A 'bottomless' pit of water in Australia claimed the lives of four divers who became lost in its tunnels.
In 1938, a farmer near Mount Gambier, South Australia, came across a sinkhole after his horse tripped over in a field. Although he tried to fill the hole with rocks, became clear pretty soon that it was much deeper than he could 'even test.'
News spread of the mysterious shaft, drawing in adventurous divers who travelled from far and wide to see what all the fuss was about.
For years, divers explored The Shaft without incident - until 1973.
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On 28 May 1973, eight divers entered the depths with only four making it back to the surface, according to CaveDivers.com.au.
The main chamber spans 140 metres across and 80 metres wide at its narrowest, with two large tunnels branching off beneath a rock pile at 36 metres underwater, Borderwatch reports.
"There was no hope of recovering alive any of the overdue divers from the outset," former Chief Superintendent Wallace B. Budd later wrote.
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"Almost eight months elapsed before the first body was located and that was only by chance."
He added: "The remaining victims stayed hidden in the cold, perilous depths of 'The Shaft' until two members of the squad were trained in deep diving techniques by Royal Australian Navy instructors." But, the process took months due to the extreme conditions.
Over the course of separate dives, the bodies of siblings Stephen Millott (22) and Christine M. Millott (19) were found, along with Gordon G Roberts (28) and John H. Bockerman.
One of the survivors, Glen Millott (25) - Stephen and Christine’s brother - tried desperately to find them but was forced to surface when his oxygen ran low.
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Before the accident, The Shaft had been considered one of the world’s 'most spectacular diving caves,' with an estimated 8,000 dives having taken place, as per CaveDivers.com.au.
Survivors recalled that everything went wrong for the four fatalities when their movements kicked up a dense cloud of silt, blocking their vision and leaving them stranded. One survivor, Robert Smith (then 26), explained that he left the group after feeling the symptoms of nitrogen narcosis - the result of nitrogen entering the blood at depths greater than 120 feet.
"I immediately went to where I had last seen the others and in fact, I went to 200 feet towards the 'drop off', and just before the 'drop off' I found Stephen Millott's torch and camera," Smith described.
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"I went on and noticed that the bottom had become silted up very badly. I went over the 'drop off' to 225 feet. I could not see a hand in front of me. I could not see anybody."
Budd reflected on the lives lost in the tragedy and the sobering fact that they may not be the last.
"Sadly theirs is the old story of high adventure gone wrong," he wrote. "So long as the human race endures and walks hand-in-hand with the Goddess Curiosity, the story will have many sequels."