John Bordsen

Special to USA TODAY

TOWNSEND, Tenn. — Near the end of a string of two-lane roads about 30 minutes south of Dollywood, the Hatfield & McCoy Dinner Show and the Titanic Museum, is the largest and most organic attraction in the Pigeon Forge/Gatlinburg area.

Though under the radar for most tourists — only a half-dozen billboards tout Tuckaleechee Caverns — the family-owned site thrives on a word-of-mouth clientele and praise from TripAdvisor and AAA.

It’s also an unlikely player in the global geopolitical conflict over North Korea: In an enormous chamber 350 feet down, sharp-eyed tourists can see sophisticated seismic equipment that tracks earthquakes and underground nuclear tests — with data going to the United Nations and available to the U.S. Department of Defense.

And up in the visitor center, a real-time monitor shows what’s rumbling within planet Earth — and where.

Family-owned underground maze

The caverns, estimated to be at least 20 million to 30 million years old, are one of the newer major subterranean finds in Tennessee. In the early 1930s, 6-year-old Bill Vananda and a friend were poking around a rural sinkhole and found a 4-foot opening that led to a network of caves.

Loggers working the western side of the Great Smoky Mountains in the 1850s named this remote area Dry Valley: Trees were plentiful, but streams were few. It was assumed that a sizable drainage system existed underground.

What his grandfather unearthed, says Benjamin Vananda, was one of the largest unexplored cave systems in the eastern United States. Vananda, 37, currently manages the attraction.

“Our family early-on bought the 200 acres around the sinkhole, as well as mineral rights — ownership of what’s below,” he says. “How far does it go? I actually don’t know. I think maybe 10% of it has been explored, and on tours you see only about 6% of that.

“There are literally millions of rooms.”

A visitor center now covers the vastly expanded sinkhole opening. Concrete steps and walkways descend into water-carved corridors and rooms of limestone studded with calcium carbonate deposits left by water drips.

Underground streams often parallel man-made walkways. The guided tour covers 1½ miles. Along the way is a two-tier subterranean waterfall.

Follow the water

Flowing water is key to determining how extensive the Tuckaleechee system might be. Geologists placed tracer dyes in the underground rivers and learned the cavern aquifer extends 4 miles east to White Oak Sinks, in the isolated valley of Cades Cove in Great Smoky Mountains National Park near the North Carolina line.

You may have to duck now and again to clear ceilings along pathways of the guided tour, which is not handicap accessible. Photography is allowed throughout but is difficult: Floor-level electric lighting is subdued, with illumination diffused by metal shades. These are “living” caverns, with bats sleeping in crannies here and there.

This is not a hard-hat affair — some passages could accommodate golf carts — but the route can be disorienting. Fresh air and running water overwhelm any sense of depth. You’re actually hundreds of feet underground.

“The air temperature is a constant 58 degrees year-round, and that’s determined by our distance from the equator and area elevation of 1,200 feet,” Benjamin Vananda says. “The water temperature is about 52 degrees and has been tested at 98.9% pure; the residual is calcium carbonate with some traces of iron. Calcium carbonate is what you find in Tums.”

Like his father, Steven (the guy with the gray-streaked beard behind the counter upstairs), Benjamin pretty much grew up in the underground maze: “I’ve explored more of it than anyone; I’ve been to places down there no (other) human has been.”

Benjamin, 6 feet 2 inches tall, knows where to duck. He is a member of the National Caves Association and National Speleological Society. He darts on and off the walkways like a sure-footed goat, pulling out his flashlight — as do the guides he trains — to point out formations created by millions of years of mineral-water drip: icicle-looking stalactites, stalagmites that accumulate from the cavern floor, pillars that form when the two merge. There are wall-clinging popcorn, cave flower, box and “rope” formations created from specialized drips. He says one of the chandelier formations — delicate-looking fixtures caused by eons of water spewing through tiny holes like primeval fire sprinklers — could be the largest in the world.

The major “wow” is the Big Room, where tourists approaching from the other side of the subterranean canyon appear to be the size of ants. That chamber is 400 feet by 300 feet and 150 feet from floor to ceiling. Without a horizon, strong lighting or other typical reference points, its enormity is hard to fathom. A yodel goes a long way into a dim nowhere, and parts of the floor descend an additional 150 feet. The Big Room could hold a 15-story building, and it is the deepest point open to the public. Its bottom is 500 to 600 feet under Little Mountain.

In a different passage on the tour, a quarter-mile away, guides may point out a dark and distant recessed ledge where it looks like workers left a 42-inch Sears Craftsman tool cabinet and some other metal boxes. That’s government stuff.

Listening to the rumble

The Vanandas opened Tuckaleechee Caverns in 1953, about the time an area performer named Dolly Parton was learning her craft. The Big Room was discovered two years later. And when the 1962 Cuban Missile Crisis came along, the government installed its first seismic measuring equipment deep underground. Owner Bill Vananda gave them no-charge permission.

When grandson Benjamin Vananda came home after working in IT for a corporation in Marysville, Tenn., he began assisting with the care and feeding of the cavern’s seismographic station.

Blue conduits connect the devices to a surface-level satellite dish that sends encrypted data to the U.N.’s Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna, Austria.

Another line goes to the doorway of the visitor center, where a cabinet the size of a Redbox DVD kiosk — but with a microwave-size screen at eye level — displays a live- map showing where rumbles are taking place.

There are other seismic collection sites across North America, but Tuckaleechee is one of the few in eastern North America that monitors nuclear test explosions. It can be used in combination with sites worldwide to triangulate incidents to within millimeters, Vananda says.

Richard Williams, adjunct associate professor of geophysics at the University of Tennessee, has been working with Tuckaleechee for three decades. “In the early 1970s,” he says, “the Nuclear Regulatory Agency became interested in monitoring earthquakes in eastern Tennessee. They were interested in the safety of the nuclear reactors at Oak Ridge.”

Williams, a seismologist, explains why Tuckaleechee is prime for delicate monitoring: “A lot of noise recorded is simply wind, so if we can put a sensor underground that’s good — the farther the better. And unlike putting a sensor in a hole and cementing it into the ground, here we can more easily check on it and make repairs.”

In the visitor center, Benjamin Vananda unlocks the monitor cabinet to check the printer paper. Is the government OK with this?

Vananda looks over his shoulder at a discreetly mounted ceiling camera. “While we’re watching this, they’re watching us watching them.”

Some printouts of notable seismic incidents are posted just around the corner — polygraph-style printouts of earthquakes in Asia and California; an underground nuclear test in North Korea.

They hang just above a rack displaying M&Ms, Butterfinger candy bars, Blow Pops and beef jerky.

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