Over 40 years ago, scientists began this ambitious drilling project to penetrate the Earth’s crust and sample the area where the crust and mantle intermingle, the so-called Mohorovičić discontinuity.
After eight years of preparations and constructions, drilling began on 24 May 1970. In 1979, the world depth record held by the Bertha Rogers hole in Oklahoma, United States at 9,583m was broken. In 1983, the drilling hole had reached a depth of 12,000m and drilling was paused to carry out numerous scientific investigations.
When drilling resumed, the drill went 66 further meters until a 5,000m section of the drill string twisted off and was left in the hole. Drilling was later restarted from 7,000m in a new drilling hole called SG-3. In 1989, 19 years after researchers had broken ground, the project reached a depth of 12,262m and the Kola Superdeep Borehole became the deepest hole ever created by humankind.
Because of higher-than-expected temperatures at this depth and location, 180°C instead of 100°C, drilling deeper was deemed unfeasible and the drilling was stopped in 1992, about 2.7km short of the 15,000m goal.
Before the hole was drilled, scientists could only hypothesize about the composition of the Earth’s crust. One of the most surprising findings to emerge from the well is that no transition from granite to basalt was found at the depth between three and six kilometers below the surface. Other unexpected findings were the discovery of a large quantity of hydrogen gas and 24 species of microscopic fossils.
Due to a lack of funding, the project was closed down in 2005. All equipment was scraped and the site has been abandoned since 2008. The borehole itself remains, with a metal cap drilled and welded to seal off the hole.
For two decades, the Kola Superdeep Borehole was also the world’s largest borehole, in terms of measured depth along the well bore, until surpassed in 2008 by the 12,289m long Al Shaheen oil well in Qatar, and in 2011 by the 12,345m long Sakhalin-I OP-11 well offshore the Russian island Sakhalin.
Similar drilling projects have been commenced by the United States and Germany, but neither was able to reach comparable depths.