The Shaft sinkhole can be located 3km West of Allendale East and 2km South West of Mount Gambier, also known as Cave View on th eproperty.
Reference Number: Cave Exploration Group of S.A. Cave Number L158

CDAA Category:

The cave is rated by the CDAA as a Sinkhole, but certain conditions apply.
These include:
No Nitrox in diving mix
Decompression mixes must be attached to a shot line.
Proof of 5 twin tank dives are required.

Unlike all of the other large waterfilled caverns of the surrounding area, The Shaft has a relatively short history. This is due to it's small entrance which was not discovered and did not even exist until 1938. At this time the surrounding land was owned by the late Mr.C.Griffin who lived a half mile West of Allendale.
Mr.Don Kerr who is Mrs Ashby's father was ploughing in a flat featureless paddock when one of his horses stumbled for no apparent reason, Upon investigation Mr Kerr found to his amazement that the horse had punched a 12 inch diameter hole into the soft topsoil to reveal a cavern below. 

With the help of two neighbours he dropped a line into the sparkling clear water which he could see below. It would of been an incredible moment for three individuals after discovering that the line fell and could not be felt until 150 feet (45m) of line had been played out. The water surface was 18 feet (5,5m) below the cavern entrance but did not indicate such a large and deep resovoir of water lay below. After calculations this would equate to a depth of 132 feet or (40m) which is certainly surprising considering the small size of the entrance.
They may of only expected a few metres of water depth like many of the small shallow split caves found in the area which only just penetrate the water table. No doubt Mr Kerr was satisfied that no one would now fall into the deep hole or any of his lifestock.

After raising the weighted line to above the water surface, they swung it in a pendulum motion until it hit the roof, finding it to be a large chamber. The weight itself when removed was found to be coated in a white lime similar to plaster used to top coat house walls.

In 1953, the property was purchased by Mr and Mrs Ashby from the Griffin family and the cave remained virtually unchanged until around 1965, when the old house was demolished and the rubble disposed of into the cave. Some of this material can be seen today amongst the limestone rocks cleared from paddocks and dropped into the entrance hole to make up the introduced rockpile.
Around this time in the mid 1960's local divers began to explore many of the caves and sinkholes of the region and this was when "The Shaft" was first dived.

The Mount Gambier Spear Fishing and Skin Diving Club heard rumour about the shaft and as they were on there way to Ewens Ponds they decided to drop on over and have a look for themselves.
By this time the surface entrance had enlarged through erosion of the top soil and was clearly visible, The hole today has a 1 metre diameter vertical tube which opens into a chamber with water directly below.
When they arrived the only diver with scuba equipment on site was "Jock" Huxtable who had only 700 psi (4700KPA) of air in his tank. He was lowered into the cave by a rope held by many of the dozen or so people present and then he dived to a depth of 70 feet (21m) and returned to report that the cave continued.

It wasn't long before other local divers started to visit the hole which was named "The Shaft" due to the brilliant shaft of light which was produced by the small roof entrance and which penetrated the clear water to great depths. Many hundreds of divers occurred and the cave's reputation for transparent water and depth began to spread.
On the 28th May, 1973 a group of eight New South Wales divers entered "The Shaft" to undertake a dive to greater than 60M depth where they intended to take photographs of themselves. Sadly only four of the eight divers safely returned as a terrible tragedy occured.
Media reaction to this tragedy (equaled only by a similar accident in America several years earlier) was to say the least, irresponsible. All sorts of false accusations and emotional rather than factual statements were made.

The Shaft - Mount Gambier

The event was also drawn out because even three months later, at the Coroners Inquest none of the bodies had yet been found. Even so , the Coroner found that all four divers had drowned due to lack of experience in this type of diving and general lack of heedance of recognised safety standards. It was not until 10 months later that all the bodies were finally recovered.As a result of this accident many of the landowners chose to close their access holes to divers as a way to prevent more fatalities. Subsequently the CDAA was formed in September of 1973 as a "self regulatory body of cave divers and in a relatively short space of time most sinkholes were once again available to divers.

During the late 1970's the bore to the North of the entrance was sunk but unfortunately it missed the edge of the main chamber by quite some distance. It eventually pierced the roof at a depth of 46m, only 4m from the cave's known extremity.

The Shaft Study - CDAA Research Group (1984)

This indepth article explains what happened to the eight divers that entered "The Shaft" on Monday, 28th May 1973. 

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The Hranice Abyss (Czech: Hranická propast), the English name adopted by the local tourist authorities, is the deepest flooded pit cave in the world. It is a Karst sinkhole. Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. The cave can be located near the town of Hranice (Prerov District). The greatest confirmed depth as of 27th September is an incredible 473m (404 m under the water line, This staggering depth makes Hranice Abyss the deepest known cave in the world. Moreover the expected depth could be greater than 1200 m. The Hranice Abyss was created by a collapse of the cave roof, which was eaten away by warm carbonic acidulous spring water in limestone.

Access to the underwater part of the cave which is located 300km (186 miles) east of Prague, is inside a gorge nestled within a forest.
Krzysztof Starnawski, a Polish diving expert has been exploring the cave since 1997. Mr Starnawski has extensively explored the caves including finding a narrow opening 200 metres down, which led to him lowering a probe through the sharf to a depth of 384 metres.Describing the exploration, he told National Geographic last year: “It was amazing, because it meant that we had found the deepest cave on Earth. 

“But the most important thing that we saw on the camera was the continuation of this cave. That means we haven't finished this project—not yet. We finished only one part: crossing the 400-meter mark that we had set for ourselves four years ago.” The cave is so deep traditional scuba divers with rebreathers would never be able to reach the bottom of the cave without certain death. This cave has not been fully explored but at this time it is 39 feet deeper than the previous record holder for deepest cave. The Pozzo del Merro located in northeast of Rome was the worlds deepest.

Krzysztof Starnawski

The discovery came on Sept. 27, when a remotely operated vehicle (ROV) deployed by a Czech-Polish expedition plunged to the cave’s deepest regions and took a reading with its on-board depth gauge, according to National Geographic, which helped fund the expedition.  The September voyage wasn't Starnawski's first mission to Hranicka Propast. He first traveled there in 1999. In subsequent trips, he released probes through a narrow squeeze passage to determine its depth.In 2014, his probe stopped just short of the previous record holder's depth at 384 meters. Last year, he returned to find the squeeze passage had collapsed and could lead deeper still. This year, the probe successfully discovered new depths: The rov could go no more after maxing out its teather line even so the bottom was no where to be seen.

Polish explorer Slawomir Packo explores the Hranicka Propast - In this underwater photo taken Aug. 15, 2015 in the flooded Hranicka Propast, or Hranice Abyss, in the Czech Republic Polish explorer Slawomir Packo is exploring the limestone abyss and preparing for deeper exploration with the use of a remotely-operated underwater robot.

"The dive on September 27 was one in the long series of dives that I did in the last 20 years in Hranická Propast. They all had the same goal: to explore the cave further and deeper. As the expedition leader for the last several years, I've prepared the equipment and the route in and out for the ROV’s dive, so the ROV could go beyond the limits of a human diver, and get through the restricted passage and between the fallen logs and trees."Starnawski says they used an ROV to reach the maximum depth, and the robot held the most important part of the push. According to him, he dived down to 200 meters to pave a new line for the robot to follow. Then they sent the robot down, as deep as its possible, and recorded 404 meters. "I invited Bartlomiej Grynda from GRAL Marine, with his custom-built ROV, to send the robot as deep as possible to explore the cave. The results were astonishing. The goal was to give the ROV a good start from there to the deepest part of the cave. I came back to the surface, and then we went down with the robot to a depth of 60 meters (197 feet). From there, the team at the surface navigated it, via fiber-optic cable, down along my new line to 200 meters deep. Then it went down to explore the uncharted territory—to the record-breaking depth of 404 meters."

404 Floor not found

Starnawski could not celebrate after his dive as he was suffering from decompression sickness and he had to spend two to four hours in the hyperbaric compression chamber. Starnawski came prepared. He read laminated books during his stay and enjoyed crime stories and political thrillers. The decompression chamber was sunk beneath the surface to allow Starnawski to adjust back to the correct body surface pressure. He thinks that the cave was formed by carbon dioxide-laden water bubbling up from below and gradually wearing away at a natural fault in the limestone.The ROV revealed trees and logs at the bottom of the cave, something that he says should be impossible given the cave’s current configuration. The recent rockfall that allowed him to access deeper portions of the cave backs that theory up.Hranická Propast took the record from an Italian cave called Pozzo del Merro, previously assumed to be the world’s deepest. That cave was measured to be 1,286 feet deep, just 39 feet short of the record.

Hranická Propast s CCR Inspiration - video z roku 2004

While Hranická Propast may hold the record for now, new caves are being explored all of the time. Indeed, the Italian cave may prove to be even deeper — the expeditions in Pozzo del Merro discovered a horizontal chamber at the presumed bottom, out of reach of their ROV’s cable, which could lead to new discoveries. In other words, this record may not stand for long. Starnawski dedicated several years of preperation for the dangerous dive, He say's while humans get the credit for this discovery the record breaking cave dive was achieved by a robot.The Hranice Abyss is not only the deepest known cave in the world, but also one of the most unusual. Most aqua caves are formed by rain or groundwater falling downwards onto soft limestone layers, causing erosion over periods of geological time. This cave, however, was formed by heated mineral-rich waters rising from geological activity within the Earth’s mantle. There are probably only three caves like this in the world. There is nothing typical about this cave, and every dive we make new discoveries. What could lie at the true bottom of the Hranicka Propast only time will tell.

Sheck Exley born (April 1, 1949 - Died April 6, 1994 was an American cave diver. He is widely regarded as one of the pioneers of cave diving, and he wrote two major books on the subject: Basic Cave Diving: A Blueprint for Survival and Caverns Measureless to Man. On February 6, 1974, Exley became the first chairman of the Cave Diving Section of the National Speleological Society.  During his career, he established many of the basic safety procedures used in cave and overhead diving today. Exley was also a pioneer of extreme deep scuba diving.For purposes of rescue during cave diving, Exley helped standardize the usage of the "octopus", a redundant second stage diving regulator that can be used as a backup in the event the diver's primary second stage fails, or alternatively, to allow the diver and his buddy to have simultaneous access to the diver's gas if the buddy has an out-of-gas emergency. The octopus is now considered an essential piece of equipment among virtually all scuba divers, whether caving or in open water.

He died at age 45 while trying to set a depth record by diving the world's deepest sinkhole, Mexico's 1,080-foot (330 m) deep, Zacaton a fresh water cenote.Exley began diving in 1965 at the age of 16. That same year he entered his first cave and was hooked on cave diving for the rest of his life. To finance this passion, Exley worked as a mathematics teacher at Suwannee High School in Live Oak, Florida.In spring 1973, Exley served as an aquanaut during an eight day mission aboard the Hydrolab underwater habitat in the Bahamas.

180 scientific missions were conducted aboard Hydrolab in the Bahamas. The missions in the Bahamas which were chronicled in the Hydro-Lab Journal, were funded by the Perry Foundation.

2016-03-30 - Hydro Lab, Grand Bahama

Exley was the first in the world to log over 1000 cave dives (at the age of 23); in 29 years of cave diving he made over 4000 dives. Exley had an unusual resistance to nitrogen narcosis, and was one of the few divers to survive a 400-foot (120 m) open-water dive on simple compressed air. In acting as a safety diver for two divers trying to set an air-only depth record in 1970, Exley reached 465 feet (142 m) in salt water, but could go no deeper due to narcosis and the start of blackout (the two record-depth attempting unconscious divers died just out of reach beneath him, and such air-depth records are no longer sought or recorded). During his diving career, he set numerous depth and cave penetration records. Exley is one of only eleven people in the history of technical SCUBA diving to dive below 800 feet (240 m), as well as the first. His carefully planned multistage decompressions from these dives, in open water (not in a decompression tank), sometimes required times of as much as 13.5 hours. However, he never suffered a classic case of decompression sickness in his career. Exley and German cave diver Jochen Hasenmayer became friends and rivals in the 1980s, each repeatedly attempting to break the depth records of the other. 

This film is a tribute to legendary cave explorer Sheck Exley prepared for the 50th anniversary of his story "Lost in the Slough", one of Sheck's most miraculous dives. Through re-creation and investigation, we rolled back the mysteries and uncovered details missing for 50 years that put this story on par with any classical tale of yore. In this case, a teenage boy takes on an underwater labyrinth completely devoid of light and air. The cave teaches him the discipline of the guideline by hiding the real exit while providing him with a false one that sends him into a primal struggle for survival. In the end, he escapes through dogged determination but also because he had unconsciously reserved enough air to find a new exit.

Zacatón (El Zacatón sinkhole) is a thermal water-filled sinkhole belonging to the Zacaton system - a group of unusual karst features located in Aldama Municipality near the Sierra de Tamaulipas in the northeastern state of Tamaulipas, Mexico. It is considered one of the deepest known water filled sinkholes in the world with a total depth of 339 meters (1,112 ft).Using an autonomous robot, the underwater portion of Zacatón has been measured to be 319 metres (1,047 ft) deep (a 20-metre (66 ft) difference between the rim of cliff and surface of water adds to the total depth). Zacatón is the only sinkhole of the five located in Rancho La Azufrosa to have any noticeable water flow.The name Zacatón comes from the free-floating islands of zacate grass which move around on the surface with the wind.Scrapings from the rock walls beneath the surface yielded at least three new phyla of bacteria.

Dr. Ann Kristovich set the women's world depth record of 554 feet (169 m) during a 1993 dive into the sinkhole.
On April 6, 1994, explorer diver Jim Bowen and cave diving pioneer Sheck Exley entered El Zacatón with the intent of reaching bottom. Bowden dived to a men's world record depth of 925 feet (282 m), but Exley died, probably from high pressure nervous syndrome (HPNS) at a depth of 879 to 906 feet (268 to 276 m).
The NASA Deep Phreatic Thermal Explorer (DEPTHX) project used the sinkhole as a testbed for robotic hardware being developed to explore the Jovian Moon of Europa. Zacatón is just one of the numerous sinkholes and other karst features in the region. Here are located more than 15 sinkholes, several cave systems and karst springs with caves. Several of these karst features have unusual characteristics like travertine lids over several of the sinkholes with isolated waterbodies below.

Marcus Gary, Bill Stone and others use DEPTHX, the world's first cave-diving robot to explore one of the world's deepest water-filled sinkholes, Cenote Zacaton, in northern Mexico. Excerpt from "This Week @ NASA" program broadcast in spring 2007.

The NASA Deep Phreatic Thermal Explorer (DEPTHX) The Deep Phreatic Thermal Explorer (DEPTHX) is an autonomous underwater vehicle designed and built by Stone Aerospace, an aerospace engineering firm base in Austin Texas. It was designed to autonomously explore and map underwatrer sinkholes in northern Mexico, as well as collect water and wall core samples. 

Since the late 1990s, Dr. Marcus Gary, a hydrogeologist at the Edwards Aquifer Authority and adjunct professor at the Jackson School of Geosciences, University of Texas at Austin. has studied Sistema Zacatón to understand how the sinkholes formed and how they evolve over time. During these studies, Gary made extensive use of a number of investigative tools, including those on the DEPTHX probe, geophysics, isotope geochemistry, field mapping, and geomicrobiology. Gary was a primary member on the DEPTHX mission, which used an autonomous underwater robot to explore the deepest parts of Zacatón for the first time. According to Gary, these sinkholes began to form during the Pleistocene. (Pleistocene is often referred to as "The Ice Age" which lasted from about 2,588,000 to 11,700 years ago) - as a result of volcanic activity from below. In his scientific equation, Volcanism turned deep water slightly acidic by adding dissolved carbon dioxide and hydrogen sulfide, This water slowly dissolved the limestone above, creating porous karst. This is referred to as “hypogenic karstification.” From time to time, overlying rock collapsed into hollow chambers below, creating deep shafts. If his interpretation is correct, Sistema Zacatón has more in common with "Mammoth Hot Springs" in Yellowstone than with other deep sinkholes in this same region of Mexico.

Europa (Jupiter II) is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei and was named after Europa, the legendary mother of King Minos of Crete and lover of Zues (the Greek equivalent of the Roman god Jupiter.
Slightly smaller than Earth's moon, Europa is primarily made of silicate rock and has a water-ice crust, and probably an iron nickel core. It has a tenuous atmosphere composed primarily of oxygen. It's surface is striated by cracks and streaks, whereas craters are relatively rare. I n addition to Earth bound telescope observations, Europa has been examined by a succession of space probe flybys, the first occuring in the 1970's.Europa also has the smoothest surface of any known solid object in the solar system. The apparent youth and smoothness of the surface have led to a hypothesis that a water ocean exists beneath it, which could conceivably harbour extraterrestrial life.

Hydrogeologist Dr. Marcus Gary, stands next to the (DEPTHX)

Zacatón (El Zacatón sinkhole) is a thermal water filled sinkhole belonging to the Zacatón system - a group of unusual karst features located in Aldama Municipality in the northeastern state of Tamaulipas, Mexico. It is the second-deepest known water-filled sinkhole in the world with a total depth of 339 metres.

Another interesting hydrogeologic feature is that some of the sinkholes appear to be in the process of closing up at the top as crusts of travertine (a form of calcium carbonate) form at their surfaces. Marc Airhart, a science writer at the Jackson School of Geosciences wrote:
It’s a bit like the skin on a can of paint that has been left open in the sun. For the paint, it might take a day or two. In this case, the process probably takes thousands of years. It is basically the sinkhole’s way of taking a bunch of dissolved rock floating in the water and recycling it to form new rock at the surface. At least one sinkhole (Poza Seca) appears to have closed up entirely, sealing off an underwater lake, possibly with unusual life forms. If such life forms exist, they’re likely to be bacteria that can live without oxygen and sunlight. And assuming the lake has been sealed off from the outside world for thousands and thousands of years, they might have evolved to be different from anything scientists have ever discovered and characterized before.

Zacaton Sinkhole

“Every field of human endeavor from Tidily Winks to space exploration has its champions and its marks for human endurance and achievement. Without them there would be little or no human progress for we would have nothing to measure our efforts by or encourage us to try harder. It is difficult to imagine any aspect of our lives that is not enhanced by competition, the drive to excel and the recognition of excellence.” 
Sheck Exley
Caverns Measureless to Man.

A Tribute - By Jim Bowden

By Jim Bowden
Mexico, April 6, 1994. Sheck Exley, my mentor and friend, and I were prepared to dive deeper than anyone has ever dived independent of submarines or commercial habitats. Sheck never returned.

Was it worth the risk of loosing the world’s greatest dive explorer to go deeper than any other man on scuba? It is easy to question the value of any endeavor when a death occurs. When Chris Bonnington, mountain climber and author of Quest to Adventure, was asked if the deaths of friends and acquaintances in climbing accidents had ever led him to question the value of his sport he answered, 

“No. Because you know . . . . climbing is dangerous. . . .
 

Jim Bowden is an American technical diver, In 1994 he set a world record, since broken, by diving to 925 feet (282 m). He has also made six sub-five hundred foot dives, more than any other diver on record.

You know that risk is an inherent part of the game. So you have got to accept it. It does not reduce your sadness at the loss of a friend. The tragedy is not for the person who got killed, it is for the wife, the girlfriend, the children and parents. It is the people very close to that person who are bereaved and lost and left without him. The individual who gets killed has had a full life. He has gone out right on top, doing something he enjoys doing. The tragedy is within the survivors.”

So it has been with Sheck’s death. I still feel a terrific sense of loss because I enjoyed his company, his passion and his craft. It is my loss, however. I believe that he was never more alive than in those moments of trial in virgin space. It is easy to die. It is very hard to live. Sheck met life head on, with few misconceptions. Only death deceived him as it eventually does us all. Even then, during our “year of living dangerously” that we spent preparing for our dive, he addressed the consequences of the myriad dangers we faced. His eyes were wide open. Never did he make light of the risk, but it was important for him to make the dive. It was personal. He already had the record. Still he had to go deeper, not to make the record unbreakable, but for his need to achieve as much as he could. He had to go deeper for himself 

Exley with Jim Bowden after making a 400-foot air dive at Zacaton

I first met Sheck in 1988 when he was making his world record dive to 780 feet / 237 M in Nacimiento Mante, another deep spring in Mexico. He was alone in that great beautiful system. His support team of three was waiting his return. In this egomaniacal discipline of cave diving, it was refreshing to see a man accomplishing the impossible without the fanfare and entourage that we so often see in much lesser endeavors. Perhaps the bond we formed as dive partners was because so much of our diving history had been solo. We worked together, but the dive was our independent effort. Space and time separated our major efforts. We needed the focus that comes from being independent of others and masters of our own destiny. 

Sheck took little advantage of his fame as the deepest diver. He was a modest individual, a gentleman; respectful of his colleagues and fellow cave explorers, both wet and dry. It is an unfortunate truth that the greater your accomplishments, the greater the opposition and animosity. Still, I cannot remember him ever saying a bad word about anyone. There are so many critics with an acute case of the Jehovah Complex, wanting to save us all from ourselves. I am sure that he had reservations about some of his critics and the bad manners that seem to be so much a part of the cave diving community, but he would softly say, “They are probably better divers than I am” and let it go at that. I am reminded of Mark Twain who said, “Indecency, vulgarity, obscenity — these are strictly confined to man; he invented them. Among the higher animals there is no trace of them.” Sheck was, indeed, a higher being. 

Sheck Exley tests the Cis-Lunar MK1 prototype rebreather, December 11, 1987. Weighing a whopping 205 pounds (93 kg) the unit was not considered "portable" and had to be wheeled into the spring on a dolly, yet underwater it was neutrally buoyant. The unit had outrageous range and was also fully redundant, meaning it contained two complete rebreathers within the one backpack. Shortly before this dive Bill Stone used the rig to conduct a 24-hour dive in Wakulla Basin. Only one half of the rig was used for this dive, meaning that a 2-day underwater mission could have been carried out. This was the first rebreather to utilize multiple, redundant computer systems for electronic control of the life support backpack. It was also the first rebreather to use lithium hydroxide to remove carbon dioxide from the breathing loop and contained novel concepts to permit the safe use of that material.
[photo �1998 Wes Skiles]

Perhaps the greatest complement to an individual’s lifetime of accomplishments is in the respect of his peers. The best diving champions in the world still mourn Sheck. Some of these individuals, like Olivier Isler, were and still are deeply saddened by his absence. What a wonderful legacy because I believe, as Sheck did, that Olivier is the greatest cave diver in the world today. Interesting enough, he too, is a solo actor in his great accomplishments.

Recently I made a trip to Zacaton to check the water conditions before we mounted a major effort. Standing alone, waist deep in the waters of El Nacimiento, the spring entrance to El Pasajae de Tortuga Muerta and beyond to Zacaton, I noticed that the day was unsettled, stormy, windy, like the day Sheck died. The winds were blowing the palms and gusts swirling in that massive system moved the grass islands like relentless behemoths. I was alone this time, and although I had traversed the cave so many times in the last several years, I found this reminder evoked more emotion than I anticipated. We had such plans to follow our successful dive to the bottom of Zacaton. There were so many places we wanted to dive around the world. This too is my loss. I may yet dive those exciting virgin places but I cannot dive them with Sheck. 

Some years ago I selfishly dedicated my life to live my dreams and to never put off the opportunities that are so often relinquished because of perceived obligations and responsibility. When we were invited to go to South Africa and dive Bushmansgat the summer before our dive in Zacaton, I declined, knowing that I needed to train and that we had a deeper system over here. Besides, I was sure that the future held great promise for us to dive exotic and exciting systems in Yugoslavia, Namibia and other we places we plan to dive after Zacaton. Not joining him in South Africa was a contradiction to my pledge. I put off something dear for another day that will never come. 

This tribute to Sheck has been a difficult task for me. I chose to try and show the spirit he possessed rather than to simply chronicle his many achievements. Those achievements are indeed grand, but it was his passion that made them possible. He was an inspiration to us all because of his spirit and passion for his craft. He was a banner for the individual and what one man could accomplish, often against great odds. Historically it is one individual’s pioneering breakthrough that leads the rest of us out of the trees. And they often pay a tremendous price for the boon we receive.

Sheck still dives with me on every dive I make. He is discussed around the campfire as if he were still here. I am not a religious man, so immortality to me is in the memories of our friends, the worth of our work, the legacy of gentlemanly conduct and the inspiration that will drive future efforts to accomplish the impossible. Sheck said one night in our camp in Mexico that the greatest complement to a teacher is to have his students go on to surpass all their teacher’s accomplishments, to go to greater heights in life, and I would suppose, to greater depths.

Sheck died aged 45 on April 6, 1994 while attempting to descend to a depth of over 300 metres (1,000 ft) in a cenote called Zacatón in Mexico.

He made the dive as part of a dual dive with Jim Bowden, but Bowden aborted his descent early when his gas supply ran low. Exley’s body was recovered only because he had hooked his arms in the descent line, perhaps to sort out gas issues.

His wrist-mounted dive computer read a maximum depth of 268 metres (879 ft). It is not certain what caused his death; team members concluded the causes “…could include stress of HPNS exacerbated by the narcotic effects of nitrogen at that depth”.

Sheck Exley. Photo © Michael Menduno

The line was also wrapped (deliberately) around Exley’s tank valves. Bowden and other experts have theorised that Exley may have done this in anticipation of his own death to prevent any dangerous body recovery operations.

Sheck Exley is one of only eight people in the history of technical SCUBA diving to dive below 800 feet.”

Into The Blue Void

And so, on April 6, 1994, two of the world’s most skilled extreme deep divers plunged into the dark, murky waters of El Zacaton. 
Suffice to say that Bowden and Exley were both determined to reach the 1000 ft milestone. This was their descent; their Mount Everest. The proportions were staggering: if you were to place the Trump Building, inside El Zacaton, it would completely disappear. And thus began their descent into darkness.

After eleven minutes, Bowden had reached 898 feet when he noted that his gas reserves were lower than expected. Deciding to abort the dive, he ascended, going through a 9-hour decompression period.
Exley went on, the water so dark that he never knew of Bowden’s decision to abort. He would remain alone to the very end.
18 minutes into the dive, one of the safety divers, closely watching the bubble stream of both divers, noticed that Exley’s stream had stopped. What followed remains one of sport’s greatest mysteries.Exley’s wife, Mary Ellen, descended to 279 feet to verify if the flow of bubbles had been diverted by some obstructions or ledge but they had not.

El Zacaton had taken a singular human life and left very few clues.
What happened to Sheck Exley during those 18 minutes?
Typically, a demise of a solo diver, under such adverse circumstances, left very few leads to go on. The people that knew Exley were certain of one thing: he did not panic.
Cave diving is to open-water scuba as flying an F-16 is to piloting a Cessna, and Exley was the ultimate definition of grace under pressure, even under the most harrowing of circumstances.
As if to defy El Zacaton’s deadly clutches, three days later, Exley’s body was recovered when the guideline was pulled from the cave.

What the rescue team saw left them speechless: Exley’s body appeared to be wrapped intentionally with the guideline, around his arms and valves of his dive tanks.
His dive computer read a depth of 879 feet.
It is speculated that Exley, seeing his imminent death, proceeded to do this in order to prevent any rescue attempts. At these depths, it would be suicidal.

It was also concluded, after a careful analysis of the incidents leading to Exley’s death, that he probably suffered from HPNS (oxygen-induced tremors and incapacitating).
For reasons which remain unknown even today, Exley’s primary dive tanks became depleted sooner than calculated. It is conjectured that he had to switch to his “travel mix”, clearly not suited for such depths, exacerbating an already dire situation.

It is also believed that he also tied the surrounding guideline to stabilize a failed ascent attempt. His BCD (Buoyancy Control Device) was unable to fill with air from his “travel mix”, making things even worse.
At some point, many experts believe, Exley lost consciousness, eventually leading to his death.
One thing that everyone who has studied his untimely death is that there is no single factor that leads to tragedies like these, but more likely, a series of disastrous events.

Exley’s Blueprint for Survival, which listed his ten recommenda­tions for safe cave diving:

1) Always use a single, continuous guideline from the entrance of the cave throughout the dive.

2) Always use the ‘third rule’ in planning your air supply.

3) Avoid deep diving in caves.

4) Avoid panic by building up experience slowly and being prepared for emergencies.

5) Always use at least three lights per diver.

6) Always carry the safest possible scuba.

7) Avoid stirring up the silt.

8) Practice emergency procedures with your partner before going diving, and review them often.

9) Always carry the equipment necessary for handling emergencies, and review them often.

10) Never permit overconfidence to allow you to rationalise violating safety procedures.

Bowden explains his descent in Zacaton, 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 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 time I saw him.

Extract taken from - Basic Cave Diving– A Blueprint for Survival” by the cave diving pioneer, Sheck Exley.

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.
Bowden inflated his BCD wings and managed to stop his descent at 925 feet. He then switched to the 80 cubic foot tank of bottom mix under his right arm and breathed that and then his travel mix to get back to his first stop at the 450 feet mark. He say's 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 could not fix the regulator issue. The only solution now for me 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 the bends. Another air switch at 260 feet would see him to 130 feet and a 30% oxygen nitrox mix. That's when he knew something was wrong with Sheck.

At 130 feet, I relaxed, Here I could clearly observe the line that Sheck used on descent, All of his stage bottles were still nearly 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 below me.But on the surface, the support team already knew that Sheck was in trouble, Anne Kristovich had watched the bubble paths of both men on the initial descent. Bowden's bubbles disappeared at two minutes and Sheck'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 Sheck'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 Sheck 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 feet to look for bubbles" Dropping over the deep ledge she could find no sign of Sheck or any bubbles coming from the depths.

1981-11-22 Sheck Exley geared up in front of white and blue van. Photo courtesy of Mary Ellen Eckhoff ...

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 30 minutes to get through the decompression. It was a very lonely time. Bowden was finally told that Sheck was lost as he reached his 60 foot step. 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 ten hours, he surfaced but suffered a left shoulder DCS hit that then was treated with in water therapy on site, Bowden was now the first scuba diver to successfully break the 900 foot barrier on self contained scuba. His record depth of 925 ffw eclipsed Sheck's old 881 mark.

Nuno Gomes dives to the deepest point of Bushmansgat Cave in South Africa with the assistance of his team. The cave is 1550 m (5000 feet) above sea level

There was no consideration given to mount 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, Sheck's body was found. He had apparently drifted up from the deep cave passage and became entangled in the line. One of his tanks still had gas and his computer read 906 feet, suggesting that whatever trouble he had did not occur until about nine minutes into his dive.
The best educated guess would point to an HPNS accident. Sheck 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 of 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.

Bowden 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 for the same reasons, We were loners, He did that with other explorers in all parts of the world. He was interested, humble and supportive of projects that many of "New Age" cave divers didn't even knew 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 a 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 truely respected their culture and ways. The rural poor of Mexico have a remarkable ability to judge corage, 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.

Native Americans and Canarians participate in the El Nacimiento rehearsal in Main Plaza.

Sheck met my life head on, with a 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.
Sheck Exley's death and 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 for others to follow in his footsteps.

Sheck joined Jim Bowdens exporation team in 1993 for a week, He and Bowden used "Air Dives" to produce a 258ft drop by Bowden and 407ft by Sheck but no bottom was in sight. Both divers dove beyond the ledge which had captured the measure 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 feet, past 800 feet, past 1000 feet ft! The weight finally rested at a measured depth of 1080 feet.

The placid and still sinkhole El Zacaton

The line was secured to the north wall of the ceynote and the divers completed plans to make a deep mixed gas dive the next day. In April of 1993, Bowden dove to 504 ffw and Exley to 721 ffw. Neither diver experienced performance difficulties or any psychological complications during or after the dives. These two divers would be the first of seven sub 500 feet 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 to continue there exploration of the deep system. They considered Zacaton the most perfect site for an open circuit 1000+ feet dive had at last been found. Like David Shaw who dived Bushman's hole in South Africa that system has a depth of 927 feet (282.6 metres) Gas mental and physical problems are extremely likely at those depths and Zacaton was deeper at 1112f. When the weight depth test was initiated a depth of 1080 feet was recorded but obviously the weight did not fully reach the gradiented max bottom or even corrosion can slowly over time increase maximum depth.

The goal was now in mind and both divers declared they would before the year was out attempt a deep dive to the bottom of the system, 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 immensly dangerous and technical dive to 1000 feet+. Exley meanwhile pursued the exploration of a huge underwater cave at Bushmansgat South Africa diving to 863 feet. During the dive however Sheck experienced visual , somatic and neurological symtoms of high pressure nervous syndrome (HPNS).The symptoms resolved during his ascent to his first deco stop at 400 ffw, this resolved and there was no persistent effects. Both divers on the tragic day of diving Zacaton used seperate descent lines, This was to remove any chance of making contact or possible interference, The descent in this kind of extreme diving would be rapid. Bowden would be using Heliair 6.4 and Exley was using Hekiair 6. Both divers carried an assortment of tables since the exact time of descent (Bottom Time" and maximum depth of the dive was unknown.

Going back to David Shaw, He dived Bushmans hole previously and hit the bottom safely, he decided to leave his shotline which is not recommended but he did and he found another tunnel. That is when he spotted Deon Dreyers body which lead to another dive. If he never left his shotline he would not of found Dreyer and might still be alive today. It is a sad fact but the human body can't take those kind's of pressures for very long, Exploring a new tunnel at 1000 feet is incredible but also very dangerous and it is very sad that David Shaw died under the circumstances. Maybe there is another tunnel at the bottom of Bushmans hole and Dreyers body was discovered there. A very dangerous scenario and cave system for sure. For every minute Shaw was at the bottom added another hour of decompression time so every second was extremely valuable.

David Shaw after his record-breaking descent into Bushman's Hole, when he first found Deon Dreyer's body.

Only two divers had ever been to this depth in Bushman's before. One of them, a South African named Nuno Gomes, had claimed a world record in 1996 when he hit bottom, on open-circuit gear, at 927 feet. Gomes had turned immediately for the surface. But Shaw, a Cathay Pacific Airways pilot based in Hong Kong and a man who had become one of the most audacious explorers in cave diving, didn't strive for depth alone. He planned to bottom out Bushman's Hole at a depth that no rebreather had ever been taken, connect a light reel of cave line to the shot line, and then swim off to perform the sublime act of having a look around.

Shaw felt remarkably relaxed, sweeping his light left and right, reveling in the fact that he was the first human ever to lay line at this depth. Suddenly, he stopped. About 50 feet to his left, perfectly illuminated in the gin-clear water, was a human body. It was on its back, the arms reaching toward the surface. Shaw knew immediately who it was: Deon Dreyer.
Shaw turned immediately, unspooling cave line as he went. Up close, he could see that Deon's tanks and dive harness, snugged around a black-and-tan wetsuit, appeared to be intact. Deon's head and hands, exposed to the water, were skeletonized, but his mask was eerily in place on the skull. Thinking he should try to bring Deon back to the surface, Shaw wrapped his arms around the corpse and tried to lift. It didn't move. Shaw knelt down and heaved again. Nothing. Deon's air tanks and the battery pack for his light appeared to be firmly embedded in the mud underneath him, and Shaw was starting to pant from exertion.

Nuno Gomes is a South African scuba diver of Portuguese descent, He was born in Lisbon, but his family relocated to Pretoria when he was 14 years old. He is the holder of two world records in deep diving (Independently verified and approved by Guinness World Records) the cave diving record from 1996 to the present and sea water record from 2005 to 2014.
Gomes used self-contained underwater breathing apparatus to dive to a depth of 318 metres (1,044 ft) in the sea. The dive was done in the Red Sea off the coast of Egypt near Dahab in June 2005. Gomes' total dive time was 12 hours and 20 minutes; the descent took only 14 minutes. He is one of only three men verified by Guinness World Records to have dived with scuba equipment (using trimix below 300 m (1,000 ft); the other two divers are the late John Bennett and Ahmed Gabr.
Gomes is also a renowned cave diver and holds the official current Guinness World Record for the deepest cave dive, done in Boesmansgat cave (South Africa)to a depth of 283 m (927 ft), in 1996. The cave is located at an altitude of more than 1,500 m (5,000 ft) above sea level, which resulted in Nuno having to follow a decompression schedule for an equivalent sea level dive depth of 339 m (1,112 ft) to prevent decrompression sickness. The total dive time was 12 hours and 15 minutes; the descent took 14 minutes with 4 minutes spent at the bottom.

This isn't wise, he chastised himself. I'm at 270 meters and working too hard. He was also already a minute over his planned bottom time. Shaw quickly tied the cave reel to Deon's tanks, so the body could be found again, and returned to the shot line to start his ascent."Dave felt very connected with Deon," Shirley says. "He had found him, so it was like a personal thing that he should bring him back."

Deon Dreyer (7 August 1974 – 17 December 1994) was a South African recreational scuba diver.
Dreyer's father, Theo (who owns a business that sells and services two-way radios) and mother, Marie, raised him in the town of Vereeniging, about 35 miles south of Johannesburg, Dreyer designed "obscenely loud car stereos", had a passion for diving, and loved adventure, (e.g., hunting, racing a souped-up car, and motorcycling).Deon had logged about 200 dives when he was invited to join some South Africa Cave Diving Association divers at Bushmans hole over the 1994 Christmas break. They planned a descent to 492 feet and asked Deon to dive support. He was thrilled. Two weeks before the expedition, Deon's grandfather passed away. Sitting around a barbecue with his family one night, Deon spoke with boyish hubris. "He said if he had a choice of how to go out in life, he'd like to go out diving," recalls his father, Theo, 51
Dreyer drowned on December 17, 1994, aged 20, during a practice dive while helping a team, assembled by Nuno Gomes, set up conditions for a deep, technical dive scheduled to take place later that week. According to first-hand accounts from those diving with him, Dreyer was lost on ascent around 50 metres (160 ft) from the surface. They conjectured he had probably lost consciousness either because of oxygen toxicity or hypercapnia induced by the high work rate of breathing at depth. (CO2 retention, is a condition of abnormally elevated carbon dioxide levels in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs. (Hypercapnia normally triggers a reflex which increases breathing and access to oxygen (O2) such as arousal turning the head during sleeping. A failure of this reflex can be fatal.) 

Two weeks after Dreyer's death, Theo hired a small, remotely operated sub used by the De Beers mining company, It found Dreyer's dive helmet on the Cenote floor, but there was no sign of the body.Dreyer's parents erected a plaque on a rock wall above the Bushman's Hole entry pool, in memory of their son. In Phillip Finch's book Diving Into Darkness: A True Story of Death and Survival, it was suggested that one of the reasons Dreyer's death created such an impression on the cave diving community was because of the plaque. The bodies of most other divers who die, even whilst cave diving, are recovered. However, for many years it was assumed Dreyer's body would never be recovered from the cave because it was simply too deep, but the plaque was a continual reminder to cave divers that his body lay within.

Documentary about great cave diver Dave Shaw. David Shaw was an Australian scuba diver, a technical diver and an airline pilot for Cathay Pacific, who flew the A330-300, A340-300 and A340-600. He is one of only nine people who have dived below a depth of 240 metres (800 ft) on self-contained underwater breathing apparatus.

Dreyer's parents erected a plaque on a rock wall above the Bushman's Hole entry pool, in memory of their son

Exley showed signs of an underlining medical condition once he was deep underwater at Bushmans hole, He had reached a depth of 863 feet and suffered from visual, somatic and neurological symptoms of (HPNS)HPNSS
A syndrome related to increased atmospheric pressure and characterized by tremors, nausea, dizziness, decreased motor and mental performance, and SEIZURES. This condition may occur in those who dive deeply (c. 1000 ft) usually while breathing a mixture of oxygen and helium. The condition is associated with a neuroexcitatory effect of helium. Maybe this was a warning but Exley ignored it, He may of suffered severe (HPNS) while deep down in Zacaton which proved to be fatal.