The longest in the world has reached 400 miles.
Kentucky landmark Mammoth Cave recently added 10 miles to its explored underground length, pushing it past the 400-mile mark, the National Park Service said recently.
The expansion is thanks to several "incremental additions to many parts of the cave rather than a single major discovery," said Charles Fox, president of the Cave Research Foundation, which enlists volunteers to help explore the cave.The popular destination in south-central Kentucky attracts enthusiasts who spend thousands of hours scouring the winding underground limestone caverns. Fox said that the group has resurveyed sections of the cave to produce maps with better detail and also added previously unexplored passages.
Roger Brucker, an author who began exploring the cave in the 1950s, said the milestone is a payoff for all the explorers who have helped find new connections over the decades. Brucker, 83, said the explored length was about 40 miles when he began going underground.
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"The fun of it to me is finding that the system is connected and how it is connected," he said. "Generally, it involves crawling through water, wading through water."
The park service said Cave Research Foundation members contributed more than 10,000 hours of volunteer work at the cave and park last year. Brucker is a past president of the foundation.
Brucker said the underground expeditions are important because they add to discoveries about how water moves in underground formations. The cave systems reach into Edmonson, Hart and Warren counties.
"From an ecology point of view, it means that if you pollute one part of it, you're likely to see that pollution migrate to other parts of the cave system," he said.
The area's indigenous people ventured into the cave as far back as 2,000 to 4,000 years ago, park officials said. White settlers went into the cave in the 1790s, and for a time, it served as a source of saltpeter, an ingredient for gunpowder, including during the War of 1812.
The first tours started in 1816, and the now cave attracts about 700,000 visitors a year. Last year, Mammoth Cave National Park opened a new $16 million visitors center.