Lechuguilla Cave

Stand still for a moment and listen. The Chihuahuan Desert wind moves through creosote and spiny agave. Somewhere a rock wren calls. The ground under your feet is pale, broken limestone, warm in the sun. Nothing on the surface tells you what lies below. Beneath this dry hillside runs one of the longest and deepest caves on Earth.

This is Lechuguilla Cave, inside Carlsbad Caverns National Park in southeastern New Mexico. The name sounds like this: lech-oo-GEE-ya. It comes from a desert plant, the lechuguilla agave, which grows across these slopes. Its long, stiff leaves end in sharp tips. The cave takes its name from the canyon where its entrance sits, and the canyon takes its name from the plant.

One honest point first. You cannot walk into Lechuguilla. The cave is closed to the public, and it will very likely stay that way. Only small teams of scientists, surveyors and specialist cavers enter it, and they need special permits. The entrance is sealed behind a gate. So this guide is not a tour of passages you will see today. It is a guide to the world under your feet.

For a long time, people thought this was a small and unimportant hole. In the early twentieth century, miners dug bat guano from the entrance pit. Guano is the droppings of bats, and it was valuable as fertiliser. The pit was dusty and shallow. Cavers who visited later noticed something strange, though. Wind roared up from the rubble on the floor. Moving air like that often means a large space lies beyond.

In 1986, a group of cavers received permission to dig. They removed the rubble, bucket by bucket, and finally broke through into open passage. What followed is one of the great stories of modern exploration. Year after year, survey teams pushed deeper and farther. The mapped length grew past one hundred miles, and then well beyond. Today it measures more than 150 miles, and the survey is still not finished.

The cave is also very deep. Its lowest known point lies more than four hundred and fifty metres below the entrance. That makes it one of the deepest caves in the United States. Picture a skyscraper of more than one hundred floors, turned upside down, and buried in the hill. Explorers sometimes stay underground for days at a time. They camp in the darkness and carry everything in and out.

Here is the first surprise. Most caves form when rainwater, made slightly acidic by carbon dioxide, slowly dissolves limestone from above. Lechuguilla formed in a different way — from below. Hydrogen sulfide gas rose from deep oil and gas deposits in the region. It met oxygen-rich groundwater and created sulfuric acid. That strong acid ate out the rock from the inside. Scientists now believe Carlsbad Caverns formed in a similar way.

The rock itself is ancient. These mountains are the Guadalupe Mountains, and their limestone formed as a reef in a warm, shallow sea during the Permian period, more than two hundred and fifty million years ago. Sponges, algae and shelled creatures built that reef. Later the sea dried up, the land rose, and the reef became the hills you see around you. The cave is hollowed out of that fossil reef.

The acid left behind something beautiful. When sulfuric acid reacts with limestone, it produces gypsum, a soft white mineral. In Lechuguilla, gypsum grows into enormous crystal chandeliers. Some hang several metres long from the ceiling, like frozen white fireworks. One famous room is called the Chandelier Ballroom. Explorers also found aragonite bushes, delicate mineral balloons, cave pearls, and rust-coloured formations that look like hanging icicles of iron.

The second surprise is about life. Lechuguilla has been sealed from the surface for a very long time, so it holds microbes that live in total darkness. Some feed on minerals in the rock rather than on sunlight. Scientists study them for two reasons. Some of these microbes resist antibiotics, even though they never met modern medicine. That helps researchers understand how resistance develops. Others interest space scientists, who wonder how life might survive underground on other worlds, such as Mars.

This fragile world is why the cave stays closed. A single footprint off the marked route can last for thousands of years. Skin cells, lint, and even breath can change the delicate mineral growth. Survey teams follow strict rules. They stay on flagged paths, and they carry out all of their waste. The cave also tells a story of danger. In 1991, a caver broke her leg deep inside, and her rescue took several days of careful work.

Carlsbad Caverns National Park is a World Heritage Site, protected for both its caves and its fossil reef. Lechuguilla is a large part of that importance. If you want to feel some of this underground world yourself, visit the main cavern of the park. There you can walk through great chambers formed by the same acid, and you can see gypsum, stalactites and still pools with your own eyes.

Now look around you once more. The agave leaves catch the light. The limestone is pale and rough. Somewhere below your boots, in perfect darkness, crystals keep growing, one thin layer at a time. Nobody will see most of them. As you walk away, listen for the wind in the canyon... and remember that the earth here breathes, too, through a small hole in a dry desert hill.