How Spelunking Works

By: Dave Roos
Caves, like this one in Cueva de Villa Luz, Mexico, offer some amazing views for those willing to take a chance and go inside.
Stephen L. Alvarez/National Geographic/Getty Images

There's just something about a cave. It represents nature's final frontier -- a subterranean universe of mazelike passages, tight crawl spaces, vast chambers, deep crevices, cascading waterfalls, bizarre creatures and extraordinary natural sculptures just waiting to be discovered.

Spelunking is the recreational sport of exploring caves, but no one really calls it spelunking anymore. The acceptable term -- and the one we'll use here -- is caving.


Caving, like rock climbing, is as adventurous as you want it to be. There are family-friendly caves you can stroll through on a paved path. And there are others that require hundreds of feet of face-in-the-dirt crawling and rappelling down bottomless shafts.

There are thousands of caves in the United States, and more than 100 are open to the public for guided tours and expeditions [source: National Caves Association]. More than 200 U.S. caving clubs offer organized excursions to remote caves, teach advanced caving skills and participate in cave conservation.

Humans have been drawn to caves since ancient times. Modern archeologists have found evidence that ancient people viewed caves as sacred locations in which to carry out important religious rites. In prehistoric times, caves were attractive dwellings that offered stable interior temperatures and protection from harsh weather and other humans. In more recent history, caves have served as hiding places for stashed treasure, ideal environments for aging cheese and wine, and excellent natural labs for scientific discovery.


All About Caves

Caves like this one in coastal Australia are formed over long periods as water eats away at the limestone underground.
Sam Abell/National Geographic/Getty Images

A cave is any kind of natural, hollow, underground passage or enclosure with an opening to the surface. Caves are most commonly found in what's called a karst landscape, characterized by sinkholes, substantial underground aquifers and active subterranean drainage. Around 20 percent of the United States qualifies as karst [source: National Caves Association].

Caves are formed by four basic processes:


  • The majority of caves are limestone caves. These form when rainwater seeps down through the soil, picking up extra carbon dioxide. The result is a weak acid called carbonic acid. The water collects in underground aquifers where it slowly eats away the limestone. Some limestone caves are also formed by large amounts of running rainwater which carves away at the rock in a process called corrasion, or erosion by abrasion [source: Nova].
  • Only very recently have researchers discovered that microscopic bacteria have helped form some of the most impressive caves in the world. Bacteria called extremeophiles (creatures that thrive in "extreme" or highly toxic conditions) feed off of deep underground oil deposits. After eating a big meal, they expel hydrogen sulfide gas that bubbles up through the groundwater, picking up extra oxygen to become sulfuric acid, a powerful corrosive agent. Other bacteria live in the caves themselves, feeding off hydrogen sulfide to make even more sulfuric acid.
  • Pounding waves eat away at weak points in seaside cliffs forming caves with large overhanging ceilings. Most sea caves are carved from sandstone or limestone.
  • Lava tubes are created when the sides of an active lava flow cool first, forming a crust that slowly merges to cover up the still-liquid center. When all the liquid lava flows out, only the hardened tube is left. If part of the tube ceiling collapses, you have an opening to a lava cave. [source: Nova]
Educational signs in Virginia's Luray Caverns remind visitors that stalactites build downward from the ceiling and stalagmites build up from the floor of a cave. A good mnemonic device: Stalactites cling "tight" to the roof.
Alan Band/Fox Photos/Getty Images

Stalactites (the ones that hang down) and stalagmites (the ones that point up) are the best-known examples of speleotherms, also called cave formations. There's an astounding variety of speleotherms, some with oddly descriptive names like fried eggs and bacon. When carbonic acid eats away at limestone, it creates the mineral calcite, which is then carried by rainwater into the cave. When this rainwater drips onto the floor of a cave, it very slowly deposits bits of calcite until a stalagmite is formed. Other speleotherms are formed by calcite being precipitated in brilliant patterns and crystalline formations on cave walls, ceilings and floors.

There are three different classifications of animals that live in caves:

  • Trogloxenes are temporary visitors that live in and around the entrances to caves. Bats are the most famous trogloxenes, but the list also includes bears, bobcats, raccoons, cave swallows and pack rats.
  • Troglophiles spend most of their lives in caves, but occasionally wander out for food. Examples would be salamanders, crickets, flatworms and different species of spiders and daddy longlegs.
  • Troglobites live their entire lives in the pitch-black depths of dry and sea caves. All are blind and some don't even have eyes. Examples are the Ozark blind salamander, the Tooth Cave spider and Tooth Cave beetle, cave fish and blind shrimp [source: U.S. Geological Service]

Cave conditions vary dramatically depending on how the cave was formed and where it's located. Some caves are wet and muddy; others are dry and dusty. The temperature of a cave is very stable. It's always the average annual temperature of the surface above the cave [source: National Speleological Society].


Why Go Caving?

Working in Honduras, American speleologist Matthew Kalch copies down markings found on a seashell discovered in the Hato Viejo cave in 2006.
Elmer Martinez/AFP/Getty Images

For enthusiasts, caving carries the lure of the unknown and the thrill of discovery. In a small group -- and usually with a trained guide -- you'll enter a labyrinthine world of narrow pathways and tight crevices, lit only by the yellow glow of your headlamp. Depending on the cave, you may have to wade through waist-high water or scale up rocky walls. If you're lucky, you'll emerge in a large underground chamber filled with dangling stalactites and adorned with colorful, intricate calcite deposits. Half the fun is getting back out.

But not all cavers are in it just for kicks. Speleologists are scientists who study caves and their unique ecosystems. Some scientists research the rare and yet undiscovered creatures that make their homes in the furthest reaches of caves. An example is the emerging field of extremeophiles, microbes that thrive in conditions that would be lethal to humans. It's believed that these creatures could help us understand the earliest life forms on Earth [source: National Speleological Society].


Cave archeology can be another exciting reason to go caving. Because caves have served as sacred ritual and ceremonial sites for many world cu­ltures, and because they're relatively protected from the elements, they often contain well-preserved examples of ceremonial vessels, clothing and burial objects. Some of the most famous archeological caving finds have been the remarkable prehistoric cave paintings in places like Lascaux, France.

Some dedicated cavers work hard at cave preservation and conservation. They realize that caves are homes to fragile ecosystems and delicate calcite structures that can easily be destroyed by careless "spelunkers" or deliberate vandals. Cave conservationists might block off entrances to particularly vulnerable passages or help educate beginning cavers about proper caving etiquette.

Now let's look at some of the best ways to get started on your caving adventure.


How to Get Started Caving

Chinese tourists take a tour of Asia's largest cave, Huanglong (Yellow Dragon) Cave in Zhangjiajie, China. Tours like these are great ways to learn more about caving.
Goh Chai Hin/AFP/Getty Images

The best way for beginners to begin caving is to take a guided caving tour. Many of the larger, better-known caves in the United States have self-guided tours where you simply follow a paved or dirt path through easily accessible, well-lit passageways and rooms. If you want to explore the more remote corners of caves, you'll have to sign on with a guided group tour.

Guided tours vary considerably in difficulty and price. All of the major U.S. caves have Web sites where you can explore your options. Carlsbad Caverns in New Mexico, for example, offers ranger-led tours of Kings Palace that require nothing more difficult than walking up a steep slope and guided explorations of the Spider Cave, which requires extensive crawling through dusty, tight spaces. Guided tours range in price from $8 for an hour-long trip to more than $50 for an all-day excursion [source: U.S. National Park Service].


Kids and ca­ves are an excellent combination, particularly on guided trips designed for children. Caves tap into a child's natural curiosity and allow them to show off their crawling, climbing and squeezing-through-small-spaces skills. Caves are also excellent opportunities for science education in an impressive setting. Most major caves support children's education programs for schools and private groups.

Vertical caving uses ropes and other rappelling and mountaineering equipment to lower cavers into deep vertical shafts. Beginners are advised to attempt vertical caving only with trained, certified guides.

K. Gokce Okumus dives in a cave near Kemer, Turkey. Cave diving is an opportunity to marvel at the wonders of nature underwater, but shouldn't be attempted without proper training, certified guides and special equipment.
Tarik Tinazay/AFP/Getty Images

Cave diving -- the exploration of underwater caves -- is not for beginners. Even seasoned scuba divers shouldn't attempt cave diving without the proper training and without specially certified guides. Cave diving requires different equipment, techniques and a unique mindset that very few divers possess. While the rewards of cave diving can be magnificent, it's also potentially deadly.

If you get hooked on caving and want to go beyond the basic guided tours and touristy spots, you might want to join a caving club. In the United States, the National Speleological Society sponsors more than 200 caving clubs known as grotto­s. Caving clubs organize training and excursions with an emphasis on cave conservation.


Caving Equipment

The drop in Ellison Cave's Fantastic Pit is 586 feet (179 m). Beautiful, yes, but dangerous without the right equipment.
Michael K. Nichols/National Geographic/Getty Images

The single most important piece of caving equipment is your light. Experts recommend that you bring three independent light sources. The most basic is the head-mounted lamp that straps securely onto a helmet. Other light sources could be handheld flashlights, glow sticks or small LED lights. You should carry a few extra bulbs and batteries for each light source.

Your helmet should meet the stringent safety standards of Union Internationale des Associations d'Alpinisme (UIAA) or European Community (CE) certification. And make sure your headlamp fits tightly and securely on the helmet before you leave the house.


What you wear while caving depends on what kind of cave you're going to visit. A lot of caves are pretty cold -- in the 50s Fahrenheit (10-15 degrees Celsius) -- so you'll want to dress in layers. The National Speleological Society recommends synthetic fabrics like nylon and polyester over cotton because synthetics tend to dry faster if they get wet and are more resistant to the scrapes and snags common to caving.

Find out everything you can about the cave you're going to explore. If there's a chance you'll get very wet, you'll want to bring a change of clothing. Some other clothing items you might want to consider are waterproof hiking boots, gloves, thermal underwear, and knee and elbow pads for extended crawls.

You'll need to bring enough food and water for the expected length of the trip and some extra, just in case. If you have a map of the cave, make copies and give one to everybody on the trip, even if you have a guide.

You'll want a small first-aid kit for cuts and bruises. Make sure that everyone brings any medication that he or she needs to take on a regular basis. You'll need enough large plastic garbage bags to hold any food waste and dirty clothing.

A general rule of cave conservation is not to leave anything -- including human waste -- in the cave, so everyone will need a plastic bottle for urine, toilet paper and a small, crush-proof plastic container for "number two."

Some other useful equipment for cave exploration is a camera with a flash (consider disposable models to avoid damaging expensive equipment), a magnifying glass, pen and paper, and the universal solution for any problem -- duct tape.

Now let's look at some important safety considerations when caving and the best techniques for protecting yourself and your group.


Caving Safety and Tips

Six British speleologists were trapped in Mexico's Cuetzalan caves network in 2004. They were rescued but deported.
Rafael Duran/AFP/Getty Images

In 2007, the National Speleogical Society received 24 accident reports related to caving and cave diving in the United States and Canada [source: National Speleological Society]. This represented only a fraction of the annual accidents, as many go unreported. Most reported accidents involved minor injuries, but five were fatalities (four of them while cave diving).

Caving, like other outdoor sports, can be a perfectly safe, family activity when cavers are educated, prepared and treat caving safety with the seriousness it deserves. First of all, it's important to know the most common causes of caving accidents and injuries:


  • Getting lost in the cave
  • Running out of light
  • Hypothermia (dangerously low body temperature)
  • Flooding of passages
  • Slipping and falling
  • Falling rocks
  • Falling into crevices and pits [source: National Speleological Society]

There are several things you can do before you even leave the house that will help you stay safe while caving. First of all, never go caving alone. A small group of 4 to 6 is preferable to a large group with potential stragglers. If you're not hiring a guide, make sure that at least two people in your group are experienced cavers who know the cave very well. Most important of all, let several people know about your caving plans -- exactly where you are going, who is going with you and when you plan on being back home.

Make sure you have everything you need, most importantly extra bulbs and batteries for light sources, ample food and water, good shoes and plenty of warm clothing.

When you begin caving, always stay together -- another good reason to keep the group small and manageable. If you have a larger group, break it up into small sections that can each be responsible for themselves. Keep the slowest caver in the front of the group, so you don't run the risk of leaving anyone behind. Even in a relatively easy cave, stop frequently to check how everyone is doing.

A basic rule of thumb while caving is not to take any unnecessary risks. Always look for the easiest way to navigate the cave. If you have a choice between walking 10 minutes around a crevice or jumping straight over it, go around. Any injury, no matter how small, is magnified by the difficulty of evacuating an injured person from a cave.

If someone does get injured and can't make it out of the cave on his or her own, don't leave that person alone. Send two or more people to go get help from police or paramedics. Make sure the people who leave know exactly where the injured person is and the extent of his or her injuries. Also make sure they have car keys or access to cell phones. Leave plenty of food, water, extra clothing and backup light sources with the people who stay in the cave.

If you get hopelessly lost in a cave or if your light runs out, the best thing to do is stay put and try not to panic. This is why it's so important to let several people know about your caving plans. When you don't return, they'll know exactly where to direct rescue personnel. If you're lost and you keep moving, you'll make it even harder for rescue workers to find you.


Lots More Information

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More Great Links


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