Cave Diving

Cave Diving

Cave diving is underwater diving in caves which are at least partially filled with water. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave diving is done using scuba equipment, often in specialized configurations. Cave diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves decompression.

In the United Kingdom it is an extension of the more common sport of caving, and in the United States an extension of the more common sport of scuba diving. Compared to caving and scuba diving, there are relatively few practitioners of cave diving. This is due in part to the specialized equipment (such as rebreather  diver propulsion vehicles and dry suits) and skill sets required, and in part because of the high potential risks, including decompression sickness and drowning.

Despite these risks, water-filled caves attract scuba divers, cavers, and speleologists due to their often unexplored nature, and present divers with a technical diving challenge. Underwater caves have a wide range of physical features, and can contain fauna not found elsewhere.

History

Jacques-Yves Cousteau, co-inventor of the first commercially successful open circuit scuba equipment, was the world's first scuba cave diver. However, many cave divers’ penetrated caves prior to the advent of scuba with surface supplied breathing apparatus through the use of umbilical hoses and compressors. Scuba diving in all its forms, including cave diving, has advanced in earnest since Cousteau introduced the Aqua-Lung in 1943.

There are three main classifications of diving: cave diving, open-water diving and cavern diving. Open-water diving is where all divers start gaining experience, and it's defined as a dive in which linear access to the surface is directly available -- in other words, by swimming straight up, a diver should be able to get a head above water, and sunlight is easily visible. In cavern diving, on the other hand, a diver is exploring permanent, naturally occurring caverns and has a ceiling overhead, but an entrance and visible light from the sun are in sight. Both open-water diving and cavern diving are considered recreational activities that require recreational-level certifications and training, and divers usually limit descents to 130 feet.

Cave diving differs from the other two types of diving in that it's a form of technical diving instead of a recreational one. It requires a much different set of equipment and several years of training and certification, and professionals constantly stress the need for top-notch fitness and gear. But above all, they admire cave diving for its unique challenge and the potential to discover the undiscovered -- scientific research gathered from cave dives can lead to the study of rare organisms and even offer cures to diseases like leukemia.

Cave Diving Techniques

Moving around the cave

Since cave diving is different from other recreational diving activities, many of the techniques people use are also much different. Divers are taught to swim in a prone, or face down, position, with the knees bent and the fins elevated above the plane of the body. This is mainly a precaution against kicking the bottom of a cave and stirring up sediment, but it also offers a good streamline and creates little resistance to the water.

Cave divers move about a cave by using a simple technique called "pull and glide" -- using the tips of their fingers, divers look for crevices in rock for a place to hook onto. The rock is usually something hard and porous like limestone, so it should have lots of pockets and places to grab. After grabbing hold, divers pull and release, gliding through the cave with relative ease.

Cave divers learn how to use mostly their feet for directional changes along with short flutter kicks, and, in the case of solid limestone, some can push off a cave ceiling with their feet to propel themselves along.

Divers can also take along battery-powered diver propulsion vehicles (DPVs) to make swimming easier. Although there are many different types, tow-behind DPVs are the most common, which pull divers through caves. DVPs help divers use less oxygen since they're not exerting themselves as much, and they can significantly increase the length of a dive.

Guidelines

Because there is little to no visibility in caves and cave divers must use their own source of light, guidelines must be placed to ensure people can find their way back to a cave's entrance.

Most caves already have guidelines in place from past explorers -- these are called "gold lines" because of their yellowish color. They consist of braided nylon string and are usually a bit smaller in diameter than regular rope at about an eighth of an inch. These are placed throughout the main tunnels of a cave. Labyrinthine caves also have smaller side tunnels, and these are provided with smaller, white lines. They don't contact the main line; instead, they usually end within 5 to 10 feet of the main line.

The main line of a cave does not extend to the exit -- this prevents open-water divers or untrained or uncertified people from viewing it as an invitation to enter the cave. Therefore, a main guideline typically starts 50 to 100 feet inside a cave.

Still, it's a cave diver's responsibility to run a temporary line, or entry line, along a reel from the outside of the cave in order to maintain a continuous guideline from open-water to the main line. This provides direct access to a cave's exit. To make an entry line, divers make an initial tie-off to something sturdy, like a big rock. A secondary tie-off is also made in case the first one comes loose. The diver must be able to swim along the line with his hand around it, making an "OK" sign, and with his eyes closed make his way out of the cave. The line shouldn't be run near obstructions in order to avoid snags and keep out of the way of other divers.

Dorf markers, or small, plastic directional arrows, can be tied to lines. These point toward exits, just in case a diver becomes disoriented. Clips, markers that resemble clothespins, are also used at points for notation reasons, including max penetration (the furthest point reached inside the cave) and points of interest for other divers.

The average cave dive will last in excess of one hour, but some can last for as long as 15 hours if the right equipment and gas supply is available. Divers generally use what's called the "rule of thirds" -- when one third of a diver's air supply is gone, he will stop the dive and begin moving toward the cave's entrance.

Cave diving venues

Grand Bahamas Island

The caves and caverns of Grand Bahamas contain an immense underwater cavern with a vast flooded labyrinth of caverns, caves and submerged tunnels that honeycomb the entire island of Grand Bahamas and the surrounding sea bed. The inland caves are not abundant with life, but do contain creatures living in the caves other than the migrating gray snappers. Residents of these caves include a type of blind cave fish and remipedia that don't pose any threat to cave divers.

The caves in the Bahamas were formed during the last ice age. With much of the Earth's water held in the form of glacial ice, the sea level fell hundreds of feet, leaving most of the Bahamas banks, which are now covered in water, high and dry. Rain falling on the most porous limestone slowly filtered down to sea level forming a lens where it contacted the denser salt water of the ocean permeating the spongy lime stone. The water at the interface was acidic enough to dissolve away the limestone and form the caves. Then, as more ice formed and the sea level dropped even further, the caves became dry and rainwater dripping through the ceiling over thousands of years created the incredible crystal forests of stalagmites which now decorate the caves. Finally, when the ice melted and the sea level rose, the caves were reclaimed by the sea.

Central and Northern Florida, U.S

The largest and most active cave diving community in the United States is in north-central Florida. The North Floridan Aquifer expels groundwater through numerous first-magnitude springs, each providing an entrance to the aquifer's labyrinthine cave system. These high-flow springs have resulted in Florida cave divers developing special techniques for exploring them, since some have such strong currents that it is impossible to swim against them.

The longest known underwater cave system in the USA, The system, near Tallahassee, Florida, has multiple interconnected sinks and springs spanning two counties (Leon & Wakulla). One main resurgence of the system, Wakulla Springs, is explored exclusively by a very successful and pioneering project called the Woodville Karst Plain Project (WKPP), although other individuals and groups like the US Deep Cave Diving Team, have explored portions of Wakulla Springs in the past.

One deep underwater cave in the USA is Weeki Wachee Spring. Due to its strong outflow, divers have had limited success penetrating this first magnitude spring until 2007, when drought conditions eased the out-flowing water allowing team divers from Karst Underwater Research to penetrate to depths of 400 ft (120 m) The current deepest known underwater cave in the USA is Phantom Springs Cave located in west Texas. Phantom Springs has been explored down to 462 feet in water filled cave passages. This makes it the deepest underwater cave in the USA as of 2013.

The Florida caves are formed from geologically young limestone with moderate porosity. The absence of speleothem decorations which can only form in air filled caves, indicates that the flooded Florida caves have a single genetic phase origin, having remained water filled even during past low sea levels. In plan form, the caves are relatively linear with a limited number of side passages allowing for most of the guidelines to be simple paths with few permanent tees. It is common practice for cave divers in Florida to join a main line with a secondary line using a jump reel when exploring side passages, in order to maintain a continuous guideline to the surface.

Yucatan Peninsula, Mexico

While there is great potential for cave diving in the continental karst throughout Mexico, the vast majority of cave diving in Mexico occurs in the Yucatán Peninsula. While there are thousands of deep pit cenotes throughout the Yucatán Peninsula including in the states of Yucatán and Campeche, the extensive sub-horizontal flooded cave networks for which the peninsula is known are essentially limited to a 10 km wide strip of the Caribbean coastline in the state of Quintana Roo extending south from Cancun to the Tulum Municipality and the Sian Ka'an Biosphere Reserve, although some short segments of underwater cave have been explored on the north-west coast (Yucatán State).

In the Yucatán Peninsula, any surface opening where groundwater can be reached is called cenote, which is a Spanish form of the Maya word d’zonot. The cave systems formed as normal caves underwater, but upper sections drained becoming air filled during past low sea levels. During this vadose, or air filled state, abundant speleothem deposits formed. The caves and the vadose speleothem were subsequently reflooded and became hydraulically reactivated as rising sea levels also raised the water table. These caves are therefore polygenetic, having experienced more than one cycle of formation below the water table. Polygenetic coastal cave systems with underwater speleothem are globally common, with notable examples being on the Balearic Islands (Mallorca, Menorca) of Spain, the islands of the Bahamas, Bermuda, Cuba, and many more.

As with all cave speleothems, the underwater speleothems in the Yucatán Peninsula are fragile. If a diver accidentally breaks off a stalactite from the ceiling or other speleothem formation, it will not reform as long as the cave is underwater so active cave conservation diving techniques are paramount.

In plan form, the Quintana Roo caves are extremely complex with anastomotic interconnected passages. When cave diving through the caves, the pathways then appear to have many offshoots and junctions, requiring careful navigation with permanent tees or the implementation of jumps in the guideline.

The beginning of the 1980s brought the first cave divers from the U.S. to the Yucatán Peninsula, Quintana Roo to explore cenotes such as , Naharon and Maya Blue, but also to central Mexico where Resurgence Rivers such as Rio Mante, and sinkholes such as Zacaton were documented.

In the Yucatán, the 1980s ended with the discoveries of the Dos Ojos and Nohoch Nah Chich cave systems which lead into a long ongoing competition of which exploration team had the longest underwater cave system in the world at the time, with both teams vying for first place.

The beginning of the 1990s led into the discovery of underwater caves such as Aereolito on the island of Cozumel, ultimately leading to the 5th biggest underwater cave in the world.

United Kingdom

UK requirements are generally that all people wishing to take up cave diving must be competent cavers before they start cave diving. This is primarily because most British cave dives are at the far end of dry caves. There are individuals that begin cave diving directly from the recreational diving, but they represent a minority in the UK, and represent only a few percent of the Cave Diving Group (CDG).

Australia

Australia has many spectacular water filled caves and sinkholes, but unlike the UK, most Australian cave divers come from a general ocean-diving background.

The "air-clear" water conditions experienced in the sinkholes and caves found in the Lower South East (now called the Limestone Coast) of South Australia (SA) has attracted many visiting divers with the first cave and sinkhole dives taking place in the very late 1950s. Until the mid-1980s divers generally used single diving cylinders and homemade torches, and reels, resulting in most of their explorations being limited. Mixed-gas and rebreather technologies can now be used in many sites. The area is usually known within the cave diving community as the Mount Gambier region.

A series of incidents between 1969 and 1974 in the former Lower South East of SA in which 11 divers died (including a triple and a quadruple fatality) in the following four karst features - Kilsbys Hole, Piccaninnie Ponds, Death Cave (also known as Alleyns Cave) and The Shaft - created much public comment and led to the formation of the Cave Divers Association of Australia Inc. (CDAA) in September 1973. The introduction of a testing program by the CDAA in 1974, which involved the assessment of prospective cave divers' cave diving ability lead to a reduced fatality rate. In 1989, this testing system was replaced by a training system which currently consists of 3 levels of qualification - Deep Cavern, Cave and Advanced Cave. Five further deaths have occurred since 1974; two died at Piccaninnie Ponds in 1984, one person died at Kilsbys Hole in 2010, and two people died in separate incidents at Tank Cave in 2011 including noted cave diver Agnes Milowka.

During the 1980s, the Nullarbor Plain was recognized as a major cave-diving area, with one cave, Cocklebiddy, being explored for more than 6 kilometers, involving the use of large sleds to which were attached numerous diving cylinders and other paraphernalia, and which were then laboriously pushed through the cave by the divers. In more recent years divers have been utilizing compact diver-towing powered scooters, but the dive is still technically extremely challenging.

A number of other very significant caves have also been discovered during the past 20 years or so; the 10+ (Lineal) kilometer long Tank Cave near Millicent in the Limestone Coast, other very large features on the Nullarbor and the adjacent Roe Plain as well as a number of specific sites elsewhere, and nowadays the cave diving community utilizes many techniques, equipment and standards from the U.S. and elsewhere.

The CDAA is the major cave diving organization in Australia and is responsible for the administration of cave diving at many sites. All cave diving in the Limestone Coast as well as at some New South Wales sites and the Nullarbor requires divers to be members of the CDAA, whether in the capacity of a visitor or a trained and assessed member. A number of other organizations participate in cave diving activities within Australia. The Australian Speleological Federation Cave Diving Group which was formed in 2005 coordinates projects focused on exploration and mapping at sites throughout Australia. The following diving training organizations offer courses in various aspects of cave diving via instructors either resident in Australia or visiting from overseas - Global Underwater Explorers, International Association of Nitrox and Technical Divers and Technical Diving International.

Brazil

In Brazil there is cavern diving in Chapada da Diamantina, in Bahia state; Bonito, in Mato Grosso do Sul state; and Mariana, where there is also cave diving (visiting Mina da Passagem), in Minas Gerais state. For cave diving in Mariana a cave diver certification will be required.

Sardinia Italy

In the north west of Sardinia, close to Porto Conte bay, Alghero territory, there is the most important cave diving site in the Mediterranean Sea. Thanks to the huge limestone cliffs of Capo Caccia and Punta Giglio there are more than 300 caves above and below water, with about 30 large, and many smaller, underwater sea caves. The Nereo Cave is the most important and it is considered also the largest in the Mediterranean Sea. On the east side of Sardinia there are many underwater cave systems starting from the Gennargentu Mountains, with underwater rivers which arrive at the sea by different, lengthy routes. Here one of the deepest fresh water caves exits at more than 110 m (360 ft) depth.

Cala Golone is a departure point for cave diving in Sardinia's largest cave systems which are usually reached by sea. Bue Marino is the longest known, and there are several others with various lengths and depths.

West Timor, Indonesia

There are a number of freshwater filled cave sites located near and within Kupang, the principal city in West Timor and the provincial capital of East Nusa Tenggara. At least 2 sites have been described: Gua Oehani (translates as the Oehani Cave) and Gua Kristal (translates as the Crystal Cave).

As of 1999, there was no requirement to hold cave diving certification to dive either of these sites. However, competence equivalent to CDAA Advanced Cave and Cave/Advanced Cave appears to be respectively appropriate for these sites.

Dominican Republic

There is a growing number of known water filled caves in the Dominican Republic, spread all over the island. Regions with underwater caves include Santo Domingo, Pedernales, Cabrera, Bayahibe and others.

Active exploration is being conducted by the Dominican Republic Speleological Society which is working together with local institutions as well as international scientists to further explore all the cave systems possibilities and focusing in the preservation.

The longest known cave in the island is El Toro which is about6, 000 ft (1,800 m) in length.

The best known caves in the island are Cueva Taina, El Tildo, El Chicho and El Dudu, which have easy access to the water and with a good level of safety outside of the water as they are in private properties or national parks.

Cave diving is playing a very important role in science in the DR, {in the last 3 years the DRSS team together with international scientists and "Museo del Hombre Dominicano" has found a new species of cave bacteria, a number of new and extinct bat species, the first evidence of extinct crocodiles in the DR, fossil snakes, birds, sloths and remains of long extinct monkeys and other ancient cave life. DRSS has cataloged over 120 new springs all over the island in which many have caverns and cave systems attached.

Cave Diving Equipment

The best way to tell a cave diver apart from an open-water diver or cavern diver is to look at the equipment in use. In this section we'll look at the different kinds of gear a cave diver brings on a dive.

It's important to remember that cave divers carry redundant equipment -- this means that for every piece of equipment they carry, an extra will come along for the dive. This is to make sure that if something undergoes failure, there's a replacement to take over and allow a safe return to the surface. It could be something seemingly unimportant like an extra mask, or a piece of equipment that ensures a diver's survival, like an oxygen tank.

1.    Masks

While open-water divers usually use snorkels because they can easily reach the surface for air, cave divers could never afford to bring one along and have no use for it. Cave divers stay submerged in the water for long periods of time, and therefore bring along oxygen tanks for breathing purposes -- a snorkel would only create excess weight and extra drag.

Cave divers usually keep masks simple, preferring standard masks that are solid black. The reason dark masks are well suited for cave diving is because of the light-absorbing qualities of the color black. Any distracting light that might leak into the mask can be absorbed by the dark material of the mask and prevent a diver from losing sight of entrances or important spots. Cave divers also wear hoods made of nylon to protect their heads from water leaks and damage during dives.

2.    Fins

     Cave divers typically prefer black rubber fins, and ones that aren't very flexible. Light, stiff fins work best because divers already so carry much mass with them into a cave. Moving through the water, they need to use short, controlled kicks to avoid stirring up any sediment on the floor of a cave.

Stiff fins help cave divers move through the water easier, while dry suits keep them warmer. 


3.    Suits 

Cave divers use either dry suits or wet suits for protection. The difference between the two kinds of suits is that dry suits are designed to seal off water from entering and getting a diver's body wet. Made of a synthetic rubber called neoprene, dry suits are the preferred choice for cave divers because they allow much less heat loss. The material is double-layered with a small space in between for insulating air, and divers have the option of wearing extra undergarments. Wet suits will still suffice for shorter dives and warmer waters, however.

Other equipment such as flashlights and small knives to cut away snags come along on a dive. There are also several gadgets that help divers during their ascent and descent. Different gauges give information on air pressure and depth, and they may all be fitted onto one device along with a compass for navigation.

Cave divers, of course, need to bring oxygen tanks, or cylinders, with them while underwater. To learn about breathing in deep, high-pressure water, read the next page.

4.    Depth gauge and timer

Every diver carries at least one depth gauge and timer. These allow the diver to calculate what decompression stops to make when ascending at the end of the dive, using standard decompression tables. Alternatively, all of these functions may be combined in a dive computer which indicates depth, time and the required decompression stops.

5.    Tanks, Back plate & Harness

The heart of a cave diver's equipment is the "doubles". These are two tanks held securely together by steel bands, and connected together by a manifold. The manifold has two outlets, each of which can be turned on or off independently in case of problems. The center knob allows the two tanks to be isolated if a problem cannot be solved by turning off one outlet.           

Two fully independent air regulator systems are attached to the outlets of the manifold.  Each regulator system has a "first stage", which reduces the pressure from approximately 200 atmospheres to about 10 atmospheres, and a "second stage" (the mouthpiece) which supplies air on demand at ambient pressure.  A long hose on one regulator allows divers to share air if necessary while swimming in line through narrow caves.

A buoyancy compensation device, or "wing", is attached to the tanks. This is essentially an airtight bag which can be inflated to provide buoyancy. Valves allow air to be injected from the tanks or from the diver's mouth to increase buoyancy, or to be released to reduce buoyancy.

Valves allow air to be injected from the tanks or from the diver's mouth to increase buoyancy, or to be released to reduce buoyancy.

The back plate and harness bolt onto the doubles and holds the wing in position.

The harness is made from nylon webbing threaded through the back plate and holds the equipment firmly in place on the diver.

6.    Safety Equipment

     Each diver carries a powerful primary light. The canister contains a lead-acid "gel cell" of 6.5 AH (shown left), 9AH or 14 AH capacity and is worn on the harness. The light head is a 10W High Intensity Discharge unit and is connected via a wet connector which can be plugged and unplugged under water.

       Primary lights fail fairly frequently, perhaps every 50 to 100 dives.  Each diver, therefore, also carries two backup lights.  These are extremely reliable, and provide sufficient light to exit the cave if all primary lights fail.  The backup lights are clipped onto D-rings on the diver's harness.    

        Also attached to the harness is a short, sharp knife.  This allows the diver to cut himself free in the event of entanglement in the guideline or other equipment.  It is common for cave divers to carry more than one knife--we normally attach another knife to the handle of the light head.
 

    Cave divers place directional markers (arrows) and non-directional markers (circles) on the guideline to record information.  Directional markers point to the nearest exit from the cave, and non-directional markers are used for a number of purposes, including marking the entrance route. 


Each diver always carries a small reel or spool of nylon line known as a "safety reel".  This is used when conducting a search for a lost guideline or fellow diver, and to repair any breaks in the guideline.

 
         Waterproof notebooks, or "Wet Notes" are used for a number of purposes.  One use is for communication under water, and another is to record reference information during the dive, either to help with navigation inside the cave or for later analysis and planning of subsequent dives.

7.    Breathing Gasses

Air was the first gas used for scuba diving. It consists of about 21% oxygen and 79% nitrogen. The high nitrogen component limits the use of air. The reason is that the nitrogen is absorbed by the body tissues while diving, and can cause bubbles to form when the diver surfaces. In addition, the nitrogen acts as a narcotic at depths below about 30 meters, affecting the diver's judgment and performance.

For most of our dives we, therefore, use a gas mixture known as Nitrox 32%.  This contains 32% oxygen and only 68% nitrogen.  The lower nitrogen content reduces the amount of nitrogen which is absorbed by the body, reducing the risk of bubble formation.  The mixture is still narcotic under pressure, and the high oxygen content can be toxic at depth.  This limits the safe use of Nitrox 32% to depths of about 30 meters.

To help eliminate any bubbles during ascent, we make a number of decompression stops at different depths during the ascent.  For the final stop at six meters, we breathe pure oxygen which rapidly eliminates bubbles.  Risks of oxygen toxicity limit the use of pure oxygen to a depth of six meters.

For dives deeper than 30 meters, the narcotic effect of the nitrogen can be avoided by replacing it with another inert gas:  helium.  A typical mixture for depths up to 60 meters would be "20/50" - this consists of 20% oxygen, 50% helium, and 30% nitrogen.  Mixtures of oxygen, helium and nitrogen are called Trimix.

Dives below 60 meters require special considerations.  The amount of nitrogen must be reduced to a very low level in order to avoid narcosis.  To prevent oxygen toxicity the amount of oxygen must be reduced as well.  A typical mixture for dives up to 120 meters would be 10/70, containing 10% oxygen, 70% helium and 20% nitrogen.  Breathing such a mixture at shallow depths would result in insufficient oxygen supply for the body and must be avoided.

8.    Stage Tanks

When the breathing gas requirement exceeds the capacity of the doubles, extra gas can be carried in so-called stage tanks. Stage tanks are fitted with clips to fasten the tank to the diver's harness. Stage tanks can also be left clipped to the guideline - this is common on very long dives, to provide an additional safety margin during the exit.

Stage tanks are also used when different gas mixtures must be carried, most commonly for oxygen. When diving with several gases, it is important that no gas is taken deeper than its maximum safe operating depth.

Each stage tank has a regulator system attached, consisting of one first stage, one second stage, and a pressure gauge to show the tank contents. When not in use, the second stage and hoses are secured neatly in rubber tubes around the tank.

9.    Diver Propulsion Vehicles (DPVs)

    Normal swimming speed for a cave diver is 15-20 meters per minute. We use diver propulsion vehicles (DPVs or "scooters") when large distances must be covered, or when lots of equipment must be carried. These are capable of pulling a fully equipped cave diver with several stage tanks at speeds of 50-60 meters per minute. The small scooters have a range of about three kilometers, and the larger scooters have a range of about six kilometers. The scooters are powered by several large lead-acid get cells housed in the tubes.

The photo to the right shows an exploration diver with a scooter and one stage tank.  This equipment configuration is suitable for cave penetrations of up to about two kilometers.  For longer penetrations we take two or three stage tanks and tow a second scooter behind us.  This allows penetrations of up to about five kilometers.  Whenever we use scooters, we allow sufficient reserve breathing gas to swim out from the furthest point if all scooters fail.