The second longest cave in the world just got a little larger—at least in terms of the number of miles of surveyed passages. Volunteer cavers have recently mapped new areas at Jewel Cave National Monument which pushed the total known length of the South Dakota cave past the 150-mile mark.

Park officials recently announced the results of recent exploration in Jewel Cave:

On February 27th, three groups of volunteer cavers from South Dakota, Colorado, Kansas, New Mexico, and Utah explored and mapped 3,032.65 feet of passages, bringing the cave’s total surveyed length to 150.12 miles. Jewel Cave remains the second longest cave in the world, following Kentucky’s Mammoth Cave, which is more than 367 miles in length.

Being the first known human to see a section of cave is an exciting idea, but it's also hard work. This is not a project for those who are inclined to ask, "Are we there yet?"—or anyone who is uncomfortablOe in tight quarters.

Due to its size and complexity, exploring Jewel Cave takes both physical and mental endurance. Experienced cavers travel long distances over slippery rocks, straddle wide crevices, climb over house-sized boulders, and worm their way through tight passages to reach areas that have not yet been explored.

During the weekend’s survey effort, one group travelled more than five hours into the southeastern portion of the cave before reaching the “leads” that they had come to the park to explore. These cavers were the first people to ever enter these areas, where they found a mixture of crawls and large passages, some of them beautifully decorated with delicate speleothems (cave formations).

After creating a detailed map of more than 1,600 feet of the cave, the group emerged on the surface after spending over 20 hours underground.

The other teams worked in the northern and central portions of the cave, in areas that had first been discovered by Herb and Jan Conn in the 1960s. One team travelled to an area near the historic entrance to the cave, spending over 12 hours underground and mapping over 1,000 feet. Yet another group worked in an area near the route used for the public Wild Caving Tours, mapping a few hundred feet in about nine hours.

“Jewel Cave is truly a significant and unique resource within the National Park System,” said acting superintendent Mike Tranel. “The complexity of the cave system makes it world class, and it continues to inspire exploration and discovery.”

President Theodore Roosevelt signed a proclamation that established Jewel Cave National Monument on February 7, 1908. It's unlikely those who supported designation of the area over a century ago could have imagined the extent of the wonders that lay underground, and there's almost certainly more new territory yet to be discovered.

A park spokesman notes,

"Caves remain one of the world’s last frontiers, and airflow studies indicate that most of Jewel Cave remains undiscovered. The monument enlists volunteer cavers to continue to learn more about its resources, and the data recorded by exploration teams provides the foundation for park planning and management."

The staff at Jewel Cave offers a variety of guided tours, both above and below ground. Tours that offer an easy sample of the developed portion of the cave are available throughout the year. During the summer months, a strenuous Spelunking Tour offers hardy and adventurous visitors the chance to don a hard hat and headlamp and sample a small section of the natural portion of the underground world.

You'll find additional information about Jewel Cave National Monument, including updates on future exploration efforts and details to help plan a visit, on the park's website.