The World’s Longest Cave Is in Kentucky

Diana Rus

Mammoth Cave is the world's longest-known cave system with more than 420 miles of surveyed passageways. Mammoth Cave is almost twice as long as the second-longest cave system, Mexico's Sac Actun underwater cave.

Since the 1972 unification of Mammoth Cave with the even longer system under Flint Ridge to the north, the system has been known as the Mammoth-Flint Ridge Cave System.

Mammoth Cave National Park is a UNESCO World Heritage Site and International Biosphere Reserve.

About Mammoth Cave

The world’s longest-known cave, Mammoth Cave, is a well-researched example of a "solution cave".

Solution caves are created when rainfall percolates through the soil and gathers up carbon dioxide from the air and the soil, creating a weak acid. In order to create a narrow channel for the water to pass through, this acidic water squeezes between the thin limestone layers and bedrock layers.

Minerals in the limestone are actively dissolved by the water. The canals get larger over an extremely long period of time, allowing water to flow more freely. The water passages expand as more water flows through them. These tunnels are formally classified as caves once they are large enough for people to enter and explore.

The world’s longest-known cave

Researchers have found that Mammoth Cave’s rock beds to the Mississippian Period.

The rock layers at Mammoth Cave have been dated to the Mississippian Era.

About 320–360 million years ago, rock beds were developed. But it wasn't until 10 to 15 million years ago when streams and rivers running over the surface allowed water to sink in and enter the rock layers through tiny fractures, that Mammoth Cave's passages began to develop.

The highest passages formed until about 2 million years ago, when ice age activities changed the amount of water coming into the cave and the remaining cave streams dropped to lower levels of the cave, according to studies.

Mammoth Cave now has five different "levels" of tunnels. These are made up of four fossil levels and the lowest level, the modern river level, which is nearly 300 feet below the surface.

The subterranean rivers that flow out of the cave and into the Green River are still building the cave today as waterfalls through these wide and narrow passages to the water table.


The majority of the passages in Mammoth Cave are dry, with water only sometimes entering into certain sections where stalactites, stalagmites, and other formations may be found.

Visitors can see several kinds of cave passages in Mammoth Cave. Some of them are:

  • Canyon Passages
  • Large Canyon Composite Passages
  • Tube Passages
  • Vertical Shafts
  • Keyhole Passages

Mammoth Cave National Park

Mammoth Cave National Park is a national park in west-central Kentucky that includes portions of Mammoth Cave, the world's longest cave system.

The park was established on July 1, 1941, and it became a national park on October 27, 1981, a world heritage site on September 26, 1990, an international biosphere reserve on September 26, 2020, and an international dark sky park on October 28, 2021.

The park's 52,830 acres are mostly in Edmonson County, with some parts stretching east into Hart and Barren counties.

The Green River flows through the park, with a branch known as the Nolin River feeding into it immediately inside the park's borders.


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