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Geo-Joint: Proving the Depths of Hranicka Propast

Posted on December 18 2018

Snorkelers can see a lot of great stuff, because the water over coral reefs often isn’t that deep. But to really get down into what the undersea has to offer, it’s going to take some scuba gear and the know-how to utilize it properly and safely. If you’re just in it for recreation, 130 feet is about the limit. Technical professional diving goes down to 200 feet and then much deeper with special mixed gases and diving bells. A few years ago, a specially trained diver went down to 1,090 feet, thereby setting a new world record. The dive down took only 12 minutes, but the resurfacing took 15 hours in order to avoid the bends. All this is pretty impressive, given the inherent dangers, the water pressure, the dark and cold, and just the freak-out factor of being so far from the big body of air we all spend our days in, and that is so essential to our survival. Still, it’s just a lot of water—a straight shot back to the surface. For some, this is just too easy.

There is water all over this planet, and there are divers who simply can’t resist exploring its reaches, wherever it goes. From open water, some explore caverns with wide mouths that allow a bit of light in, and feature some incredible scenery and life forms. For the really bold and curious though, there is cave diving. That includes both caves that extend deeper behind caverns, and those that are accessed from inland openings, usually in fresh water. Whether those who dive in such places are extremely motivated divers, or are cave explorers who refuse to let a little submersion get in the way of exploring underground, is a good question. Cave diving is known as a very dangerous activity, and is only done safely after extensive training and experience. Even exploring dry caves can be dicey enough, given the potential slips and falls into voids, and the possibility of getting lost or stuck. So cave diving is definitely not something for the casual diver. Recently, the world was witness to the amazing skills of a team of expert cave divers who rescued a soccer team of young boys in Thailand who had gotten marooned deep in a cave when the river in it rose with storm water. The scariest part of that was probably having to give those youths a crash course in scuba in order to undertake the most hazardous kind of diving on their very first attempt. The boys all made it out alive, but the danger was never far away—one of the professional divers lost his life while transporting air tanks for the rescue operation.

The Hranicka Propast, also known as the Hranice Abyss, is in the Czech Republic, also known as Czechia.

Informational sign at the Hurka u Hranic nature preserve illustrates the world’s deepest known cave system.

It’s pretty clear then, that cave diving is challenging at any level. Not long ago, divers explored a water-filled cave that goes deeper than any other, and far deeper than a diver can go. Over several years, Krzysztof Starnawski, a Polish cave diver of some repute, probed the Hranicka Propast cave in the Czech Republic to try and find its depth. Initially, Starnawski dove to 656 feet and found the way had become too narrow to follow deeper. He dropped a measuring line down this “squeeze passage” that showed almost world-record depth. Returning months later he found that the rocks in the pinched area had collapsed, and he was able to dive to 869 feet and lower a line to 1,214 feet. Clearly, the cave showed potential to go deeper. In September 2016, Starnawski laid out lines that helped guide an ROV (remotely operated vehicle) that can go much deeper than humans can, and relay the view through fiber-optic cable. The ROV was able to reach the 1,325 foot mark, where it ran out of cable. That depth bested the deepest known underwater cave, Pozzo del Merro, in Italy, by 39 feet, and the images showed Hranicka Propast continues on down.

Peering down into the abyss, the water-filled cave entrance is surrounded by steep, rocky walls.

Cavern diving affords some natural light.

Actual cave diving is a lot darker, confined, and hazardous.

The cave, or abyss, is carved into limestone, a common occurrence since rainwater and underground streams will dissolve that type of rock over time, but this one is different. Hot water rising up from the depths, rich in carbon dioxide, has eaten its way up into the limestone from below, which means the cave could go a great deal deeper. Diving in this carbonated water will make your skin itch, and has some corrosive effects on the mechanical probes, but those robots don’t complain about it, nor do they have to go through the long decompression process in 59 degree water. With their hardiness and a longer tether, the ROVs will no doubt soon extend the known depth of Hranicka Propast to an even greater world record.

Whether you call it the Czech Republic or Czechia, there’s a lot to see and do there besides cave diving, and this National Geographic travel map, available from, can help guide you around.





caption: Peering down into the abyss, the water-filled cave entrance is surrounded by steep, rocky walls.
source: Wikimedia Commons: Fext (CC by SA 3.0 Unported)

caption: Informational sign at the Hurka u Hranic nature preserve illustrates the world’s deepest known cave system.
source: Wikimedia Commons: Radim Holis (CC by SA 3.0)

caption: Cavern diving affords some natural light.
source: pxhere: Unknown (CC0)

caption: Actual cave diving is a lot darker, confined, and hazardous.
source: Wikimedia Commons: Ryan Cantey (CC by SA 3.0)

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