Benjamin Andrews explained in a Smithsonian article:

“If we have a better knowledge of what the mantle is and how the mantle behaves, we have better knowledge of volcanoes and earthquakes, and better knowledge of how the planet as a whole works,”



Other similar attempts were made in Guadalupe and Mexico under the something called Project Mohole. One historian would later describe this as "the Earth Sciences' answer to the space program."

The Soviets had a less ambitious target. They wanted to see if it was possible to drill down 15km or until they hit insurmountable technical difficulties.

Work began on the Kola Peninsula, NW Russia, in 1971. By 1979 the project had broken all other world records for drilling depth by beating that held by the Bertha Rogers Hole in Oklahoma, the U.S. at 9,583 meters.

But they kept going. By 1983 the drill had reached an unbelievable depth of 12km. Unsurprisingly, Soviet engineers were jubilant and apparently decided to take a year off.

During the hiatus, the scientists and politicians from around the world made visits to the site. But the site's equipment was left to basically rot during the hiatus.

Drilling commenced the following year but a 5km section of the drill string completely sheared off. After failed attempts to recover it was finally abandoned, the project started a new drilling project a 7km depth down the existing hole.

It took the team another 5 years, in 1989, to reach their previous 12km mark but drilling was later ceased due to some serious technical challenges. Temperatures at the drill head were in excess of 180 degrees Celsius which, at that time, were too technically challenging to overcome.

Whilst the team had expected to reach 13.5 km by 1990, and 15 km by 1993, they were forced to stop operations in 1992.

What was found in the Kola Superdeep borehole?

The primary reason for the Kola Superdeep Borehole was one of pure scientific intrigue. The team wanted to see if they could find anything interesting about the nature of the Earth's crust.

By the time the team hit serious technical challenges, the project was closed down and deemed a great success. Whilst they were not able to reach their target of 15km, they did uncover some interesting information.

The borehole facility is practically a ruin today. Source: Bigest/Wikimedia Commons

Prior to drilling, it was expected that there should be a granite-basalt boundary at around 7km depth. This was discovered to not be true.

In fact, what they found was a highly fractured area that was thoroughly saturated with water. This was highly unexpected, especially at such a depth.

They were also able to find evidence of microscopic planktonic fossil at depths around 6km. Another unexpected discovery was a large quantity of hydrogen gas.

The mud that flowed out of the hole was described as "boiling" with hydrogen.

How deep is the Kola Superdeep borehole?

After the second phase of drilling at the Kola Superdeep Borehole, the team managed to reach an impressive depth of 12,262 meters in 1989.

This crushed all previous records but wasn't to last.

In 2008, an oil well drilled at Al Shaheen Oil Field in Qatar was able to break the Kola Superdeep boreholes record. Drillers were able to reach 12,289 meters and are still, today, the deepest borehole in the world.

Another borehole, the Sakhalin-I Odoptu OP-11 Well (offshore from the Russian island of Sakhalin) also managed to beat both records in 2011. The drill team was able to reach an impressive 12,376 meters.

But, it should be noted, that for true vertical height, the Kola Superdeep Borehole still retains the title for the deepest borehole.