Mammoth Cave National Park
Mammoth Cave National Park is located in central Kentucky. The
park contains portions of Mammoth Cave, the longest cave system
known in the world. The official name of the system is the
Mammoth-Flint Ridge Cave System for the ridge under which the
cave has formed. The park was established as a national park on
July 1, 1941. It became a World Heritage Site in 1981, and an
international Biosphere Reserve in 1990.
The park's 52,835 acres are located primarily in Edmonson
County, Kentucky, with small areas extending eastward into Hart
County and Barren County. It is centered around the Green River,
with a tributary, the Nolin River, feeding into the Green just
inside the park. With over 390 miles of passageways it is by far
the world's longest known cave system, being well over twice as
long as the second longest cave system, which is South Dakota's
Jewel Cave with just over 150 miles of known passageways.
Mammoth Cave's Limestone labyrinth
Mammoth Cave developed in thick limestone strata capped by a
layer of sandstone, making the system remarkably stable. It is
known to include more than 390 miles 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
sandstones give rise to an epikarstic zone, in which tiny
conduits 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 St. 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 St. Genevieve Formation.
Each of the primary layers of limestone are divided further into
named geological units and subunits. 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.
Mammoth Cave Shrimp
Mammoth Cave is home to the endangered Kentucky cave shrimp, a
sightless albino shrimp.
