The Longest Cave System In The World Is Right In Kentucky

Caves have a multifaceted allure. While the general public is drawn to them for the otherworldly atmosphere and sense of exploration, researchers take interest for the scientific value. As far as topographers know, the largest karst landscape (a type of topography that results from bedrock dissolving into caves, sinkholes, underground springs, and other characteristics beneath your feet) in the world is Mammoth Cave in Kentucky.

Listed as an UNESCO World Heritage site in 1981, Mammoth Cave National Park was established in 1941 to preserve the namesake cave system. At the time, explorers had only mapped about 40 miles of passageways. Now, more than 400 miles of pathways have been discovered beneath the hilly woodlands of Kentucky's Barren, Edmonson, and Hart Counties, and explorers have yet to find an end.

Mammoth Cave is known as a solution cave that started forming about 10 to 15 million years ago. A solution cave like this one forms when rainwater turns into a weak acid by collecting carbon dioxide as it drips through soil. As the acidic water seeps through the bedrock — limestone in this case — it eats away at the rock, creating a channel that grows over time. The passages become caves when they get big enough for people to explore them.

In Mammoth Cave, the passages closest to the surface formed about 2 million years ago when the ice age stalled the progression. However, the water continued to seep farther down, creating the lower levels of the cave. The first four levels are fossil levels, while the lowest level is more than 300 feet below the surface and called the modern river level. On tours of Mammoth Cave, guests can view the various canyon, large canyon composite, keyhole, tube, and vertical shaft passages.

Humans have known about Mammoth Cave since at least 5000 to 2000 B.C. when Native Americans became its first explorers. They mined about 16 miles of the cave for minerals — such as epsomite, gypsum, mirabilite, and selenite — and left behind artifacts, such as torches made out of cane reeds. However, legend has it that John Houchin was the first European settler to discover the cave in the early 1790s. Since it was a natural place to find saltpeter, the key ingredient in gunpowder, the cave was mined by enslaved workers before and during the War of 1812.

After the saltpeter mining stopped, Mammoth Cave became famous with the release of businessman and wealthy landowner Nahum Ward's 1815 cave map, which included a description of the system and a Native American mummy. In 1834, religious services were held in the passageways, and in 1838, enslaved explorer Stephen Bishop and a couple of other enslaved persons began offering guided tours, which continue to support the tourism industry. He became renowned for discovering many miles of the underground labyrinth and crossing the Bottomless Pit, which was believed to be impassable. Additionally, Mammoth Cave was used from 1842 to 1843 as housing for the tuberculosis patients of then owner Dr. Croghan, and remnants of the stone buildings still remain.

Explorers have uncovered loads of rocks, crystals, and geological formations throughout Mammoth Cave's passages. Since the bedrock through which the cave formed is made of limestone, that's the most common rock type, and it formed around 330 million years ago. Another prominent rock is dolomite, which looks like limestone but forms when water containing high concentrations of magnesium seeps through limestone. Also, the light gray, gritty rock located in recessed limestone ledges is siltstone, which is made of tiny quartz sediments. One of the most interesting rocks, though, may be chert or flint, which looks like blackish gray nodules sticking out of the limestone because it doesn't dissolve in the acidic water like the bedrock.

Like in many other caves, Mammoth Cave is home to stalagmites rising from the passage floors, stalactites hanging from the ceiling, and columns where the stalagmites and stalactites meet. There are many calcite and gypsum formations as well, forming over thousands of years. The calcite formations took many forms because of the different ways that water flowed through the cave. Flowstone presents as calcium carbonate curtain-like sheets along the ledges and walls, while cave popcorn are lumps of calcite that resemble grapes, peas, or (of course) popcorn. In addition, the mineral gypsum is a white crystal that takes the forms of crusts, flowers, and snowballs. It takes dry conditions for these crystals to form in caves.

Since limestone is made from sediments and fossil fragments cemented together with calcium carbonate during the Paleozoic Era, researchers have found preserved brachiopods, corals, crinoids, gastropods, and even sharks from the Mississippian Period in the bedrock. Even animals from the Cenozoic Era — such as an extinct armadillo, a mastodon, a sabre-toothed cat, and an extinct vampire bat — have been preserved as fossils.

Along with an abundance of geological marvels, Mammoth Cave is home to an ecosystem filled with wildlife. The most notable animal living in the caves is the Kentucky cave shrimp, an endangered species that is rare and can't be found anywhere else in the world. Its habitat consists of accessible and inaccessible flooded passages. This albino shrimp doesn't have eyes, and it smells, touches, and tastes its food with two sets of antennules. Since biologists couldn't find any specimens in the late 1960s and early '70s, the species' population has seemingly improved.

The aquatic ecosystem in Mammoth Cave's lower levels also includes crayfish, eyeless fish, snails, isopods, and other invertebrates that feed on rock-growing microbes. Near spring outlets, back-flood waters can wash in surface fish, some of which can get trapped and become food for the crayfish after they die and sink to the bottom. The river passageways are home to insects, too, which are ideal food for cave-dwelling bats.

On top of that, Mammoth Cave has a type of terrestrial ecosystem in which insects and animals come and go to feed, hibernate, and mate. For instance, cave crickets lay eggs in dry passages, and blind cave beetles living there feed on them. Researchers have seen birds nesting with broods in rock ledges at cave entrances, while raccoons may enter the cave to prey on bats in hibernation. Cave salamanders and orb weaver spiders come and go from the passages as well, feeding on the crickets.