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Hranice Abyss: The Deepest Flooded Freshwater Abyss in the World

The efforts to explore and map Hranice Abyss, located in Hranice (Přerov District) in the Czech Republic span more a century. Currently, the monstrous chasm is known to reach 384 m/1260 ft deep. Explorer and member of the Czech Speleological Society Michal Guba has the deets.

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By Michal Guba

The cave diving organization “7-02 Hranický kras,” which is a part of the Czech Speleological Society, is responsible for and has overseen the exploration of the Hranice Abyss, the deepest known flooded abyss in the world. The timeline below details the continuing exploration of the abyss. Please note that it is not easy to find divers who are technically and professionally prepared for exploration at a depth of about 200 meters/656 feet in a cave environment. 

In addition to depth, the composition of the water in Hranice Abyss can cause problems for divers. It is a mineral water (‘kyselka’ in Czech) with a high content of CO2 (carbon dioxide), which irritates the exposed parts of a diver’s body. In addition, the water’s composition has influenced the choice of diving equipment. When using open-circuit scuba, the exhalation bubbles cause a chemical reaction in the surrounding water, resulting in a rapid deterioration in visibility—it drops to zero! For that reason, open-circuit dives to depths below 50 m/164 ft were “banned” in 2001. Since then, members of 7-02 Hranice Karst have used closed-circuit rebreathers, which don’t emit bubbles, for exploration beyond 50 m/164 ft. Currently, the dive team has standardized on Divesoft’s Liberty rebreather.

1580: The first unsuccessful attempt to determine the depth of the lake at the mouth of Hranice was conducted by a breath-hold diver in 1580 and was described by Tomáš Jordán of Klauznburk. 

1900-1902: It was not until the turn of the 20th century that a professional teacher, J. V. Šindel of Hranice, repeatedly launched a weighted probe from a boat and reached a depth of 36 meters/118 feet. His findings were not challenged following exploration by geographer J. Dosedla in 1951, but they were quickly debunked by the arrival of divers and modern technologies.

1961: Bohumír Kopecký of Hranice made the very first dive in the Abyss with his handmade diving apparatus, reaching a depth of 6 meters/20 feet. 

1963: RNDr. Jiří Pogoda conducted a systematic dive survey. He found that the bottom forms a slope obliquely pointing deep under the rock massif.

1977: Miroslav Lukáš discovered the first dry space behind Zubatice. The location is called Heaven for its decoration. 

1978: Miroslav Lukáš and Jaromír Andrés discovered another dry space, named Dry Rotunda. There is a greater mouse-eared bat colony during the period from May to September.

1980:  A special glider probe by RNDr. Jiří Pogoda reached an unbelievable 260 m/853 ft.

This was followed by several dives with helium breathing mixture. 

1981: Fraňo Travěnec and Lubomír Benýšek descended for the first time with a trimix mixture to a depth of 110 meters/361 feet. After the borders opened in 1989, foreign divers also began to dive into the Abyss. 

1993: Belgian Michel Pauwels reached a depth of 155 meters/509 feet with a trimix mixture. Depth probes continue to measure areas too deep for cave divers to reach. 

1995: A remote-controlled underwater robot was first used in the Abyss. It was the ROV HYBALL, which at Lift I reached a maximum depth of 203 meters/666 feet; unfortunately, its supply cable got stuck in the fallen wood logs. The operator managed to maneuver it out but its Belgian owner, Carl von Basel, no longer wanted to continue the survey.

2000: Krzysztof Starnawski, who made the “last” deep dive with open-circuit scuba, reached a depth of 181 meters/594 feet and saw the bottom of the core of the Abyss, called Lift I. After the year 2000, divers began using closed-circuit rebreathers, which enabled them to stay longer at deeper depths. 

2003: The underwater robot ROV COLOMBO of the Main Mining Rescue Station a.s. (OKD Ostrava of the Czech Republic) was used to survey Lift I and the “New York” area. It reached a depth of 140 meters/459 feet but was limited by the length of its communication cable (150 meters/492 feet).

For a long time, it was certain that Krzysztof Starnawski of Poland and Pavel Říha saw the bottom at a depth of about 200 meters/656 feet, and that the possible continuation of the vertical direction did not lead directly to the current survey. Therefore, it was decided to provide an underwater robot rather than a diver to investigate the terrain and suggest further action. It was agreed to revive earlier collaboration with the Polish cave diver Krzysztof Starnawski.

2002-2010: Pavel Říha conducted an in-depth survey and mapped Lift I at a depth of 170 meters/558 feet.

2011:  Krzysztof Starnawski had just finished testing a unique, double closed-circuit instrument with which he dove in the Red Sea to the depth of 283 meters/928 feet. 

January 2012: Krzysztof Starnawski settled his 2000 record at 181 meters/594 feet at the Abyss. Two days later he descended to a depth of 197 meters/646 feet, creating a new depth record and discovering a narrow passage (restriction) on the north side that could perhaps be explored.

June 2012: Krzysztof Starnawski achieved an extraordinary discovery in another dive when with much difficulty, he overcame the restriction and descended to a depth of 223 meters/732 feet. By doing so, he confirmed that the Hranice Abyss continued to a greater depth than previous calculations. 

October 1, 2012: On his next dive, Starnawski descended to a depth of 223 meters/732 feet and launched a new probe, which reached 384 meters/1260 feet, setting a new Hranice depth record.

Since 2014: Members of ČSS ZO-7-02 Hranický kras have been using the Divesoft technology for exploration and research into the abyss. Specifically, the Liberty rebreather (back- and sidemount versions) enables members of ZO-7-02 Hranický kras to perform complex work activities up to 100 meters/328 feet (drilling, enlarging holes, positioning sensors, etc.), which fully utilizes the properties of the rebreather, such as low work of breathing and maintaining an optimal PO2. Members conducting dive surveys were also equipped with Freedom dive computers to ensure their safety in the complex depths and so-called “yo-yo profiles” in the Hranice Abyss, and providing for compatibility among the dive team.

June 2015: David Čani made a dive to a depth of 181 meters/594 feet (a new Czech depth record), in which he checked the status of the Lift I axis and, along with other dive participants, practiced procedures to ensure the safety of deep divers performing dives down to 200 meters/656 feet and below. 

July 2015: Krzysztof Starnawski made a dive to a depth of 220 meters/722 feet, and then launched a probe with an electronic pressure sensor. This time he measured the depth of just 365 meters/1198 feet. However, at the ascent, he made a very promising discovery when he examined a new restriction at a depth of 204 meters/669 feet and found that it opened into a passage big enough to drive a Tatra (a truck) through. This discovery was of paramount importance for the safety of divers making dives across the strait at the bottom of a massive well that was previously named as Lift I, because it might give them an alternate exit path.

August 21, 2015: Krzysztof Starnawski made a dive into another well (called Lift II), which was accessible after crossing the strait at a depth of 204 meters/669 feet and has approximately the same slope as Lift I. In this dive, Krzysztof discovered a new opening at 240 meters/787 feet (rock window) into unknown spaces, which he named “Macejko.” In doing so, Starnawski reached a maximum depth of 265 meters/869 feet, setting a new world depth cave record.

2016: The members of the Hranice Karst joined with National Geographic for the “Hranická Propast Step Beyond 400 meters” project with the help of Bartolomiej Grynda, owner of Gralmarine, to test an underwater ROV. On September 27, a new depth of 404 meters/1325 feet was reached during the Gralmarine ROV test dive, making the Hranice Abyss the deepest flooded cave in the world. The robot was again limited by the length of the communication cable of 500 meters/1640 feet. 

The ROV descended to the bottom of Lift I to the “Mikado” restriction and entered the Lift II. In Lift II, Grynda maneuvered the ROV along the cord of the measuring probe to a depth of 384 meters/1260 feet. After reaching the end, he proceeded along the wall to a depth of 404 meters/1325 feet. The robot remained “tangled” near the “Mikado” restriction in Lift I at close to 200 meters/656 feet. The robot was eventually rescued in 2017 by 7-02 Hranický kras and members of the Department of Special Diving Activities and Training from the Police Presidium of the Czech Republic.

2018: Working with the town of Hranice, the ČSS ZO 7-02 Hranický kras opened an information center at the Teplice nad Bečvou railway station detailing the current state of the Abyss exploration. There are 3D glasses available to help the tourists dive into the waters of the Abyss.

“During the dives, we discovered new irregular spaces, which will require further exploration. They are mostly deep and relatively narrow. However, none of the Hranice Karst speleologists doubt that there are still interesting discoveries to be made at Hranice Abyss,” explained 7-02 Hranický kras chairman Michel Guba.

At the moment, speleologists are working to produce maps of both the dry and flooded parts of the Abyss from top to bottom in 3 meter/10 foot increments. At the same time, photographic and video documentation is being conducted to help refine individual measurements.

To create greater awareness of the entire flooded and dry underground labyrinth to the public, all the measurements have been input into mapping programs to create a 3D model. Currently a profile of the cave is displayed on an information board showing the known spaces of the Abyss.

Currently there is an information board with a profile showing the current state of the known spaces on the observation ring near the Abyss.

Hranice Abyss Facts:

  • The deepest abyss of the Czech Republic.
  • The deepest flooded freshwater abyss of the world.
  • First written reference: 1580
  • Recorded on map: 1627
  • Cadastral area: Hranice.
  • Edge elevation of Abyss: 315 meters/1033.46 feet above sea level.
  • Entrance dry esophagus of the Abyss: length 104 meters/341 feet, width 34 meters/111 feet, depth 69.5 meters/228 feet.
  • The depth of the flooded part: 404 meters/1325.46 feet (2016).
  • The total depth of the Abyss: 473.5 meters/1553.47 feet.
  • Depth reached by divers: 265 meters/869 feet (2015).

Additional Resources:

Video of cave diver Jakub Šimánek diving in Hranice Abyss in 2017 recorded by Petr Chmel, a member of a diving club Pragoaquanaut.


Michal Guba worked as a policeman from 1992 to 2017. From 2008 to 2017, he worked as a lecturer, instructor, and deep diver. During a rescue mission (there was a huge flood in the Czech Republic in 1997), Michal decided to take a diving course at CMAS and began diving in 1998. Since 2000, he has been a part of the Hranice Abyss speleo diving team and is currently the chairman.

Michal participated as an expert (de-mine-pyrotechnic and training) on foreign missions in Switzerland, Austria, Bosnia and Herzegovina, Serbia, Croatia, and Montenegro from 2011 to 2016. Michal was awarded the Golden Rescue Cross in 2007 by the President of the Czech Republic Klaus and has received additional awards for his police work. Michael is currently employed by Czech company TRESPRESIDENTES s.r.o.

Cave

A Perspective on Teaching Cave CCR

Veteran Irish cave and CCR instructor cum sports psychologist Matt Jevon explains how he teaches divers to become competent underground rebreather divers who “err safely” and thus are likely to return home at the end of the dive.

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by Matt Jevon
Header image courtesy of Marissa Eckert

“To err is human” Alexander Pope

In his “Essay on Criticism,” Alexander Pope wrote “To err is human, to forgive divine.” However, if you are not prepared to err safely in cave or rebreather diving, you will come face to face with your preferred divine being, begging for forgiveness.

Stratis Kas’s book, Close Calls, a compilation of stories from a roll call of “who’s who” in diving, attests to the fact that the very best of us can and do make mistakes, or err. That they are still here to share these lessons with us affirms the huge amount of training, preparation, and experience required—and, as many will admit, no small amount of luck.

Gareth Lock, author of Under Pressure, is fond of the phrase “fail safely,” and with good cause. As he puts it, and I paraphrase; the human in the machine is at the heart of likely outcomes. In my own experience as a psychologist with expertise in human performance, the best systems, processes, and technologies are often outwitted by an unwitting fool or an arrogant wise man.

The ultimate dream of becoming a cave diver accessible for all? Photo by Marissa Eckert.

Today there is a surge of divers wishing to become cave divers, perhaps because it is perceived by some as the pinnacle of diving—in skill and status—or perhaps because it is seen as more accessible. Certainly, social media has given access to the incredible and beautiful environments that were once the playground of a select few. Divers are discovering that cave and modern diving practices, equipment, and training are making it a much safer environment until they start exploring virgin caves. Closed circuit rebreathers (CCR) are now mainstream and in wide use by many divers. In cave and deep dives, I would say they have become the primary tool; the limitations of open circuit scuba are seen as making it inappropriate for most “big” dives.

By the time a diver reaches their CCR cave course, they will, or should be, a knowledgeable, skillful, and competent diver on a CCR. Perhaps the odd one will find a shortcut, but it is the exception rather than the rule. In addition, the majority will already have some open circuit cave training, at least to intro level if not to full cave. The pathway from zero to hero in the cave is much longer and more difficult to shortcut than, say, open water to instructor status. Starting cave diving on CCR from cavern to full cave is, and should be, a much longer route.

[Ed.note: There are arguments against allowing a student to pursue any form of diving before gaining open circuit experience. Some argue that one should first become competent on open circuit in the relevant environment and THEN train in that environment on RB/CCR. This argument asserts that RB failures will find a diver on open circuit, requiring them to be proficient on this equipment in the relevant environment. These factors may be progressively more relevant with more complex environments.]

So, the CCR cave instructor is not dealing with an inexperienced CCR diver; nor, if they are as careful in their acceptance of students as most are, will they be dealing with an adrenaline seeking-junkie. See “Why We Cave Dive” (video) for reasons why some divers seek out the karst realm, as well as examples of divers we hope to encourage into the sport and those we prefer to avoid it.

How do we handle tricky situations? Photo by Mirsoslav Dvoracek

The job of a cave CCR instructor is not to prevent all errors or mistakes. It would be both arrogant and foolish to believe that instructors can overcome human nature and the situational factors found in closed circuit cave diving. The instructor’s role is to lessen the frequency and severity and to mitigate the consequences of those errors as, and when, they occur. The instructor must do this in the course, ideally exposing students to likely errors or challenges in controlled conditions and embedding appropriate solutions. Students should acquire appropriate and controlled emotional, cognitive, and behavioural responses.

Being a cave instructor has a few significant differences from being a deep technical rebreather instructor. Here are a few:

Kit

Cave diving demands a greater equipment load. The number of backups can be summarised as “Three is two, and one is none.” So, three sources of light sufficient to complete an exit, three cutting devices, reel/spools, markers, breathing sources, and more. Before entering any overhead environment, the instructor must help students configure, become familiar with, and master accessing and manipulating their configuration. For this reason, cave divers opt for simple, easy solutions that are robust and definitely not prone to failure. This applies to their primary gear (CCR choice) and to every single piece of backup gear.

Preparing the kit. Photo by Petr Chmel.

My own choices are primarily sidemount-based in the cave; the Liberty rebreather; Divesoft computers, primary reel and markers; plus O’Three 90ninety shell suit; and Apeks regulators and spools, all based on a Razor Sidemount System. In backmount I use a JJ-CCR, but I am now using the Liberty Sidemount rebreather as a bailout system. All simple, proven, tough, and each piece having substantial built-in redundancy/failure management options.

Safety

The instructor’s primary role—despite what many believe to the contrary—is, in any diving, to ensure that the students are safe and that they go home unharmed medically, physically, or mentally. Secondary to this is teaching skills, having fun, and awesome and epic dives. What a big ask in cave diving!

Progression in open water diving is more straightforward, especially using mixed gas. In the absence of narcosis, divers can build up deco time gradually and have a pre-rehearsed familiar exit/ascent permanently above them. Although not different in terms of time to exit, an open water deco ceiling somehow seems, to most, to be less of a psychological threat than several hundred tons of rock.

Penetration stress can occur within only a few meters. Photo by Kathrine Livins.

I have seen cave divers suddenly go from a point of being perfectly happy to being very unsettled and distressed within a few meters. There is actually a term for this: penetration stress. Penetration should be slowly built up over time with confidence in the linear distance built through many dives—some, but not all, including stressful exits (blind, bailed out, manual control, or touch contact). 

To do this, an instructor needs considerable empathy. Some instructors may shy away from this and instead use a pseudo militaristic approach by battering, bullying, or belittling the student, constantly tearing off masks, shutting down gas, or more. (We are talking personality types here, not problem solving training.) Stay away from these people at all costs.

Instructors cope with a high task load. Not only do they have to monitor the group’s penetration distance, navigation, and teamwork, but they also need to monitor the students and their own PO2, decompression obligations and time to surface (TTL), bailout supply and limits, on board gas supply, scrubber durations, as well as to teach. In order to do this, a few tricks are employed. Some of these may be useful when diving in any CCR team:

  1. PO2 monitoring. HUDS can easily be seen reflected in students’ masks. It’s much easier than trying to read someone’s handset.
  2. Instructor Ghost Mode. Not just used for sneaky (pre-warned and planned) drills, the lights off/blackout ghost mode is often accompanied by pull and glide along ceilings or cave walls where no damage to the environment is possible. Instructors, especially on quiet CCRs, can get within a few centimeters of a student without their knowing, or they can shoot ahead. It is a bad practice to turn off (as opposed to cover) one’s primarily in a cave. The on-off button/switch is a weak point, especially at depth—sufficient working backups are required.
  1. Buddy lights on CCRs are brilliant for instructor/team monitoring, Divesoft’s show up well and Sentinels almost too well. When I was a student, my instructor found ghost mode difficult to fully pull off, since I saw this green light above me every time he tried it!
Lights are an integral part of safely experiencing a cave. Photo by Kathrine Livine.

Teamwork

As an instructor, you want the students to develop their own robust team dynamic. If you are part of this, too often, students will always defer to your authority and default to you for leadership and solutions. So, if you do join the team to make up numbers, always be number 2, the weakest member, and play the part. Students don’t need to see how clever or skilled you are, they need to develop their own skills.

Navigation: Know the cave you are teaching in. For students’ first dives where I may not know them or their capabilities, I like to be in caves where a lost line would not be an issue for me in terms of exiting. Take Ressell in France for instance: A quick glance at the ceiling and a look at the scallop shapes in the rock, and I know which way is out.

Know where you are and where you’re going. Photo by Miroslav Dvoracek.

Pre-Dive Checks

These assume a whole other level of importance in cave and rebreather diving. A checklist is useful but only if you properly check everything on it. Turn backup lights on and off, breathe bailout regs at least 4-5 breaths. Fill and dump wings and drysuits. Prevention will ensure survival. It will also give students confidence, which means you are less likely to have issues, you’ll get a better response if you do, and you can actually enjoy the dive. [Ed.—Check out GUE’s Pre-Dive Sequence here]

Here are a few tricks I also like to instill:

  1. Link routines. For example, PO2 check and back reference. I use a hand mirror, so looking back is easy, and a quick over the shoulder is not difficult. Every time I check PO2, I look behind me. Caves often look very different on the way out and if I can, I will mentally imprint landmarks that I will see on exit. Some caves have distance markers every 100-150 m/328-492 ft on the main line, especially training caves. I’m not a huge fan of these for my own diving, as it’s a bit like graffiti; but, for trainees, PO2 plus back reference anytime you pass any navigational marker is a good routine.
  2. Wetnotes use. A good habit in a new cave is to make a note of time, distance, gas, and the navigation marking/direction in your wetnotes at any substantive navigation. On some dives, this will be two or three notes. Do this in some Mexican caves and you will get about 300 m/0.2 miles from the entrance and need a new Wetnotes book, so be sensible!


Finally, students will learn a lot of new skills, from what to do when you lose teammates, lose or become entangled in the line, encounter a broken line, have light and equipment failures, and more. Many of these will be done with blindfolds or blacked-out masks (mine say, “Use the force” on the front). On an open circuit, these situations can be challenging. On CCR, doing blackout drills while controlling loop content and volume, handling multi bailouts, and more, requires time both to learn and to embed. Don’t do it until you get it right, do it until you can’t get it wrong. Sometimes the lost line drill will provide unique challenges to get it right. If conducted correctly, you will probably get it wrong half the time!

Ultimately, graduating a new CCR cave diver is a moment to enjoy for the instructor—one with a need for appropriate gravitas and consideration. I have certified divers who were less proficient than other divers that I failed or asked to repeat. That was because a student’s attitude, mental strength, and sound decision-making ensured that they would likely go home safely from each dive. As the sign posted at the entrance of almost every cave reads, “Nothing in this cave is worth dying for.” There is an awful lot of cave diving worth living for, and I have been privileged to see some spectacular caves.

References:

 Barnson S.C. (2014) The Authentic Coaching Model: A Grounded Theory of Coaching. Human kinetics, Champaign, Il.

Troy A. Moles, Alex D. Auerbach & Trent A. Petrie (2017) Grit Happens: Moderating Effects on Motivational Feedback and Sport Performance, Journal of Applied Sport Psychology, 29:4, 418-433, DOI: 10.1080/10413200.2017.1306729

Swann, C., Crust, L., Jackman, P., Vella, S. A., Allen, M. S. & Keegan, R. (2017). Performing under pressure: Exploring the psychological state underlying clutch performance in sport. Journal of Sports Sciences, 35 (23),2272-2280.

Additional Resources:

The Darkness Beckons by Martyn Farr

Basic Cave Diving a Blueprint for Survival by Sheck Exley (Freedownload)

Facebook Pages/Groups:

Psychological Skills for Diving @PSTforDIVING

Diving Educators – Teaching and Learning Techniques (Group)

Human Factors in Diving

Web pages:

www.mattjevon.com

www.swt.ie

www.thehumandiver.com


Matt Jevon, M.Sc. F.IoD, is a Full Expedition level Trimix and Cave instructor on OC and CCR with TDI and ANDI. He is a JJ-CCR and Divesoft Liberty Sidemount instructor and dealer for Ireland. Matt’s personal diving has included cave exploration in the Philippines and wreck projects in Croatia and Ireland, and he was one of the inaugural Dirty Dozen in Truk! Matt has held accreditations as an interdisciplinary sports scientist, sports psychologist with the British Association of Sport and Exercise Sciences (BASES), and was a British Olympic Registered Strength and Conditioning Coach and invitee on the Olympic Psychology Advisory Group. Matt works in the high performance business as a board advisor and non-exec, high performance sport, and expeditionary level diving as a partner in South West Technical Diving in Ireland (), and hosts the Facebook page “Psychological Skills for Diving.”

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