A cave is any natural hollow space beneath the earth that does not receive direct sunlight. Caves may have one room (chamber), or a complex maze of interconnected chambers and varying levels. Passageways range from small openings that require crawling, to giant galleries hundreds of feet wide. There are several different types of caves, as described in the following paragraph.

Caverns are created when subterranean limestone, dolomite or gypsum is dissolved by underwater streams or rainwater seeping down into the ground. Sea caves are formed by waves beating against shoreline cliffs. Wind caves are created from blowing sand eroding away weak spots in cliffs. Lava caves develop when lava flowing from a volcano cools and hardens on the surface, trapping a molten river of lava underneath that eventually drains out, leaving an empty tube. Some caves in mountainsides or cliffs are caused by the crumbling of soft rock lying beneath harder, overhanging rock. Caves can also be found along fissures, faults and gaps in piles of boulders.

Limestone caverns are well known for their strange and beautiful rock formations (speleothems). These water‑based caves are like underground fairylands displaying an unusual variety of icicles, pillars, curtains and other decorations created by mineral deposits resulting from dripping and evaporation. An “icicle” hanging from the ceiling of a cave is called a stalactite. One that grows up from the ground floor is a stalagmite. There is an easy way to remember which is which. The word “stalactite” has a “c” for ceiling. The word “stalagmite” has a “g” for ground. Dormant caverns are generally dusty and dry, and living caverns are humid and wet.

The temperature inside a cave is always cool, and some caves have ice in them. The surrounding rock walls function as a huge thermal mass, so a cave usually takes on the average year‑round outside temperature. A cave that has more than one entrance is said to be a “blowing” or “breathing” cave as the air moves between openings. The interior of a deep cave is completely dark since daylight does not reach beyond the cave mouth (entrance). Cave floors may be smooth or covered with broken fragments of fallen rock. Caves are often discovered when the ceilings of underground passages collapse, leaving a hole within a large pile of rocks called a “breakdown.”

People of all ages like to go cave exploring, a sport that is also known as caving or spelunking. Recreational cave hobbyists are spelunkers. Scientists who study caves are speleologists. Beginners can tour improved “show” caves where there are guides and electric lights. Serious cave enthusiasts should consider joining a local caving club or “grotto.” Then they can visit wild, undeveloped caves after gaining some experience.

A cave adventure is fun and exciting, but it can also be dangerous and must be done with care. Underground hazards include: running out of light, hitting your head, stumbling and tripping on irregular terrain, slipping on wet spots, getting cut on sharp rocks, becoming lost, developing hypothermia, being trapped in flooded passages, falling into holes, and having the ceiling collapse on you. Vertical shafts and deep pits requiring the use of ropes and climbing gear should be reserved for the most experienced cavers. Abandoned mines should never be entered.

All cave explorers need to follow certain safety rules. Wear warm clothes, sturdy boots or sneakers, leather work gloves and a hard hat or bicycle helmet. Battery‑powered head lamps are readily available and highly recommended as a hands‑free source of light. You should also have a waterproof flashlight in your pocket with a spare bulb and extra batteries. Candles and glow sticks are not a dependable light source. Flares should definitely not be used because of the smoke and fumes. Never explore a cave alone, and always tell someone on the surface where you are going and when you should be back. Bring a small first‑aid kit and plenty of water to drink, too.

Live caves shelter fragile underground ecosystems, and all caves are a unique and limited natural resource. Please respect cave environments and don’t spoil the down‑to‑earth experience for future spelunkers and explorers. This should go without saying: Do not light fires, mark walls, leave trash or camp in caves. Don’t touch or break rock or mineral formations. Don’t bring pets or glass bottles inside caves. Don’t disturb any cave creatures like crickets or bats that you may encounter. Leave only footprints, and take nothing but pictures. For this you will need a flash camera or a video camera with a low light setting.

How many caves are there in Arizona? You may be surprised. Find out next week.

Books

“The Adventures of Tom Sawyer,” by Mark Twain. (Read about the frightening experience of Tom Sawyer and Becky Thatcher when they get lost inside a cave in chapters 29‑32.)

“Journey to the Bottomless Pit: The Story of Stephen Bishop and Mammoth Cave,” by Elizabeth Mitchell. (If you toured Kentucky’s Mammoth Cave in the year 1838, your guide would have been 17‑year‑old Stephen Bishop, an African American slave.)

“Journey to the Center of the Earth,” by Jules Verne. (A scientist leads a small team on an expedition to the Earth’s core. They enter the crater of a volcano and follow the lava tubes down through the depths of the Earth.)

Web Sites

www.caverntours.com/classroom/cgp1.htm (A great lesson in cave geology and geography for grades K‑12. Includes experiments, activities, glossary and recommended reading.)

http://42explore.com/caves.htm (Learn about the geology and ecology of caves in this Web‑based unit study.)

www.fantastic‑caverns.com/research.htm (A Fantastic Caverns study guide on the science and history of caves, including quiz questions.)

www.caves.org (The National Speleological Society, an organization dedicated to cave study, conservation and exploration. Includes links to local caving organizations.)

www.cavern.com (National Caves Association, a nonprofit organization of publicly and privately owned show caves and caverns developed for public visitation.)

Teri Ann Berg Olsen is a home educator and author of the book “Learning for Life: Educational Words of Wisdom.” For more information, please visit www.knowledgehouse.info.