Cave diving

Most open-water diving skills apply to cave diving, and there are additional skills specific to the environment, and to the chosen equipment configuration.

• Good buoyancy control, trim and finning technique help preserve visibility in areas with silt deposits.
• The ability to navigate in total darkness using the guideline to find the way out is a safety critical emergency skill. Line management skills required for cave diving include laying and recovering guide lines using a reel, tie-offs, the use of a jump line to cross gaps or find a lost guide line in silted out conditions, identifying the direction along the guideline leading to the exit, and the skills of dealing with a break in a guideline.[2][3]
• Emergency skills for dealing with gas supply problems are complicated by the possibility of the emergency occurring in a confined space and low visibility or darkness.

The essential cave diving procedure is navigation using a guide line. This includes laying and marking line, following line and interpreting line markers, maintaining and repairing line, finding lost line, jumping gaps, and recovering line, any of which may need to be done in zero visibility, total darkness, tight confined spaces or a combination of these conditions.

• Laying a cave line
  • Temporary line
  • Permanent line
• Marking line
  • Directional markers
  • Personal markers
• Following a line
• Finding a lost line
• Fixing a line break
• Jumping a gap to a branch line
• Recovering temporary line

Cave diving training includes equipment selection and configuration, guideline protocols and techniques, gas management protocols, communication techniques, propulsion techniques, emergency management protocols, and psychological education. Cave diver training also stresses the importance of risk management and cave conservation ethics. Most training systems offer progressive stages of education and certification.

• Cavern training covers the basic skills needed to enter the overhead environment. Training will generally consist of gas planning, propulsion techniques needed to deal with the silty environments in many caves, reel and handling, and communication. Once certified as a cavern diver, a diver may undertake cavern diving with a cavern or cave certified "buddy", as well as continue into cave diving training.[4]
• Introduction into cave training builds on the techniques learned during cavern training and includes the training needed to penetrate beyond the cavern zone and working with permanent guidelines that exist in many caves. Once intro to cave certified, a diver may penetrate much further into a cave, usually limited by 1/3 of a single cylinder, or in the case of a basic cave certification, 1/6 of double cylinders. An intro cave diver is usually not certified to do complex navigation.[4]
• Apprentice cave training serves as the transition from intro to full certification and includes the training needed to penetrate deep into caves working from permanent guide lines as well as limited exposure to side lines that exist in many caves. Training covers complex dive planning and decompression procedures used for longer dives. Once apprentice certified, a diver may penetrate much further into a cave, usually limited by 1/3 of double cylinders. An apprentice diver is also allowed to do a single jump or gap (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive. An apprentice diver typically has one year to finish full cave or must repeat the apprentice stage.[4]
• Full cave training serves as the final level of basic training and includes the training needed to penetrate deep into the cave working from both permanent guidelines and sidelines, and may plan and complete complex dives deep into a system using decompression to stay longer. Once cave certified, a diver may penetrate much further into a cave, usually limited by 1/3 of double cylinders. A cave diver is also certified as competent to do multiple jumps or gaps (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive.[4]

Cave diving equipment from 1935 in the museum at Wookey Hole Caves

The Cave Diving Group (CDG) was established informally in the United Kingdom in 1935 to organise training and equipment for the exploration of flooded caves in the Mendip Hills of Somerset. The first dive was made by Jack Sheppard on 4 October 1936,[14] using a home-made drysuit surface fed from a modified bicycle pump, which allowed Sheppard to pass Sump 1 of Swildon's Hole. Swildon's is an upstream feeder to the Wookey Hole resurgence system. The difficulty of access to the sump in Swildon's prompted operations to move to the resurgence, and the larger cave there allowed use of standard diving dress which was secured from the Siebe Gorman company. In UK cave diving, the term "Sherpa" is used without a drop of irony for the people who carry the diver's gear although this has gone out of fashion; support is now more normally used, and before the development of SCUBA equipment such undertakings could be monumental operations.

Diving in the spacious third chamber of Wookey Hole led to a rapid series of advances, each of which was dignified by being given a successive number, until an air surface was reached at what is now known as "Chamber 9." Some of these dives were broadcast live on BBC radio, which must have been a quite surreal experience for both diver and audience.

Cave diving equipment in the museum at Wookey Hole Caves

The number of sites where standard diving dress could be used is clearly limited and there was little further progress before the outbreak of World War II reduced the caving community considerably. However, the rapid development of underwater warfare through the war made a lot of surplus equipment available. The CDG re-formed in 1946 and progress was rapid. Typical equipment at this time was a frogman rubber diving suit for insulation (water temperature in the UK is typically 4 °C), an oxygen diving cylinder, soda lime absorbent canister and counter-lung comprising a rebreather air system and an "AFLOLAUN", meaning "Apparatus For Laying Out Line And Underwater Navigation." The AFLOLAUN consisted of lights, line-reel, compass, notebook (for the survey), batteries, and more.

Progress was typically by "bottom walking", as this was considered less dangerous than swimming (note the absence of buoyancy controls). The use of oxygen put a depth limit on the dive, which was considerably compensated by the extended dive duration. This was the normal diving equipment and methods until approximately 1960 when new techniques using wetsuits (which provide both insulation and buoyancy ), twin open-circuit SCUBA air systems the development of side mounting cylinders, helmet-mounted lights and free-swimming with fins. The increasing capacity and pressure rating of air bottles also extended dive durations.[15]

In the 1970s, cave diving greatly increased in popularity among divers in the United States. However, there were very few experienced cave divers and almost no formal classes to handle the surge in interest. The result was a large number of divers trying to cave dive without any formal training. This resulted in more than 100 fatalities over the course of the decade. The state of Florida came close to banning SCUBA diving around the cave entrances. The cave diving organizations responded to the problem by creating training programs and certifying instructors, in addition to other measures to try to prevent these fatalities. This included posting signs, adding no-lights rules, and other enforcements.

In the United States, Sheck Exley was a pioneering cave diver who first explored many underwater cave systems in Florida, and many throughout the US and the world. On 6 February 1974, Exley became the first chairman of the Cave Diving Section of the National Speleological Society.[16]

Since the 1980s, cave diving education has greatly reduced diver fatalities, and it is now rare for an agency trained diver to perish in an underwater cave. Also in the 1980s, refinements were made to the equipment used for cave diving, most importantly better lights with smaller batteries. In the 1990s, cave diving equipment configurations became more standardized, due mostly to the adaptation and popularization of the "Hogarthian Rig", developed by several North Florida cave divers, named in honor of William "Hogarth" Main, which promotes equipment choices that "keep it simple and streamlined".

Today, the cave community is most focused on training, exploration, public awareness, and cave conservation.

Documentary films made by Wesley C. Skiles and Jill Heinerth have contributed to the increasing popularity of cave diving in the early 21st century.

• Anjanamba is Africa's longest flooded cave, exceeding over 10 kilometers of passages.[17]

• Boesmansgat is a sinkhole in the Northern Cape province has been dived to 282.6 metres depth.
• Wondergat (more of a cavern, but with a small cave section)
• Komati Springs – a flooded mine

• Chinhoyi Caves

The Karst landforms in China's Guangxi, Yunnan, Guizhou and other provinces are extremely conducive to the development of caves, and thus give rise to rich groundwater features. 10 underground rivers with a length of more than 80 kilometers have been discovered, with hundreds of caves, skylights, "Feilai Lake" and other landscapes. However, in Guangxi and other places, the caves available for diving also have the characteristics of large water flow, fast speed, deep caverns, complex structure, and harsher cavern environment.

In recent years, Nanning Red Army hole, the sun and the moon hole, Liuzhou Fairy Cave, a series of cave systems attracts a large number of cave diving enthusiasts.[18]

Pawod Underwater Cave in Mactan Island, off the island of Cebu in the Central Philippines was discovered in 2001 by Dr. Alfonso Amores. The discovery opened cave diving for the locals who erstwhile could not afford the expensive course in Florida. In 2012, Jake Miranda, Dr. Alfonso Amores and Bernil H. Gastardo founded the Filipino Cave Divers (FCD).[19] Exploration opened the freshwater caves of Casili, Balamban in Cebu Island and Enchanted River Underwater Cave in Hinatuan, Surigao del Sur in the big southern island of Mindanao. Several more caves in Mindanao have since been discovered and explored – Bababu Lake (Dinagat Island), Pamutuanan Cave (Lianga, Surigao del Sur) and Campomento Cave (Lanuza, Surigao del Sur).

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).[20][21]

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 respectively appears to be appropriate for these sites.[22]

Diving in Piccaninnie Ponds

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.[23] 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.[24] The introduction of a testing program by the CDAA in 1974, which involved the assessment of prospective cave divers' cave diving ability led to a reduced fatality rate. In 1989, this testing system was replaced by a training system which consists of three levels of qualification – Deep Cavern, Cave and Advanced Cave.[25] 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.[26][27][28][29]

During the 1980s, the Nullarbor Plain was recognized as a major cave-diving area, with one cave, Cocklebiddy, being explored for more than 6 kilometres, 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) kilometre 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 common internationally.

The CDAA is the major cave diving organisation 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 organisations 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.[30] The following diving training organisations 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.

Una National Park, in the Bihac municipality, encompasses the valley of the Una River and is a hotspot for speleological research expeditions. Thanks to the area's position between the end of two large karst systems: Plješivica and Grmeč, the river abounds with shallow water sources and a significant number of underwater caves.[31] So far, 10 large caves have been registered, only five of which have been partially examined.[32] Divers who have explored Klokot Spring have managed to reach a depth of 104.5 metres (343 feet; 57 fathoms), though the bottom of the spring has yet to be touched. Another cave has been explored to the length of 150 m (490 ft), and is said to be an ideal destination for cave divers in training.

Hranice Abyss, or Hranická Propast, is the world's deepest known underwater cavity. It beat the previous record holder, Pozzo del Merro in Italy, by 12 m (39 ft).[33] Polish explorer Krzysztof Starnawski, who has explored the upper parts of the flooded fissure for decades, has determined the depth to be at least 404 m (1,325 ft) . As of 2017, divers have yet to reach the bottom of the cave.[34]

Molnár János Cave is an active thermal water cave located on the western banks of the Danube river. Belonging to the Buda Hills karst system, which is home to many of Budapest's famed hot springs, the temperature of the water sits between 20–28 °C (68–82 °F) year-round.[35] Whilst the first underwater explorations began in the 1950s, the cave wasn't successfully chartered until the 70s and 80s when a group of divers mapped out more than 400 m (1,300 ft) of the cave system.[36] The cave, which contains a labyrinth passages, currently stretches to over 6 km (4 mi; 20,000 ft) though there are many more untouched sections to explore.

After the death of a diver in 2011, the Hungarian government imposed strict rules for diving. To dive at Molnár János, divers must have at least an intro-to-cave-diving certification or they cannot dive in the tunnels; they must have dive insurance that covers cave diving; and they must have air supplied in the form of double tanks, stages or a rebreather. In addition, each dive is accompanied by a guide, to minimize the risk of a wrong turn.[37]

Silfra is a fissure between the North American and Eurasian tectonic plates in Thingvellir National Park. It is the only place in the world where you can dive or snorkel directly in a crack between two tectonic plates.[38] The tunnel from the entrance of Silfra to the cave is commonly known as ‘The Tunnel’, due to the strong current that ‘flushes’ divers attempting to swim through. This tunnel is rarely dived due to the dangerous head-first vertical dive needed to pass through. The deepest part of the cave is at least 63 m (207 ft) deep, and has only been dived by a few people because of the narrow and unstable passages.[39]

The Nereo Cave "Belvedere" watching terrace, south upside entrance

Bue Marino caves in Sardinia

In the north west of Sardinia, close to Porto Conte bay, Alghero territory, there are more than 300 caves above and below water, with about 30 large, and many smaller, underwater sea caves in the limestone cliffs of Capo Caccia and Punta Giglio. The Nereo Cave is the most important and is considered 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. There is a fresh water cave of more than 110 m (360 ft) depth in this area.

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.

Jordbrugrotta (also known as Pluragrotta) is a cave in Rana, Norway.[40] It is the deepest cave in Northern Europe.[40]

Cave divers occasionally visit Jordbrugrotta which is the most dived cave in Scandinavia. Most of the other approximately 200 caves in Rana are not suitable for diving, and formation of caves has been limited due most of the rock being granite. Another diveable cave nearby is Litjåga. Damming of Kallvatnet made diving in Jordbrugrotta possible. There have been multiple cases of fatalities and injuries among visiting cave divers, but the accident rate is not out of proportion with the number of divers. The cave's passages were formed by the river Plura's flow through porous limestone.[41] Rock formations include marble.[42][40] Visibility in the cave is good.[43]

• Slovak Opal Mine, near Prešov. The mine consists of around 22 km (14 mi) of tunnels; with some measuring as deep as 150 m (490 ft).

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).

The caves and caverns of Grand Bahama contain an immense underwater cavern with a vast flooded labyrinth of caverns, caves and submerged tunnels that honeycomb the entire island of Grand Bahama 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 Bahama 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 limestone. 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.

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 about 1,800 m (6,000 ft) 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.

Safety concerns in Dominican Republic

An important safety issue on the island is untrained cave diving, principally led by unprofessional dive stores and guides risking their customers' lives. Unprofessional and unsafe practices of dive guides may be reported to the relevant dive agency and to the Dominican Republic Speleological Society.[44]

Yucatán Peninsula

While there is great potential for cave diving in the continental karst throughout Mexico, the 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 Cancún 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 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.

The underwater speleothems in the Yucatán Peninsula are fragile. If a diver accidentally breaks a formation, it will not reform as long as the cave is underwater so active cave conservation diving techniques are necessary. The Quintana Roo caves are extremely complex with anastomotic interconnected passages. When diving through the caves, they 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 Carwash, Naharon and Maya Blue, and to central Mexico where resurgence rivers such as Rio Mante, and sinkholes such as Zacaton were documented.[45]

Entrance to Dos Ojos

In the Yucatán, the 1980s ended with the discoveries of the Dos Ojos and Nohoch Nah Chich cave systems which led into a long competition of which exploration team had the longest recorded underwater cave system in the world at the time.

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.

By the mid-1990s a push into the central Yucatán Peninsula discovered a large number of deep sinkholes, or pit cenotes, such as Sabak Ha and Utzil, and deep caves such as Chacdzinikche, Dzibilchaltun and Kankirixche that have since been explored and mapped. These deep caves of the central Yucatán remain largely unexplored due to the number of cenotes in the State of Yucatán, and the depths, which require technical diving techniques or rebreathers. At the end of the last millennium closed circuit rebreathers were used to explore these caves.

By the end of the 1990s, The Pit in the Dos Ojos cave system located 5.8 km from the Caribbean coast had been discovered, and by 2008 it had been dived to 119 m deep. At that time, technical diving and rebreather equipment and techniques became commonplace.

By the turn of the millennium the longest underwater cave system at that time, Ox Bel Ha was established by cave diving explorers whose combined efforts and information helped join segments of previously explored caves. The use of hand held GPS technology and aerial and satellite images for reconnaissance during exploration became common. New technology such as improved rebreathers and diver propulsion vehicles (DPVs) became available and were utilized for longer penetration dives. In January 2013, Ox Bel Ha included 242 km of underwater passage (see QRSS for current statistics).

Active exploration continues in the new millennium. Most cave diving exploration is now conducted on the basis of "mini projects" lasting 1 – 7 days, and occurring many times a year, and these may include daily commutes from home to jungle dive base camps located within 1 hour from road access.

Starting in 2006 a number of large previously explored and mapped cave systems have been shown to be connected using sidemount and often no-mount cave diving techniques to pass through tight cave passages, indicating the largest known connected underwater cave system on the planet, Sac Actun, which is 220 km long (see QRSS for current statistics).

Many cave maps have been published by the Quintana Roo Speleological Survey (QRSS).

Central and Northern Florida

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 United States, The Leon Sinks cave system, near Tallahassee, Florida, has multiple interconnected sinks and springs spanning two counties (Leon & Wakulla).[46] 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 United States 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 120 m (400 ft)[47] The current deepest known underwater cave in the United States as of 2013 is Phantom Springs Cave located in west Texas. Phantom Springs has been explored down to 141 m (462 ft) in water filled cave passages.[48]

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 joint 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.

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.