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 entrance to a cave. Inside, this cave was dark as night. Water


U


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 from Germany. T ey had work to do. T ey came to find out what lay hidden in this unique cave. 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. His air tanks could


run out. He could stray too far from the rope used to guide his way in and out of the cave. He could bump into the cave walls and stir up blinding dirt. T e team had trained hard to stay safe.


T ey’d hiked in the jungle with their eyes closed. Only a rope guided them. T ey’d practiced letting go of the rope and finding it again. T ey’d swum through tight spots and tried not to touch anything. T ey’d learned to talk to one another using only hand symbols. Now, it was time. Kunz checked his lights. He checked his air supply. T en he jumped.


li Kunz stared down into the deep


Carving Caves T e place where Kunz was diving is in Mexico. Here, the Yucatan Peninsula pokes out into the sea. Above the ground, jungle grows. Under the ground, 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. It soaked through soil on top of the rock. As it moved through the dirt, the water


picked up a gas called carbon dioxide. T e gas turned the water into a weak acid. T e acid nibbled away the limestone. T e acid caused a reaction, dissolving bits


and pieces of the rock. T is change is a form of weathering. It’s a process in which rocks are broken down into smaller pieces. Over millions of years, weathering carved


gaps in the rock. Rainwater dripped in. T en groundwater flowed through. Near the coast, ocean waves rushed in and out. All this moving water eroded the rock. It


carried away bits and pieces. Bit by bit, this erosion made the gaps in the rock bigger and bigger. Many gaps became caves.


UNITED STATES


Flooded! As the rainwater dripped through the rock, it did more than carve tunnels. It dissolved minerals in the rock. T e water dripped and trickled. T en some of these minerals hardened again. T ey became new rocks. T ese new rocks had new


Yucatan Peninsula


PACIFIC OCEAN


shapes. Some hung from cave ceilings like fangs. Others rose from cave floors like towers. Others looked like wrinkly rock curtains or even bells. T en, about 18,000 years ago,


Earth’s climate began to warm. Glaciers melted. Oceans rose. T e rising water flooded the caves. It hid them from sight.


12 NATIONAL GEOGRAPHIC EXPLORER


MEXICO


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