U
li Kunz stared into the deep sinkhole.
Clear water sparkled at the bottom of the pit. T e photographer saw more than a pretty pool, though. He saw danger and adventure. He knew that this sinkhole, called a cenote, was the opening to a cave. Inside, this cave was dark as night. Water
filled it. Its tunnels twisted and turned like a maze. No light. No air. No hope if he got lost. Even so, Kunz got ready to dive in. He was
there with a team of scientists. T ey had work to do. T ey came to find out what lay hidden in these unique caves. What a thrill, Kunz thought, to take photos of this unseen world. T en he had another thought. So much could go wrong. His lights could fail. He could run out of air.
He could bump into the cave walls and stir up blinding dirt. He could get lost. Kunz and the team trained hard to stay
safe. T ey hiked in the jungle with their eyes closed. Only a rope guided them. T ey practiced letting go of the rope and finding it again. They swam through tight spots and tried not to touch anything. T ey learned to talk to one another only using hand signals. Now Kunz checked his air supply one last time. He checked his lights. T en he jumped.
UNITED STATES
Carving Caves Kunz was diving in the Yucatan Peninsula in Mexico. Above the ground here, jungle grows. Underground, hundreds of caves wind through the rock. Some caves stretch for many kilometers. Water fills them. T e land wasn’t always like this. Once, it
was a solid chunk of limestone rock. Year aſt er year, rain pounded the ground. T e water soaked through soil on top of the rock. As it moved through the dirt, the water
picked up carbon dioxide. T is gas turned the water into a weak acid. T e acid nibbled away the limestone. It caused a chemical reaction. It dissolved some rock. T is change is a form of weathering. T at’s when rocks are broken down into smaller pieces.
Flooded! Over millions of years, weathering carved gaps in the rock. Rainwater dripped in. Groundwater flowed through. Near the coast, ocean waves rushed in and out. T is moving water eroded the rock. T e
water carried bits of rock away. Bit by bit, this erosion made the gaps in the rock bigger and bigger. Many became caves. Yet not all of the dissolved rock washed
Yucatan Peninsula
PACIFIC OCEAN
away. Some dripped slowly. As it did, carbon dioxide escaped. T at let the rock harden again. New rocks formed. Some hung from cave ceilings like fangs. Some rose from cave floors like towers. Others looked like wrinkly curtains or even bells. T en, about 18,000 years ago,
Earth’s climate began to warm. Glaciers melted. Oceans rose. Rising water flooded the caves. It hid them from sight.
12 NATIONAL GEOGRAPHIC EXTREME EXPLORER
MEXICO
Gulf of Mexico
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