Mammoth Cave National Park is a national park in south-central Kentucky, encompassing portions of Mammoth Cave, the longest cave system known in the world. The park's are located primarily in Edmonson County, with small areas extending eastward into Hart and Barren counties. The Green River runs through the park, with a tributary called the Nolin River feeding into the Green just inside the park.
The cave system has formally been known as the Mammoth–Flint Ridge Cave System since 1972, when a connection was discovered between Mammoth Cave and the even-longer system under Flint Ridge to the north. As of 2022, more than of passageways had been surveyed, over 1.5 times longer than the second-longest cave system, Mexico's Sac Actun underwater cave.
The park was established as a national park on July 1, 1941, after oft-contentious eminent-domain proceedings whose consequences still affect the region. It was named a World Heritage Site on October 27, 1981; an international Biosphere Reserve on September 26, 1990; and an International Dark Sky Park on October 28, 2021.
Park purpose
As stated in the foundation document:
Geology
Mammoth Cave developed in thick Mississippian-aged limestone strata capped by a layer of sandstone, which has made the system remarkably stable. It is known to include more than of passageway. New discoveries and connections add several miles to this figure each year. Mammoth Cave National Park was established to preserve the cave system.
The upper sandstone member is known as the Big Clifty Sandstone. Thin, sparse layers of limestone interspersed within the sandstone give rise to an epikarstic zone, in which tiny conduits (cave passages too small to enter) are dissolved by the natural acidity of groundwater. The epikarstic zone concentrates local flows of runoff into high-elevation springs which emerge at the edges of ridges. The resurgent water from these springs typically flows briefly on the surface before sinking underground again at elevation of the contact between the sandstone caprock and the underlying massive limestones. It is in these underlying massive limestone layers that the human-explorable caves of the region have naturally developed.
The limestone layers of the stratigraphic column beneath the Big Clifty, in increasing order of depth below the ridgetops, are the Girkin Formation, the Ste. Genevieve Limestone, and the St. Louis Limestone. For example, the large Main Cave passage seen on the Historic Tour is located at the bottom of the Girkin and the top of the Ste. Genevieve Formation.
Each of the primary layers of limestone is divided further into named geological units and sub-units. One area of cave research involves correlating the stratigraphy with the cave survey produced by explorers. This makes it possible to produce approximate three-dimensional maps of the contours of the various layer boundaries without the necessity for test wells and extracting core samples.
The upper sandstone caprock is relatively hard for water to penetrate: the exceptions are where vertical cracks occur. This protective role means that many of the older, upper passages of the cave system are very dry, with no stalactites, stalagmites, or other formations which require flowing or dripping water to develop.
However, the sandstone caprock layer has been dissolved and eroded at many locations within the park, such as the Frozen Niagara room. The contact between limestone and sandstone can be found by hiking from the valley bottoms to the ridgetops: typically, as one approaches the top of a ridge, one sees the outcrops of exposed rock change in composition from limestone to sandstone at a well-defined elevation.
At one valley bottom in the southern region of the park, a massive sinkhole has developed. Known as Cedar Sink, the sinkhole features a small river entering one side and disappearing back underground at the other side.
Visiting
The National Park Service offers several cave tours to visitors. Some notable features of the cave, such as Grand Avenue, Frozen Niagara, and Fat Man's Misery, can be seen on lighted tours ranging from one to six hours in length. Two tours, lit only by visitor-carried paraffin lamps, are popular alternatives to the electric-lit routes. Several "wild" tours venture away from the developed parts of the cave into muddy crawls and dusty tunnels.
The Echo River Tour, one of the cave's most famous attractions, took visitors on a boat ride along an underground river. The tour was discontinued for logistic and environmental reasons in the early 1990s.