Hell’s bells and other Yucatan cave specials

PIERRE CONSTANT has been in Mexico, ever-keen to delve deeper into its cenotes – especially at a time when at least some of them could be coming under threat. He wrote the report and took all the pictures…

Yucatan is a fascinating land, not only for its culture, its unique nature and wildlife or the ancient archaeological sites of the Mayans, but because it is a cave-divers’ paradise.

It was my fifth visit in the past five years. Back in 2017, I took part in a TDI sidemount cave course in Playa del Carmen. In 2018, I dived the cenotes around Merida, and returned the following year for more. 

In 2020, my cave-training was pushed a step further with a stage course in Playa and DPV training in Tulum. It was more exciting but challenging – at this level, you can‘t use an underwater camera because you need both hands to deal with the equipment. 

You can hardly pretend to have done Yucatan after a single trip. An Open Water Diver in a cenote is allowed to do only cavern dives, with daylight always in sight. Anything in an overhead environment requires specific cave training followed by advanced cave training, all well before reaching full cave sidemount level and so on. 

Most divers experiencing cenotes for the first time would enjoy only limited access, and get to know the classic sites dived by most tourists. With thousands of cenotes from which to choose, it would take a lifetime to explore it all.

The most dedicated, hardcore, resident cave-divers will go on on discovering new cenotes every now and then, or push further into the unknown reaches of existing cave systems. 

Gondwana

Before the break-up of ancient Gondwana, comprising the continents of North and South America and Africa, Yucatan was temporarily attached to what would one day become Venezuela. As the proto-Atlantic and Gulf of Mexico began to form 140 million years ago, it broke away and became an isolated plate. 

Rotating anti-clockwise and drifting west for the next 50 million years, Yucatan collided with Mexico. A fracture zone emerged on the east of the peninsula and the Yucatan basin was formed.

The Yucatan plateau was made from Cretaceous limestone, with no surface rivers but with subsoil through which water seeps. A meteoritic impact that left a vast crater in Yucatan and caused the world’s second mass extinction also created a vast web of fractures underground, and over millions of years rain dissolved the limestone further to create subterranean water streams and sinkholes. 

The world’s longest underground rivers, classified as ‘systems’, are found in the coastal region of Quintana Roo, east of Yucatan. 

Ice Ages affected the peninsula between 150,000 years and 20,000 years ago. The last one saw the arrival of people from Asia via a land bridge over the Bering Strait. In the extreme cold conditions, they were drawn to live underground. Sea level was 65m lower than it is today.

Prehistoric animals such as bears, giant ground sloths and sabre-tooth tigers shared the caves, while above ground roamed mammoths, mastodons and glyptodonts along with llamas, camels and horses.

At the end of the last Ice Age, about 8,000 years ago, the sea level rose and most of the caves were flooded by seawater. Freshwater from rains rose to the top as a distinct layer, forming the blurry halocline where salt and freshwater mix between them. 

Much later, caves played an important role in Mayan culture. The word cenote originates from the Mayan dzonot, meaning chasm or cavern filled with water, symbolising an entrance to Xibalba, the underworld of the dead but also the fertile place where life originates – a symbolic pathway between Earth and the infraworld. 

Pottery has been found in the sinkholes, along with the remains of sacrificial offerings such as young girls. Cenotes sometimes provided burial grounds for older people or dignitaries. Nowadays, Mayas consider the cenotes with respect, as a place for cave spirits.

My refresher

The Air France flight landed in Cancun at night. I sorted out the hire car and, with rain on the highway, reached the hotel at Playa del Carmen an hour later, making it to bed well after midnight. 

A transition day was compulsory, to prepare my diving equipment and underwater camera. I was to meet Max, my cave-diving guide, the next day. We had met four years earlier on the Merida trip. 

Very professionally, Max started with a thorough revision of my gear, complaining about some aspects such as the absence of a long hose on my second regulator, a line-cutter and spools.

I had not been cave-diving for two years, so a refresher was required. I felt a bit of tension at the thought of being in an overhead environment again and knew that I needed to concentrate fully. When not practising regularly, things can get forgotten, and with this line of activity there is no room for error. 

I had done 25 cenotes / caves by now and was looking for something new, exciting and, if possible, ‘special’.

Our initial drive took us north to Puerto Morelos, from where we turned west on the Ruta de los Cenotes. The Yucatan jungle is rather dry, with a maximum tree height of 15m, and it is home to amazing birds and fascinating animals such as jaguars and pumas, which Max likes to photograph using infra-red cameras placed in remote spots.

Zapote: tree and bells

We planned to dive Zapote, an hourglass-shaped sinkhole that proved rather dark once we were under water, with a poisonous layer of hydrogen sulphide 30-35m deep. From this, the trunk of a 4,500-year-old zapote tree emerged like a ghost, growing from the 54m-deep bed. 

What makes Zapote unique are the “Hell’s bells”, or inverted mushroom-shaped stalactites, that hang from the walls. These formations are made in water through a biogeochemical mechanism, though it is bacteria trapped in the hydrogen sulphide layer that creates the bells.

Known as ‘extremophiles’, these bacteria thrive in extreme environments, processing sulphur and raising the pH of the water to create unique formations above the halocline. So the bells are alive on the outside and sulphur-powered organisms contribute to the calcium build-up. 

The bells require a low-light environment and form only near the layer down to 35m. In 2020 a researcher theorised that they were formed that way because of carbon dioxide bubbles rising from the deep and getting trapped against the almost-horizontal ceiling. 

Radiometric dating of some of the bells indicates that they grew during the middle and late Holocene period. Some of these funny CO₂-consuming mushrooms can reach 1-2m long and 80cm wide, and neighbouring sinkholes contain similar structures. The zapote tree itself displays “baby bells”.

Maravilla dome

Cenote Maravilla lay nearby – a circular sinkhole, partially blown up by the owner, with a steep wooden stairway climbing down into it. Once under water, the conspicuous dome shape became apparent.

There were no formations worth mentioning but there was great visibility and a magnificent shaft of early-afternoon light that pierced into the deep. 

The site offers ambience for underwater photography as well as being a training site for freedivers. Water temperature was 25°C.

We headed south for the next couple of days, to near Dos Ojos and the Sac Actun system. This was established in 2018 as the world’s longest-known underwater cave system, connecting 187 cenotes and a mind-blowing 365km long.

In March 2008, three members of the Proyecto Espeleogico de Tulum explored the Hoyo Negro pit and found the remains of a mastodon at 60m. At a depth of 43m, the skull and bones of a teenage Mayan female, a paleo-American now referred to as Naia, was dated back 12-13,000 years.

Secret Water

At Cenote Tak Be Ha (Secret Water) our tanks were brought by rope through a chimney hole in the ceiling to water level. A steep stone stairway allowed for walking down into a large, wide chamber, with lots of decoration and artificial light.

Further away, an 8km potholed dirt road led through the forest to the Concha site, a half-collapsed sinkhole with a huge Alamo tree extending its roots like the tentacles of a crawling octopus. The jungle feel was overwhelming. 

Access to the water was very shallow over white sand. Outside the cave were tall leafy trees and beautiful motmot birds flew by. Sneaking through a narrow gateway in the limestone, we immediately plummeted to a depth of 14m for the rest of the dive. Visibility was gin-clear. 

At the first T-junction we followed the line left, meandering through various chambers with columns, stalagmites, stalactites and helictites hanging from the roof like darts. 

After 30 minutes, as my gauges displayed 140 bar, Max pointed out an overhang above the cave-floor. To my surprise, I saw the full skeleton of a giant ground sloth, Xibalba oviceps, lying where it died more than 10,000 years ago during the last Ice Age. 

On the way back, Max drew me aside into a small chamber. A little signboard bearing the number ‘285’ marked the bones of a small gomphothere, Cuvieronus tropicus, an impressive mastodon with straight forward-facing tusks.

Following the narrow jungle trail back to the car with a tank on my shoulder, I noticed with awe a tiny snake coiled neatly on a rock and rushed back to take a photo. 

“Be very careful, that is a nauyaca!” warned a passing Mexican cave-diver. The ultimate pit viper Bothrops asper is a highly poisonous snake also known as the fer-de-lance that can spit venom over distances up to 2m. “A friend of mine got bitten, and remained in intensive care for four days…”. 

I was no more than 50cm away when I took the shot. Soon after, Max came across a hairy Yucatecan tarantula, Brachypelma epicureanum, on the forest floor. Black with a reddish abdomen, it swiftly hid in its hole.

Tannin spectacular

On my fourth day of cave-diving Max took me to one of his favourite sites, 20km from Tulum and 8km inland. Another tarantula welcomed us at the car park as we prepared our gear and tanks, and on the 50m stroll to Koi cenote a 60cm Southern Yucatan variable coral snake, Micrurus apiatus, slithered across the forest floor. 

Dark red with black bands outlined with narrow yellow bands it was a gorgeous creature, rather shy but poisonous. 

A rusty iron stairway spiralled down into the cenote’s small opening, straight to the water table. Cement blocks helped when laying down the tanks in shallow water. There was a wide dome, a low ceiling with stalactites and a few bats – the floor was made of black, volatile bat guano, while the walls were white limestone. 

At a depth of 10-14m, Max led me under water to Xuxi cenote. “I’ll show you something special,” he had said, and now I marvelled at the sight. 

During the rainy season, the presence of soil and leaves results in a lot of tannin, seeping down in the water subsurface. This translates into breathtaking reds, oranges, yellows and greens in the water column – an apocalyptic vision. We pushed further into various chambers.

After a picnic of tacos, we returned to Koi but this time jumped left and then right to an indistinct pile of elephant bones that we reached after a 30-minute swim. Little white INAH (Instituto Nacional de Antropologia y Historia) cones had been placed as indicators for scientific investigation.

On to Xulo

South of Tulum, shortly before Muyil, is Uku Cuzam, also called Xulo after the local Maya owner. Originally explored by Alvaro Roldan in 2013, it is now connected to the Systema Caterpillar and downstream from it. “A five-star cenote!”, exclaimed Max. 

An elderly man named Emilio was the caretaker of the place, along with his two dogs. After paying the 300 peso entry fee (£11.60), we proceeded down a flight of steps into the low-lying cenote. The water table was in darkness and I had to turn on my helmet light to set up. 

Very quickly the line plunged to 10m and highly ornate chambers with awesome pillars, showers of stalactites, stalagmites in the shape of fingers or chandeliers, and walls of draperies and helictites appeared. 

The enchantment was short-lived. Max suddenly jumped to the right, into a corridor of restrictions under a low ceiling. Turning round was unthinkable, and I needed to place my camera with extended strobe arms sideways to proceed forward. It felt rather uncomfortable. 

Eventually we caught up with the main line running through a side-tunnel. Another jump and it was back to base from there, in a 56-minute dive. The strobes stopped working properly and I suspected low batteries. I decided to leave the camera behind for the next dive.

This proved a wise decision, as my dive-guide made a jump to the left, after a third set of double arrows, and led me through restrictions and very narrow passages under the roof, snaking sideways non-stop. He even signalled me to stop in key moments so that he could run a video of me with his GoPro.

After 67 minutes, happy with my performance and buoyancy, Max shook my hand positively before exiting. 

Sitting peacefully in front of his wooden shack, Emilio was waiting for us with a caguama, a 1-litre bottle of beer, his dogs resting flat on the ground. A couple of toucans flew overhead, landed on a branch to peek at us and took off as soon as I grabbed my camera.

Alexis Passage

Based in Tulum for the next three nights, my last dive-day was with Elliot and the site Cenote Regina. Originally explored in 2004 by Robbie Schmittner, it is now connected to the Sistema Ox Bel Ha (via Mayan Blue) but poorly known, except to the lucky ones! 

A large pool of water with a wooden deck was surrounded by palm trees. The murky entrance-hole started into a restriction, then opened into a rather dark cave with a wide tunnel. The plan was T-left, T-left until we plunged deep into a canyon at a depth of 25m.

All of a sudden, it lightened up as if by magic in the Alexis Passage, an underground riverbed in white and light blue where the halocline occurs, and everything was blurry for 30 seconds. It was a mesmerising environment – but it was already time for me to turn around.

For the next dive, the plan of action was T-right, T-left and T-right. Once again, we dropped into a deep saltwater passage beyond 18m. 

As I gazed at Elliot disappearing into the haze of the halocline, my right ear became painful under pressure and I realised that I couldn’t get any deeper without risking serious trouble. This could become a nightmare in seconds. 

I waved my light frantically at Elliot, until he understood my signal as calling off the dive. Better safe than sorry.

Also on Divernet: DIVING INTO MEXICO’S SEDUCTIVE UNDERWORLD, DIVERS LOCATE AMERICAS’ EARLIEST OCHRE-MINE, DIVERS FIND EXTINCT MAMMALS IN BLACK HOLE, BE THE CHAMP! – CENOTES FORMATIONS