Exploring the Last Frontier: Diving Mexico's Yucatan Cave Systems

By Chris Kostman

Originally published in Fitness Plus, Vol. 7, No. 5, May 1996 and Oui, Vol. 27, No. 6, June 1996. Photo of the author by Steve Gerrard.

It's the Star Trek Syndrome.

While hundreds of thousands of vacationing scuba divers gleefully dive the warm, clear, friendly waters around the Mexican island of Cozumel, just off the coast from the resort town of Vegas-like Cancun, a few hundred instead head for the water-filled inland caves a short trip south.

A not unreasonable parallel would be Nepal. While hiking boot and day pack-toting tourists numbering in the hundreds of thousands go trekking on the lesser slopes of the Himalayas each year, a few hundred instead prepare an assault on the world's tallest peak, Mt. Everest.

Trekking is for the other people. So is open water recreational diving.

Welcome to cave diving, a discipline built around the overwhelming desire, need, or even compulsion "to boldly go where no one has gone before."

But cave divers share more than the credo with the explorers on Star Trek. Cave divers are also dedicated to science, engineering, self-sufficiency, and a thoughtful sensitivity to the environmental, ecological, and political terrain through which they travel. The Cave Diver's Prime Directive: "Take only pictures. Leave only bubbles."

My Voyage Below Ground

More than anything, cave diving requires specific education and training built first upon a foundation of traditional open water diving. Before venturing below ground, my open water diving had included beach dives, boat dives, severe condition dives along the 50 degree Northern California coast, tropical dives in Hawaii, the Indian Ocean, and the Persian Gulf, night dives, reef dives, kelp forest dives, drift dives, blue water dives, deep dives to over 100 feet, non-penetration wreck dives along the mid-Atlantic, and two years of serving as an Assistant Instructor of Scientific Diving at U.C. Berkeley.

My desire to always do more, go further, and keep learning and training next brought me to Mexico to learn cave diving from one of its original pundits, U.S.-native Steve Gerrard. He's a Floridian through and through (a huge fan of the Florida State University Seminoles) and one of the original pioneers of cave diving in Northern Florida's spring systems. Gerrard also organized and led one of the first (and few successful) cave diving rescue missions, featured on "Rescue 911." He also writes extensively on the subject, works closely with the various training organizations built up around cave diving, and has trained many of the top cave divers. He's also a leader of the Cenote Dos Ojos exploration team, helping to map the innumerable tributaries of this twenty mile long Mexican cave system that is the world's longest.

Gerrard's operation, AquaTech, is housed at Villas DeRosa, a quaint little tourist resort in Aventuras Akumal on the Caribbean coast of the Yucatan, just north of Tulum. It's just a one hour drive south through the jungle from Cancun, but worlds apart. In a word, the Tulum area is still unspoiled. Gerrard and his colleagues, Tony and Nancy DeRosa, aim to keep it that way.

Training, Training, and More Training

I had signed on for the full cave diving treatment. That would take me through all three levels of cave training and make me "fully certified" in one busy week. But I would quickly learn that cave diving is not a certification card, but a lifestyle, a commitment, an all-consuming avocation.

It was a whirlwind week of diving. We did sixteen dives for a total bottom time of over 700 minutes. Gerrard gave me formal and informal lectures, some while bouncing through the jungle in his van and others in front of a chalkboard, video monitor, or projection screen. His command of a host of topics ranging from physiology to safety to mindset and more was awesome, although his modesty and strength at understatement were equally impressive. I was truly learning at the feet (fins) of a master. What an opportunity!

A Little Geology

First I learned that cave diving is one of the most equipment-dependent pursuits on the planet. Why? Because in cave diving, one can literally be miles from the nearest source of light or air. You see, Mexico's cave systems ("cenotes") are not water-filled holes in the ground, but huge, subterranean, water-filled rivers zig-zagging through the limestone crust upon which the Yucatan jungle thrives.

Imagine swimming through tunnels filled to the top with crystal clear water. In fact, the water is so clear that only the sight of your dive buddy's bubbles reminds you that you are indeed not flying. The tunnels and chambers range in size from a few feet to hundreds of feet around. They are filled with wondrous geological formations dating to the last Ice Age, when the ocean levels were lower than today, leaving these incredible cave systems devoid of the rivers that formed them and that resumed flowing after the polar ice caps melted. During that Ice Age interim, when the caves were not water-filled, incredible stalagmites, stalactites, columns, waterfalls, soda straws, and other "decorations" were built by the slow dripping action that builds these geological beauties, grain of calcium carbonate by grain of calcium carbonate. And now these incredible sights are frozen in time, hidden from the view of everyone but the intrepid cave divers.

The open water springs poking through the limestone crust that are the portals to the cave systems are as varied as the caves themselves. Some are nice round pools immediately accessed from a road. Others are small lakes found only after a long trek on foot through the jungle. One is a tiny hole in the ground that looks very much like a well and provides only enough room for one diver at a time to push feet-first through a ten foot long, water-filled tube into the actual cave system.

The Well-Dressed Cave Diver

From head to toe, here's a basic look at what it takes to dive Mexico's water-filled caves:

  • Neoprene hood to keep warm and protect head. (Some wear helmets.)
  • Mask. (Some carry a spare mask as well.) No snorkel since there's no surface on which to snorkel.
  • Neoprene, full body wetsuit, such as the custom suits by Monterey Bay Wetsuits with 1/4" jacket and farmer john.
  • Dual, aluminum, 80 c.f. (or bigger) gas cylinders, clearly marked with contents ("air," "nitrox," etc.) with dual manifold, isolator valve, and DIN first stage valves.
  • Two second stage regulators, one with a seven foot hose for buddy-breathing while swimming single file through tight spaces.
  • Backpack with back-mounted buoyancy compensators ("wings") for proper buoyancy attitude and streamlining.
  • Weightbelt with ten to twenty pounds of lead, as needed.
  • One 12 volt, 50 watt floodlight with back or tank-mounted rechargeable battery pack.
  • Two backup battery lights, strapped to equipment in easily accessible locations.
  • U.C. Berkeley-style wrist gauntlet with depth gauge, compass, watch, knife, slate and pencil, and dive computer attached.
  • Two to five safety and exploration reels, containing many hundreds or thousands of feet of 24# nylon line. Also, several clip-on plastic arrows for marking direction to exit.
  • Tangent Delta Force Fins, short and flexible for maximum comfort, maneuverability, and propulsion.

Equipment is critical, thus redundancy and streamlining are two of the main watchwords of cave diving. Redundancy means that cave divers take two or three of everything critical. At the very least, that means two tanks of air with separate regulators, three light sources, and several reels of nylon line for marking the way in and out of the cave. Streamlining means that all this equipment has to not only not get lost or fall off, but provide as little hydrodynamic drag as possible and stay in close to the diver where it can't catch on anything. Getting snagged in a tight spot is not a good thing in cave diving. Running out of air or light is even worse, for there's no surface to head to as in traditional open water diving.

In the blink of an eye, you can be killed while cave diving. But if you are, it's probably your fault. And that's a good thing, because it means that you can learn how not to kill yourself.


Good scuba training, whether for cave diving or just open water diving, trains a diver to think and act instinctively, to not be dependent on equipment for life support, and to be fully aware of the surroundings. But where sport diving training generally fails at that mission, cave diving training excels at it.

Gerrard taught me how to design and set up my equipment in ways that avoid the pitfalls of traditional equipment set-ups. The master also bequeathed to me special breathing, relaxation, and focus skills that would enable me to remain calm while diving, keep a clear head when faced with a challenge, and conserve my always precious gas supply. He also made me to understand the unique physiological and physical demands of cave diving, from how to walk miles through the jungle in a full wetsuit with 90 pounds of gear on my back (pour water in the wetsuit first) to how to squeeze through tight spaces in the caves (take off the tanks and push them through in front of me).

I even had to relearn how to kick while diving. With special, shorter and more flexible fins, such as the Tangent Delta model by Force Fin, I learned to kick softly and tidily. I needed to not only avoid kicking any of the beautiful geology, but also avoid stirring up the vision-blocking silt that layers the bottom of the caves. The big, open-legged, sitff-boarded kick so common among macho open water divers would not work here.

We also practiced innumerable emergency drills while in the caves. In one, I had to remove my mask, turn off all lights, breathe from Gerrard's spare regulator from his gas supply, and lead both of us out of the cave. This bleary-eyed quarter mile trek would have been impossible without the nylon guideline which we had strung into the cave on our way in, now held carefully in my hand as the only source of direction. In another drill, Gerrard led me several thousand feet into a cave, took me about fifty feet away from the guideline we had laid in place on our way in, then turned off all the lights. My job, while he hovered near the ceiling and watched my progress and location by observing my glowing compass on my wrist, was to find the guideline. No guideline, no exit, you're dead, it's that simple. In a real emergency situation, my life would depend on my ability to locate the guideline.

To fulfill my mission I had to focus all my attention on my surroundings, my kinesthetic and tactile sensitivity, my breath, and my mental recollection of the cave layout. I tied off a safety reel of nylon line to a nearby stalagmite, then swam out and back like the spokes on a wheel in search of the guideline.

It was so quiet, so dark, during this drill that Gerrard actually yelled through the water once to inquire if I was ok. I was ok, but it took me forty-five minutes to find that guideline.

Pushing the Limits

Time is of the essence in cave diving. There's always a finite amount of gas to breathe and certain physiological limits as to how much gas of what type can be breathed at certain depths for certain periods of time. (This is serious physics and physiology and insanely important to understand, practice, and be able to apply to real life and death situations.) Thus anything and everything is done to maximize the in-water time and efficiency.

One method is breathing special gas mixes other than air. The most common is nitrox, which is oxygen-enriched air. Instead of being 80% nitrogen and 20% oxygen like traditional sea-level air, nitrox has 30 to 40% oxygen. For deeper dives, too much oxygen or nitrogen becomes a problem, so a special gas called trimix, containing nitrogen, oxygen, and helium, is often used. The end result is the potential for safer diving, longer dives, quicker recovery, and shorter surface intervals between dives.

Physical training for diving also helps to push the limits. A high level of aerobic and muscular fitness, especially a low resting heartrate, are paramount to gas conservation and diving endurance. Flexibility, dexterity, and kinesthetic or proprioceptive awareness are also key to maneuvering the tight and environmentally sensitive cave systems. Slow, methodical breathing, working in tandem with a clear and calculating mind, also maximize diving performance.

Special equipment such as DPV's (diver propulsion vehicles) allow the divers to venture further, as do dive computers that monitor breath, gas supply, depth, temperature, and much more, then download the entire dive profile into a laptop computer after the dive. Sophisticated mapping and navigation systems also help to push the limits, as well as pave the way for other cave divers to follow.

Like Sir Edmund Hillary blazing the Everest trail for so many more to follow, Steve Gerrard and the other pioneers of cave diving have beautifully choreographed their explorations into the Floridian and Mexican cave systems. Although they have taken nothing but pictures and left nothing but bubbles, they have created a training and education program through numerous international agencies, as well as set critical standards of excellence and protocol, that allow far more mortal divers to follow their guideline into this final frontier.

Dive long and prosper.

Links for Cave and Technical Diving

International Association of Nitrox and Technical Divers Homepage

Immersed: the International Technical Diving Magazine Homepage

Aquatech / Villas de Rosa Homepage- The place to study and stay for Yucatan cave diving!

The Yucatan Cave System of El Jacindo Pat Homepage

Force Fins Homepage

More Diving Reading

SCUBA Diving's Life Lessons

The Force Fins Story: an Interview with "Finatics" Bob Evans and Suzanne Chess