The world of caving is sort of a story of two — two caves and two men. The two caves are Chevé in the state of Oaxaca, Mexico, and Krubera in the Arabika Massif of the Western Caucasus in Abkhazia, Georgia.
The two men are American Bill Stone, who has been exploring Chevé for well over a dozen years, and Ukrainian Alexander Klimchouk, who has been exploring Krubera since the 1980s.
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Since the beginning of the millennium, it has been a race to the bottom of the Earth, and the story of both men was told in James Tabor's 2010 book Blind Descent: The Quest to Discover the Deepest Place on Earth.
Until March 2018, Krubera, named for the Russian geographer Alexander Kruber, won the depth race. "The difference in elevation of the cave's entrance and its deepest explored point is 2,197 ± 20 meters (7,208 ± 66 ft)," notes Geologypage.
The entrances to the two caves couldn't be more different. While Chevé's is hundreds of feet wide, the entrance to Krubera is little more than a hole in the ground.
The world's depth record
First in 2007, and then in 2012, Ukrainian diver Gennadiy Samokhin set a world depth record by diving in Krubera's terminal sump. A sump is a passage in a cave that is submerged underwater. Samokhin set successive world records of 2,191 meters and 2,197 meters, respectively.
To create a cave as deep as Krubera, which is known as "The Everest of Caves," there must be karst terrain with an underlay of limestone into which water can seep to carve the cave. Karst is formed by the dissolving of soluble rocks such as limestone, dolomite, and gypsum.
The limestone in Krubera dates from the Cretaceous and Jurassic periods.
The only limiting factor to how deep a cave can be is how far groundwater can flow before the pressure becomes too great. Krubera contains many freezing sumps and waterfalls.
To test the depth and layout of caves, explorers dump non-toxic dye into cave streams then wait to see where it emerges. In the case of Chevé, dye placed in the stream at its entrance turned up in the Santo Domingo River eighty-five hundred feet below and eleven miles away, and it took eight days to get there.
If you think that men like Stone and Klimchouk must be dashing explorers, they are, but they're also sober scientists. Both have Ph.D.s - Klimchouk's in hydrogeology, and he works at the Institute of Geological Sciences, National Academy of Sciences of Ukraine. Stone's Ph.D. is in structural engineering, and he is the President and CEO of Stone Aerospace in Texas.
This past Fall, Stone said, "When you get into these massive systems you run into obstacle after obstacle, and this is why it becomes, in the truest sense of the old British South Pole expeditions, 'man against nature.' It's gloves off. Whatever technology you can throw at it is what we do, and we frequently are inventing our own gear, because it doesn’t exist."
Inventing his own gear is something Stone knows a thing or two about. In December 1987, Stone demonstrated the MK1 model rebreather at Wakulla Springs, Florida in a scuba dive that lasted 24 hours and used only half of the system's capacity.
Rather than normal scuba tanks, a rebreather absorbs the carbon dioxide of exhaled breath, which allows for the recycling of air. Oxygen is added to replenish what is used. No gas is discharged into the environment, and breathing endurance is enormously extended.
A new world depth record
In March 2018, Krubera lost its title of the deepest cave in the world to its neighbor Veryovkina Cave when Russian spelunkers led by Pavel Demidov and Ilya Turbanov reached its maximum depth of 2,212 meters (7,257 ft). Veryovkina and Krubera are the only known caves on Earth that are deeper than 2,000 meters.
Regardless of who eventually wins "Cave Wars," science is the big winner. Caves are filled with microbes that may lead to new medicines or antibiotics. Caves also hold evidence of the past climate and environment of our planet. NASA is interested in the caves because there may also be caves on Mars.