Indian Springs- photo courtesy of Cave Connections Dive Shop
In November of 1991 news of the tragic death of well known cave explorer Parker Turner shook the cave diving community to its core. Turner and exploration partner Bill Gavin were conducting a well planned deep exploration dive at Indian Springs in Wakulla County, Florida when the unthinkable happened. A sudden collapse and flow reversal near the entrance to the cave trapped the team underwater in the cave system and only Gavin managed to escape with his life.
For over twenty years the exact cause has remained a mystery and the chilling reality of a collapse claiming the life of one of cave diving’s best has led to speculation, conjecture, and a large amount of introspection. Now, after years of work, one experienced cave diver has provided scientific evidence to support his theory about the cause of this tragic and shocking event.
Professor Doron Nof
Cave diver Doron Nof, Ph.D. – Distinguished Nansen Professor of Physical Oceanography at Florida State University, has published a paper in the prestigious journal PLOS One documenting scientific experiments Nof believes proves his theory that SCUBA divers’ exhaled gases during decompression stops led to the collapse that claimed the life of 39 year old Parker Turner at Indian Springs.
Indian Springs is on private property owned by Camp Indian Springs, a recreational camp in northwest Florida. It is part of the larger underwater cave system that connects to famous Wakulla Springs and the Floridan Aquifer. Here, miles of cave passages have been explored and records have been set by the cave exploration organization known as WKPP- Woodsville Karst Plain Project, of which Turner was a founder. Depths at Indian Springs are greater than normal recreational diver limits of 130 feet. Diving there requires experience, specialized training, and Trimix breathing gases with a custom mix of Oxygen, Nitrogen, and Helium. Today the spring is open to cave divers who are properly trained, experienced, and equipped. All divers must be accompanied by a qualified guide.
On November 17, 1991 a group of cave exploration divers from the WKPP met at Indian Springs to conduct a research dive that had been in planning for nearly two years. The goal was to locate new passages in the deeper section of the cave. Parker Turner and Bill Gavin were prepared and equipped for the deep dive requiring specialized mixed breathing gases and long decompression. Other experienced members of the group acted as support divers and were in the shallower sections of the cave testing new equipment. The two exploration divers successfully completed their planned dive which included a transit of 40 minutes at 140 feet depth and a 20-25 minute search for unexplored passage at a depth of 300 feet. They were returning to the entrance to complete their decompression when something went terribly wrong.
As the divers ascended and moved closer to the exit they encountered billowing clouds of silt completely obscuring visibility. Following the guideline that would take them to safety they discovered it was buried under sand and debris. The exit to the cave system had been blocked by a collapse of sand, mud, and rock.
As other team divers decompressed near the cave entrance limestone rocks suddenly became dislodged from the cave ceiling and fell to a sloping bank of rocks, sand, and mud below. This caused an underwater landslide with the muddy debris sliding further into the cave. The cave was now almost completely blocked and the normally clear water was so muddied that visibility was near zero. The surface support team reported a rapid drop in the water level of the sink, a temporary reversal of the flow, then a return to normal levels when the collapse occurred.
The two experienced cave divers trapped by this freak accident acted to assess the situation and took action by managing their gas supply and searching for an exit but sadly, only one diver in the team survived. Read Bill Gavin’s account here.
Since the accident there has been considerable speculation about the cause. There were accusations that a diver testing a new diver propulsion vehicle or “scooter” had impacted the cave, causing the collapse. Some felt that land clearing or blasting with explosives nearby were the cause. Others felt that bubbles exhaled during SCUBA divers’ decompression may have been the cause but no scientific support has been offered until now.
Doron Nof is a scientist and long time SCUBA diver who has been interested in the Indian Springs accident for years. I asked him how long he’s been SCUBA diving and he responded with a chuckle and said “Forever, 45- 50 years.” He became a cave diver 11 years ago but has been aware of the accident since 1991. He said, “I’ve been thinking about it since it happened. It didn’t make much sense so I was curious.” He said there were various opinions about the case, “that didn’t add up.” So he set out to do his own research and formulated a theory about the cause of the Indian Springs collapse. Nof believes that the collapse was caused by exhaled breathing gases from the SCUBA divers in the cave and published an article in 2009 supporting his theory. Now he has published a paper detailing experiments that demonstrate the physics that led to the tragedy at Indian Springs.
The culprit was indeed bubbles exhaled during decompression. Routinely, cave dives are decompression dives requiring SCUBA divers to make planned extended stops as they ascend. Long deep dives at Indian Springs require extensive decompression and the longest stops are typically in the 10 to 20 feet depth range. When a diver is decompressing for 30 minutes or more in one place in the small cave passage a considerable amount of gas is exhaled and trapped at the top of the cave. Bubbles change the density of the water and reduce the buoyancy, which affects the stability of the limestone and dolomite making up the cave ceiling and walls. With several divers in the cave on that fateful November day the buildup of exhaled gas changed the buoyancy near the opening, causing the rocks in the ceiling to effectively weigh more. They dislodged from the ceiling and crashed to the unstable floor below; creating the landslide that was to claim the life of Parker Turner.
The Indian Springs incident was caused by a unique set of circ*mstances not often encountered in cave diving. In Doron Nof’s words, “There were three processes that contributed to the Indian Spring collapse, all of which were necessary for the blockage to occur. First, someone was decompressing for a long time in the same spot, releasing large number of bubbles to the cracks in the ceiling directly above him. Second, the bottom of the cave below the decompressing diver consisted of sediment, whose slope was fairly close to what is normally called “critical slope” (in dry slope dynamics). Third, there was a restriction upstream of the sloping sediment. As mentioned, all three components had to be present for the accident to occur. The bubbles expelled by the decompressing diver released rocks from the top. These rocks fell on the unstable slope and caused a mudslide similar to that that occurs on dry land due to heavy rains. The mudslide moved down hill blocking the restriction.”
Image courtesy of Doron Nof -Laboratory experiment for bubble-induced cave collapse (with a convex ceiling).
Now, the apparatus is a cylindrical chamber (radius and width are 6.4 cm and 3.3 cm, respectively) with a convex ceiling. It is again filled with water (colored). The chamber is equivalent to a cave with a circular cross section. Air bubbles are again released at the bottom of the chamber using a syringe. The tube on the left side of the chamber removes water displaced by the bubbles. In this demonstration, the bubbles cause a flow past the metal ball and accumulate away from the metal ball, due to the convex shape of the cave ceiling. (a) Experimental set up before bubble release. (b) Bubbles released at the bottom using a syringe. (c) Point at which the metal ball loses its buoyancy due to the bubbles. (d) The ball falling to the bottom of the chamber, due to gravity.
To prove his theory Nof and two researchers, graduate student Lakshika Girihagama and Cathrine Hanco*ck, a researcher with the Geophysical Fluid Dynamics Institute set up an experiment that would test buoyancy effects on suspended material.
With the help of FSU’s Geophysical Fluid Dynamics Institute a circular glass structure to simulate the interior of a cave was created and filled with an orange liquid. At the top of the structure the team attached a strong magnet. A metal ball was held in place at the top by the magnetic field to simulate a rock in the cave ceiling.
Nof and his team pushed air through a line into the bottom of the glass structure creating bubbles like a SCUBA diver. As the bubbles began moving to the top the ball began to wobble. After a few seconds it became completely dislodged from the magnetic force and fell to the bottom of the glass, illustrating how material in the cave ceiling could have done the same. “Because of the bubbles, the buoyancy is reduced,” Nof said. “So, the object weighs more.”
This experiment conclusively proves the theory that the collapse at Indian Springs was caused by bubbles from divers but it has far reaching implications for cave divers everywhere. I asked Doron Nof if he thinks about the possibility of a collapse when he is cave diving and if he has any recommendations for cave divers. He said, “I have actually thought a great deal about your question during the past few years. No easy answers, unfortunately. Of course, using re-breathers will avoid the bubbles issue altogether but it brings in other risks which might be greater than that which we are trying to avoid. My recommendation–avoid decompression in the same place if you suspect that the ceiling above you contains some rocks which may fall down due to bubbles.”
CLICK HERE TO READ THE ENTIRE ARTICLE FROM PLOS ONE
