ZACATON: The Tragic Death of Sheck Exley

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Bret GilliamZacaton is the deepest of five ceynotes located on a large ranch, El Rancho Asufrosa, in northeastern Mexico. It was “discovered” by Jim Bowden and Ann Kristovich on a reconnaissance trip made at the end of two weeks of exploration and surveying in the Nacimiento Santa Clara, a cave system at the base of the El Abra near the Nacimiento Mante. Five ceynotes of variable size and character were located.

The team began the systematic exploration of the ceynotes. On May 2, 1990, divers Jim Bowden and Gary Walten entered the Nacimiento at the western boundary of the ranch. The river is formed by the spring run emanating from Zacaton. A typical “boil” was noted on the water’s surface near a limestone outcropping. Pursuing this current, the divers located a small cave and followed a northeast azimuth until they had exhausted the line on their reel. With passage obviously continuing, they turned the dive, obtained an additional exploratory reel, returned to their tie-off and resumed laying line. Now in the lead, Gary soon noticed a bottle green glow ahead. He covered his light and confirmed a natural light source that could mean but one thing, they had made a connection to the surface. The exuberant divers emerged into Zacaton at a depth of 26′ and surfaced in the beautiful ceynote which takes its name from the islands of tall grass, zacate, which float across it’s surface.

The “Proyecto” resumed the exploration of the five ranch ceynotes in April, 1993, fully equipped with mixed gas capabilities to allow the safer exploration of the deeper systems. Sheck Exley, perhaps the most renowned cave explorer of the era, joined the team for a week and with Bowden dove the previously unexplored depths. Zacaton revealed the greatest surprise. On air dives to 258 ft. by Bowden and 407 ft. by Exley, no bottom was in sight. The previously plumbed depth of 250 ft. was proven to be an error! The divers dove beyond the ledge which had captured the measured line in pursuit of the elusive bottom. The following day, Bowden, Exley, and Kristovich returned to Zacaton to attempt a more accurate plumb. The line spun off the reel, past 500′ past 800′, past 1000′! The weight finally stopped after some 1080′ had been measured.

The line was secured to the north wall of the ceynote and the divers completed plans to make a deep mixed gas dive the following day. In April 1993, Bowden dove to 504 ffw. and Exley to 721 ffw. Neither diver experienced performance difficulties or physiological complications during or after the dives. These two would be the first of seven sub-500 ft. dives made in Zacaton in a twelve month period. As the week of diving came to an end, Exley and Bowden agreed to return together to Zacaton, and like Hillary and Norkay, pursue the exploration of the depths of this upside down Everest. The apparent perfect site for an open circuit dive to 1000′ and beyond had at last been found. It was warm, there was no perceptible current, the natives were friendly, and access to the system was uncomplicated.

The goal was thus declared, that within the calendar year, a dive to obtain the bottom of Zacaton would be made by Bowden and Exley. Members of the Proyecto made six trips to Mexico during the ensuing twelve months. With each return, Bowden dove progressively deeper in order to prepare himself for the 1000′ attempt. Exley meanwhile pursued the exploration of a huge underwater cave at Bushmansgat, South Africa, diving  to 863′ in this system. During this dive, Sheck experienced visual, somatic, and neurological symptoms of high pressure nervous syndrome (HPNS). The symptoms resolved during his ascent to his first deco stop at 400 ffw. and there were no persistent effects.

In April 1994, the Proyecto, including Exley and Mary Ellen Eckhoff assembled on the Rancho Asufrosa. Two days were spent staging the required decompression bottles at their specified depths in Zacaton and El Nacimiento. The dive would be accomplished on independent descent lines, a condition both divers favored to avoid contact and potential interference during the very rapid descent. Each effort would be solo by necessity. Exley would use Heliair 6 as his bottom mix, Bowden, Heliair 6.4. Both divers carried an assortment of tables since the exact time of descent ( bottom time ) and maximum depth of the dive was unknown.

Both Bowden and Exley made multiple deep air acclimation dives to prepare themselves for the 1000′ attempt. Early in the morning on Wednesday, April 6, 1994, all was felt to be in readiness and the divers and their support team assembled on the banks of El Nacimiento. Bowden and Exley geared up and swam together through “El Pasaje” and into Zacaton. The pre-dive mood was positive and optimistic. The men began their descent at approximately 9:50 a.m. central standard time. Bowden dove to 925′ and would spend nine+ hours decompressing. Exley, for reasons we will probably never know, failed to return from his dive. He had reached a maximum depth of 906′.

At about the same time that Exley entered the water that morning, I was in California attending a Board of Directors meeting of the National Association of Underwater Instructors (NAUI). I had been elected Chairman of the Board only moments before when a phone message was relayed to me in the meeting. The caller explained that Exley, my longtime friend and diving collaborator, was missing and presumed lost in Zacaton.

I was stunned and speechless with the loss. It just didn’t seem possible to me that Sheck would not be coming back. Of all the divers I’d worked with on deep projects over nearly two decades then, Sheck was always the person whose opinion and perspective I most valued. I thought back to the reams of letters and notes we had exchanged over the years about dive plans, rigging, tables, and the analysis of fatalities of others we’d known. To hear that he was gone without a trace left me feeling like some part of me had been cut away. He was the most accomplished diver and technician I’d ever known.

Jim Bowden provides this account of that final day with Exley as they prepared for the 1000 foot dive.

“The time between December and April had passed rapidly with preparations and planning consuming every day and night. In addition to three sub-500 ft. dives, I made over 30 dives in excess of 300 ffw. Some were done on air to acclimate and build up my narcosis tolerance. Many of these dives included skills testing at depth, primarily problem solving questions or tasks posed by a colleague on mix while I was on air. It was essential that I be comfortable with an equivalent narcosis depth (END) of 330 feet. My bottom mix of heliair (69.5 He, 24.1 N2, 6.4 O2) called for an END of about 300 feet at 1000 feet. The bottom would demand that and more. I made one dive to 411 ffw on air, a record on air in a cave, but it was soon eclipsed by Sheck with his dive to 420 ffw on April 4th two days before our attempt for the bottom.

“Now was the time to fish or cut bait. The final preparations were made and the first support team left camp to put down decompression oxygen and my DiveComm full face mask that I planned to switch to at 20 feet. Shortly thereafter, we all left for the spring.”

Present on the day of the dive was the team consisting of Exley, Bowden, Mary Ellen Eckhoff (Exley’s ex-wife), Karen Hohle (Bowden’s wife), Ann Kristovich, and Marcos Gary. Press representatives included a writer and photographer from Sports Illustrated, a photographer from Destination Discovery, and a television film crew from Channel 7 of Tampico. Also in attendance was the land owner and his family along with many of the local residents of the area.

Bowden continues, “Sheck and I geared up and swam through the 600 foot passage, El Pasaje de Tortuga Muerte. to access our dive site. Surfacing in Zacaton, we swam slowly over to our descent lines. We commented on the beautiful day and wished each other luck. We separated at that time and went to our respective down lines. Time passed in silence as we calmed our breathing and focused our minds on what was ahead.

“After a time, I felt all was right and glanced over at Sheck. He seemed to sense my glance and nodded affirmation. I submerged and hesitated at 10 feet for a minute or so and then went into a free fall. I had planned a descent rate of one hundred feet per minute to 300 feet on air, then the same rate to 600 feet on heliair (50 He, 39.5 N2, 10.5 O2) and then switching to my bottom mix. I planned to slow my descent around 750 to 800 feet where I had first noticed the HPNS symptoms on my previous dive. All went according to plan. As I passed the 800 foot mark, I was conscious of very little tremor. I could just see Sheck’s light in the distance. It was the last I saw of him.”

However, at 900 feet Bowden was shocked to find that he had breathed far more gas volume than he had planned. His bottom mix cylinders contained barely more than 1000 psi. At that depth, his regulators could not deliver if the pressure dropped less than 500 psi. This was a big problem and Bowden had to deal with it quickly.

“I inflated my BCD wings and managed to stop my descent at 925 feet. I switched to the 80 cubic foot tank of bottom mix under my right arm and breathed that and then my travel mix back up to my first stop at 450 feet. By the time I got there they were both empty. To my horror, the regulator on my deep deco bottle free-flowed violently when I turned it on. It seemed to take a lifetime to shut it off again. I switched back to my back-mounted doubles to deal with the problem but I couldn’t fix the regulator. The only solution was to open and close the valve with each breath. I had eight minutes of stops between 350 and 300 feet where my next bottle was hung.”

Bowden could breathe easier when he made it to the fresh decom bottle with a properly functioning regulator. Now would come the really long decompression and the worry about oxygen toxicity and bends. Another switch to air at 260 feet would see him to 130 feet and a 30% oxygen nitrox mix. That’s when he knew something was wrong with Exley.

“At 130 feet, I relaxed. Here I could clearly observe the line that Sheck used on descent. All of his stage bottles were still neatly packaged and unused. The sinking feeling in my heart was overcome by the confidence that he had gone deeper than I had and was probably still below me.”

But on the surface, the support team already knew that Exley was in trouble. Ann Kristovich had watched the bubble paths of both men on the initial descent. Bowden’s bubbles disappeared at two minutes and Exley’s vanished a few seconds later as they both reached the deep ledge at 250 feet. Only one set of bubbles re-appeared after about 15 minutes and she couldn’t be sure if they were Bowden’s or Exley’s. Kristovich exchanged uneasy glances with Bowden’s wife, Karen Hohle. As planned, she then dived to meet Bowden at the 47 minute mark of the dive profile. She was relieved to find him but chilled to see Sheck’s stage equipment still hanging with no sign of him. The grim awareness of the situation gripped the pair.

Meanwhile, Mary Ellen Eckhoff was watching from the cliffs with no knowledge of the problem. She joined Hohle at the surface and was appraised of the scenario. Concerned, but not panicked, by the situation, she grabbed an extra decom bottle to take to Exley and swam down to encounter Bowden and Kristovich. Now her worst fears were becoming reality. She hastily scrawled on a slate, “I’m going to 250 to look for bubbles”. Dropping over the deep ledge, she could find no sign of Sheck or any bubbles coming from the depths.

Hohle had scrambled into her gear and caught up with Eckhoff. “I met Mary Ellen at about 100 feet on her way back up. She was crying and her mask was messed up. She wanted to go back to the surface but I grabbed her gauge and saw that it read 278 feet. I just held her. We stayed down for more than thirty minutes to get through the decompression. It as a very lonely time.”

Bowden was finally told that Sheck was lost as he reached his 60 foot stop. He felt himself grow numb from the loss and describes the remainder of his decompression as a mechanical exercise with little conscious thought. After a total of nearly ten hours, he surfaced but suffered a left shoulder DCS hit that then was treated with in-water therapy on the site. Bowden was now the first diver to successfully break the 900 foot barrier on self-contained scuba. His record depth of 925 ffw eclipsed Exley’s old 881 mark.

There was no consideration given to mounting a body recovery for Sheck since it was accepted that the only man capable of effecting such a recovery was the man who was already down there. Three days later while hoisting up the remainder of the equipment, Exley’s body was found. He had apparently drifted up from the deep cave passage and become entangled in the line. One of his tanks still had gas and his computer read 904 feet, suggesting that whatever trouble he had did not occur until about nine minutes into the dive.

The best educated guess would point to an HPNS incident. Exley had experienced a bad one in Africa that resulted in uncontrollable muscular spasms and multiple vision. This may have manifested again with more violent tremors that could have triggered an oxygen convulsion or simply made it impossible to negotiate gas switches as necessary. His death will remain a mystery and a tragic loss to the cave community.

As Sheck’s last dive partner, Bowden shares his thoughts, “I’ve been angered by unkindness and idle speculation by arm chair quarterbacks. And I have been touched by those who seem to understand and genuinely express sympathy without the need to pull something out of my soul. Much has been written in praise of Sheck and more will come. Ultimately, he will represent even more to us as history and recognized as the pioneer he truly was.

“I first met Sheck in Mexico in 1988 when he was making his then world record dive to 780 feet in Mante. Sheck sought my friendship as I did his for the same reason: we were loners. He did that with other explorers in all parts of the world. He was interested, humble and supportive of projects than many of “new age” cave divers didn’t even know existed. We had a common bond, an obsession, a passion… our love of exploration.

“Exploration was a demanding mistress that got in the way of our relationships with others and I now could cause a lot of pain to those who loved us. We could spend most of day on a project without even talking to each other. Our personalities were direct opposites. He was the most disciplined man I have ever met with a brilliant calm intellect. Karen and Ann have both said that we looked like little boys who found the greatest treasure on earth when we realized that Zacaton was the ultimate world class deep system. I do believe that we both were never more alive than in those moments of trial in virgin space.

“Mexico loved him. He truly respected their culture and ways. The rural poor of Mexico have a remarkable ability to judge courage, honesty, and sincerity. The only time I allowed myself to succumb to emotion during those days of our loss and the recovery was when I walked to the edge of Zacaton and saw the simple cross and flowers put there by the people of el Nacimiento and Higeron.

“Sheck met life head on, with few misconceptions. Only death deceived him, taking him by surprise. I will miss him very much, but then we always dove alone anyway. Perhaps now he will be with me more than ever.”

Exley’s loss shocked and saddened the entire world community of diving explorers. To this day, he is considered as the foremost leader in both cave diving and mixed gas diving techniques. He truly led the way and others followed in his footsteps.

Bret Gilliam
54 Stonetree Rd.
Arrowsic, ME 04530

direct phone (24 hrs.) 207-442-0998
cell phone 207-841-0998

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5 comments for “ZACATON: The Tragic Death of Sheck Exley

  1. William W. Smith
    January 13, 2016 at 4:28 am

    Make no mistake that Exley is the Master we all have followed…

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  2. Paul Thacker
    August 15, 2015 at 5:40 pm

    Thank you for the article. I am a 56 year old recreational diver, hobby level only, who is fortunate to have had the honor of meeting Sheck back in the 1990′s. I was then employed at Jacksonville Welding Supply, in Jacksonville, FL, where he would occasionally bring tanks in to have filled at what was then our Union Carbide Specialty gasses facility. I looked forward to his visits. He was always upbeat, and willing to share a quick story about his recent adventures or upcoming endeavors. The last time I saw him was just before his death, and he told me how he was headed down to Mexico for the record attempt. I can still remember the shock of sitting down in front of the TV only days later, and hearing the news anchor announce that tonight’s big story was “local diving legend dies in record attempt in Mexico”. I can’t say I new him well, but I can tell you he seemed like a great guy, and I’m sure he is missed by everyone who had the privilege of knowing him, as well as the diving community as a whole.

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  3. bret gilliam
    February 17, 2014 at 7:31 pm


    Your comments are right on. And Sheck had earlier displayed a problem with HPNS on other dives including one in Africa on his most recent prior expedition. Both Bowden and I think it was likely that he may have deliberately wrapped the descent line around part of his body when the tremors ensued as a way of recovering once they passed. His entanglement is the only reason his body was retrieved. And Sheck was not one to fall victim to such a situation unless he made a conscious decision to use the line as a “last chance” maneuver.

    A great guy… sadly missed by all.


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  4. Daniel J. Vale
    February 17, 2014 at 3:34 pm

    It seems likely from the details of this report that Mr. Exley did encounter problems with hpns on his fatal dive. I reached a depth of 733′, but in a saturation diving system environment – it took us a little over 4 hours to reach that depth, & none of the dive crew experienced the slightest hint of hpns.The rates of compression on the described dive were, by necessity, much, much faster than those experienced in a saturation exposure, thus the likelihood of experiencing hpns on the described dive was much greater. It is also true that, experimentally, deep saturation diving exposures met the problem of hpns much deeper – around the 1800′ mark. Various inert gases were introduced into the mix to try & mitigate the affects of hpns, with some success; however, the obstacles for diving below 2000′ were considerable, and with the advancement in the development of rov’s, deep-manned saturation diving research was curtailed around the 2200′ mark, I believe. There is also the factor of individual susceptibility to hpns to be considered. It appears from the story that Mr. Exley might have been less physiologically tolerant of rapidly increasing ambient pressures/breathing gas density, than was Mr. Bowden. I’ve seen similar variances in personal susceptibility to dcs during my years in commercial oilfield diving. On jobs where we were making repeated exposures to the same depth, some guys were getting bent. With all dive variables being essentially the same, we surmised that individual tolerance might have been the difference.

    In any case, the technical expertise & courage to attempt such exploratory dives with scuba equipment is extraordinary, to say the least. Mr. Exley will always be remembered for his contributions, his amazing skills, and most of all, his overwhelming need to explore.


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  5. Sonny jones
    December 3, 2013 at 12:05 pm

    I had the privilege of knowing Sheck and Mary Ellen. Sheck also had a great love for flying general avaition airplanes and personally owned a Cessna 172 which we rode together Lon occasion. I heard of his diving but did not know the depth to which he was world known. I was able to enjoy the flying side with a friend. Yes, he is missed today as I continue to fly. Sonny jones, live oak, fla.

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