Chevé Cave (pron Chay-vay), pictured above, is Mexico's best hope. It's L-shaped system has so far been navigated to a depth of 4,869ft (1,484 meters). American supercaver, Bill Stone, and his team then arrived at huge boulders, which they couldn't squeeze through. But water was passing beneath. They dropped dye into the subterranean river, then discovered where that emerged on the surface. They know that the cave is deeper still, they just need to work out how to explore it.
Chevé Cave begins with a 1,247ft (380 meters) sheer descent. The shaft then kinks to the west, sloping downwards for the remaining known 3622ft (1,104 meters). At this point, cavers encounter a terminal sump. That is a section that is completely flooded. Short sumps may be explored with cavers holding their breath, as they swim through it. But this one is too big. It will require cavers to lug proper diving equipment down there. An intimidating prospect considering the obstacles that have to be traversed before they even reach the waters.
Chevé's biggest rival is Krubera Cave, in Abkhazia, Republic of Georgia. A Ukrainian supercaver has finally charted its depths at 7,188ft (2,191 meters). Krubera Cave currently holds the title as the world's deepest pit. However, its extent is known. Chevé's is not. Yet finding out how deep it is requires amazing feats of human endurance.
Image froma 2004 expedition into Chevé
It is said that there are over 50 ways to die in a supercave. Falling is only the most obvious. Hypothermia, electrocution and sheer panic have all taken their victims. These cavers are underground for up to a month, as it takes a week to even get to the area where exploration can take place. During this time, they are usually in pitch darkness. They encounter pockets of poison gas, vast lakes and flooded chambers. Water levels can rise suddenly, if a flash storm occurs on the surface. There is no way to warn those below that this has happened.
Temperatures can plummet or soar, often quite quickly. One of the biggest dangers of Krubera is freezing to death. Sounds echo in the vast systems. Bill Stone described a 150ft (46 meters) waterfall, in Mexico's secondest deepest cave, Huaulta. He said that the noise was like standing next to a jetliner's engine, for days on end, without being able to get away. Moreover the mind can play tricks on you down there.
There is a phenomenom known as 'the Rapture'. It is not pleasant to experience. Supercave exploration taught us that every human being has a limit. It differs from person to person, but there is only so much darkness and depth that each of us can take. When that points is reached, a switch clicks in the brain and that individual is gripped by 'the Rapture'. It manifests as the biggest panic attack ever. They need to get out; and they need to get out NOW. No time for safety precautions. No consideration for the lives of your colleagues. It's fight and flight in overdrive. It's uncontrollable and they have to leave NOW!
This, naturally, is a bit of a problem, when you are a week's arduous journey from the surface and there's no way back without a lot of skill and self-control.
Sleeping takes place in camps, wherever the cavers can find a relatively broad ledge or underground beach to set one up. If they can't, then they tack a hammock between two boulders or onto the sheer face of a cliff. They dangle there to re-energize themselves with a little shut-eye. They carry with them food to sustain them. With any luck, they might even find a slab big up to rest their cooking gear onto it.
Sheer stamina and a high level of fitness has to keep them going. Some passages are so tight that only Yoga techniques can contort their lithe bodies enough to see them through. Often they are supporting their whole body weight with just a hand or strategically placed foot.
James M Tabor's book 'Blind Descent' tells the story of the supercavers, as they explore Chevé and Krubera.
Three miles on a level path–or even a mountain route–in daylight is one thing. Three miles immersed in absolute darkness, drenched by freezing waterfalls, wading neck-deep through frigid lakes, spidering up and down vertical pitches, scrambling over wobbling boulders, and belly-crawling through squeezes so tight you must exhale to escape them, is quite another…Imagine climbing the stairs of two Empire State Buildings in daylight, dry and unburdened. To get out, Vesely and Farr would have to do it in the dark, soaking, heavily loaded, on rope the diameter of a man’s index finger.
There is another, longer excerpt from this book on NPR's website. It compellingly describes a climb into Chevé Cave that ends in a fatality. There is also an interview with the author, which explains more about the conditions into which cavers descend, when exploring a supercave. That can be heard here.