Kola Superdeep Borehole

It’s hard to imagine that under this small metal cap lies the world’s deepest borehole. Now surrounded by ruins, the Kola Superdeep Borehole was a scientific project undertaken by the Soviet Union in the 1970s to better understand the Earth’s crust. The crust is the earth’s outermost layer. It is a thin shell in comparison to the earth’s dimension—about 30 to 50 kilometers thick and is made of light rocks such as granite and basalt. The crust floats above the Earth’s mantle, the semi-solid mass of molten rocks that make up the bulk of the planet. Underneath the mantle is believed to lie a solid core of iron. The first attempt to drill through the crust was undertaken by the United States in the early 1960s. It was an ambitious attempt because the objective was not to simply drill into the crust but to drill all the way through it and into the mantle. In the process, geologists hoped to gain valuable insight into the earth's age, makeup, and internal processes, as well as to provide answers to the mystery of continental drift, which at the time was still controversial. In the spring of 1961, five holes were drilled off the coast of Guadalupe Island, Mexico, under Project Mohole, which was described by one historian as “the earth sciences' answer to the space program.” It was chosen to drill through the sea floor because the earth’s crust was thinner under the oceans. The hole reached only 183 meters before the government pulled funding and the project was abandoned in 1966. Five years later, the Soviets decided to take a crack at the crust. Unlike the Americans, the Soviets set a modest target depth of 15 km, but more realistically, they just wanted to see how deep they could go before technical difficulties became insurmountable. The drilling of Kola Superdeep Borehole. Image taken in 1974.