Some seven miles of passageways, including some subterranean lakes, have been charted in Jewel Cave National Monument/NPS

How long is Jewel Cave? If you said 150 miles, you'd be wrong. That was the length measured back in 2010 when volunteers charted more than 3,000 feet of unexplored passageways beneath the surface of Jewel Cave National Monument in South Dakota. Now the total has been pushed to 180 miles thanks to another group of volunteers.

According to the National Park Service, since 1959 cavers have been actively exploring and mapping the passages of Jewel Cave. A major breakthrough last June resulted in the discovery of more seven miles of passages, and early last month four cavers spent four days and three nights at the west end of the cave, mapping more than 6,000 feet of new passages and passing the 180-mile mark.

According to a park release, they also found two subterranean lakes - where passages intersect the Madison Aquifer. They are called Hourglass Lake and Piso Mojado ("wet floor" in Spanish).

"This is a significant discovery," said Mike Wiles, the monument's chief of resource management, "because it provides a window to the aquifer. It's a great opportunity to study microbial life in a nutrient-poor environment, and to learn more about a regionally significant aquifer."

"The ongoing exploration has been conducted exclusively by volunteer cavers, hundreds of individuals who have donated tens of thousands of hours over the last 56 years," said acting-Superintendent Don Hart.

Jewel Cave National Monument has developed a comprehensive program to train trip leaders.

"We develop a strong interpersonal relationship with them that gives us complete confidence in their caving skills and resource protection values. This is essential because, after all, we are entrusting them with the discovery of new portions of the park's primary resource," said the acting superintendent.