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Kola Superdeep Borehole: The Deepest Hole Ever Made

The 20th Century saw the cold war battle for the stars, as the USSR and the USA raced each other into space, and eventually to the moon. But there was another short-lived race that took place between the two superpowers that never quite captured the imagination in the same way. A race that, instead of going up, went straight down. 

Almost entirely within the Arctic circle, the Kola Peninsula in northwestern Russia is a barren land of mountains and tundra. A harsh environment – beautiful yet bleak – and home to one of the most extraordinary engineering feats of all time. This was a scientific project which lasted twenty-two years and pushed the boundaries of both human achievement and our understanding of planet Earth. But today, all that remains is a small rusted metal plate, seemingly bolted straight into the ground. Beyond this metal cap lies a vast empty chasm – the deepest man-made hole in the world – the Kola Superdeep Borehole. 

Compared to space exploration you might find it harder to muster the same kind of enthusiasm about holes in the Earth, but what was dug at Kola remains an astonishing achievement. At just 9 inches in diameter, it is smaller than most standard pizzas, but at a depth of 12,262 meters (40,230 feet), it is unparalleled. This hole travels 7.5 miles underground, and yet still only equates to about 0.2% of the distance to the centre of the planet. 

Direct view of the kola super deep borehole. Currently welded shut.
Direct view of the hole. Currently welded shut.by Rakot13 is licensed under CC-BY-SA

What remains of the Kola Borehole area can be found 10km from the small town of Zapolyarny, just twenty kilometres from the Norwegian border. During the heyday of the Soviet Union, and after the discovery of oil and gas reserves in the area, the population of this traditionally sparsely populated area boomed, but the 1990s saw an economic crash, and numbers collapsed rapidly. Today, Zapolyarny is a grim town, with its claim to fame also a rusting heap nearby.           

But let’s get back to the hole itself. Why was it done? Well, almost entirely in the name of science. Soviet planners had hoped to be able to drill down to 15,000 meters in order to learn more about the Earth’s crust, and the mantle beneath it. Considering the mantle makes up about 75% of the planet’s structure, our knowledge about it is primitive, to say the least. We know more about the surface of the moon than what lies this far down on Earth. No doubt there was also a sense of prestige and competition involved, beating the Americans at anything during the cold war was always cause for celebration. 

The Center of the Earth

While the subterranean genre of fiction had existed before it, the release of Jules Verne’s Journey to the Center of the Earth in 1864, really sparked the interest of what lies beneath us. The tale involving a German professor and his nephew travelling through the Earth via volcanic tubes and discovering prehistoric animals along the way may be a thrilling piece of fantasy, but it certainly lodged deep in the imagination of many.  

Before we jump in – pun intended – let’s focus a little on the geology. The outer skin of the Earth is the crust, a section which varies in thickness depending on where you are but is generally between 3 and 43 miles thick. At the lower limits of this lies the Mohorovičić discontinuity, which is in effect the boundary between the crust and the mantle. The mantle is vast, believed to be around 1800 miles thick and made up of a combination of rocks, minerals and gases, including silicon, iron, magnesium, aluminium and oxygen. Finally, at the centre of the Earth lies the core. We believe it is composed mostly of an iron-nickel alloy with temperatures reaching somewhere in the region of 5430°C  (9806 °F) – which interestingly is around the same temperature as the surface of the sun. However, almost all of this is based around scientific theory, rather than known fact. The initial goal of the Kola Superdeep Borehole was to drill down into the Mohorovičić discontinuity and to retrieve samples that would allow us to see this part of the planet for the first time. 

Project Mohole 

While the space race captured the imaginations of millions around the world, the alternative race underground never quite had the same impact. And while it was the USSR that led the way into space, it was the Americans who pioneered the earliest attempt underground. The idea of drilling a hole deep enough to take samples of the Mohorovičić discontinuity had emerged in the United States in the late 1950s and stung by the success of the Soviet Sputnik satellite, the Americans pressed on. By 1961, a group of scientists known as The American Miscellaneous Society were ready. 

Project Mohole in the sea

While the borehole at Kola would later be drilled on land, Project Mohole would be undertaken at sea, for the simple reason that the Earth’s crust was thinner from the seabed than from the same point on land. Drilling began from an oil ship, CUSS 1, in March 1961 and quickly became a success with multiple test boreholes drilled, the longest of which was 183 m (601 ft). However the project quickly ran into management and funding issues, and in 1966 was scrapped completely, at a final cost of $57 million. The race was over before it had even started. Things started much slower in the Soviet Union but would outlive the American venture by decades. 

Drilling Begins

Four years later in 1970, work began on the Kola Superdeep borehole, but as you can imagine this was a slow laborious task. Those involved faced numerous challenges, not least because the technology needed had to be invented as they went along. A specific drill was designed where only the drill bit at the end of the shaft rotated, while a lubricant comprised mostly of pressurized drilling mud was pumped down to it through a different drill in order to keep it cool and allow it to spin at 80 revolutions a minute.    

While the drill at Kola was slowly making its way down, the record for the deepest man-made hole in the world was broken – by the Americans. In 1972 an oil-exploratory hole known as Bertha Rogers in Oklahoma reached a new record of 9,583 m (31,441 feet). But its reign was short-lived, and on 6th June 1979, the Kola Borehole surpassed it. 

Scientific Findings

One of the reasons that this project took so long was the drilling was halted sporadically over the years. It became a popular site for politicians to visit, no doubt eager to bask in the glory of delivering a bloody nose to the Americans, but most of the stoppages were for scientific reasons.    

Of course, drilling the hole was only part of the challenge. Soviet scientists were eager to test the rock that the drill was moving through, but this posed a very unique problem. With enormous temperature and pressure difference between the bottom of the hole and the surface, rocks would quite simply turn to dust by the time they had been removed. Scientific instruments needed to be created that could measure the integrity of rocks while safely inside the hole. This led to a number of startling discoveries.  

One of the earliest finds was, funnily enough, something they didn’t find. Geologists had long assumed that a transition from granite to basalt occurred somewhere between three and six kilometres down, an area of transition between the upper and lower crust known as the Conrad discontinuity. However, as the Kola borehole reached deeper and deeper, it never found this transition. 

This theory had been based on seismic-reflection surveys, but what was found in Kola led many to speculate that in fact these reflections were being caused by a metamorphic change in the rock, mainly from extreme heat and pressure, rather than any actual change in rock type.

It had also long been assumed that the Earths crust so far down couldn’t possibly contain water because it was so dense, but low and behold, significant amounts of hot mineralised water was in fact found.  

Perhaps the most significant find, however, was the biological activity discovered. Scientists found 24 different types of fossilized microscopic organisms in rocks thought to be over two billion years old. These pale in comparison with the oldest found on earth at 3.7 billion years, but considering the temperature and pressure they were found in, it was a remarkable discovery. Even to this day scientists have struggled to explain why such fossils would be 6,700 metres (22,000 feet) below the surface of the Earth. 

The Urban Myth 

Now, just for a moment, let’s step from science to the occult, because the Kola Borehole has long been associated with an urban myth that began circulating in the late 1980s. The much re-told story, which either emanated from Norway or the USA, tells of a group Russian scientists drilling down deep into the earth – sound familiar?  After passing 14 kilometres they punched through into a large empty cavity below. Curious about what was inside, they lowered a heatproof microphone down the hole and eventually into the cavity. The sounds coming through the crackling speaker were simply terrifying, as the scientists realised that the cavity below was hell itself, with the tormented screams of the damned drifting upwards. 

The fact that the story was based in Siberia, and not Kola, hasn’t stopped the obvious connections being made. Now, of course, we regard this as nothing more than an urban myth, but coincidentally shortly after the story emerged, drilling ceased as Kola, which only inflamed the rumours that drilling stopped in an attempt to contain the underworld.           

The End of the Road  

When drilling finally came to a stop in 1992 it was because of two significant factors – and let’s just assume that they didn’t, in fact, find hell down there. With the Soviet Union collapsing this kind of expensive project was no longer feasible. But a much more immediate problem had arisen at Kola. Temperatures had soared to 180 °C (356 °F) at the bottom of the hole, almost double what had been expected. Had there not been political upheaval in Russia at the time, it’s unlikely that the machinery being used would have been able to push down any further. Geologists at the time commented that the rock that far down behaved much more like plastic, or soup, than rock. 

But this wasn’t quite the end. Though no further drilling took place, the laboratory at Kola remained open for a number of years with the help of international funding, but in 2008 the site was finally abandoned, and the borehole was covered.    

Questions have been asked ever since as to whether we could go further. A German drilling project reached a depth of 9,101 metres by the time it ceased in 1995, while the Japanese drilling ship, Chikyū, which was launched in 2002 with a mandate to explore the mantle in the hope it may help to understand earthquakes, has been steadily increasing its drilling depth, but has also faced enormous problems. Huge strides have been made, especially with ocean drilling, but the mantle, and Kola’s record, still stands a long way off. The race, it seems, is still very much on.

Today, what was once a glorious venture, has come to a rather inglorious ending. The site of the Kola Superdeep Borehole lies in ruin with many of the buildings now collapsed. There are no signs, or plaques that tell of the historic achievement that occurred here. The floor is littered with jagged rusting metal. But if you look closely, you will find one small metal plate held firmly to the floor by twelve sturdy bolts. And beneath it? Well, it’s a long way down.     

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