The Geology of Mammoth Cave National Park, Kentucky

Mammoth Cave National Park in south-central Kentucky protects the longest known cave system on Earth, and underground rivers at the water table are still carving new passages. This summary draws on the National Park Service's Geodiversity Atlas, which gathers what the NPS Geologic Resources Inventory knows about each park's rocks, sediments, landforms, fossils, soils and the processes that shape them.

The park

The park lies in Barren, Edmonson and Hart Counties, about 140 km (90 mi) south of Louisville and 30 km (20 mi) northeast of Bowling Green. Established on July 1, 1941, it covers about 21,379 hectares (52,830 acres). Besides the cave, it protects the Green and Nolin river valleys and evidence of human history reaching back 12,000 years. It was designated a World Heritage Site in 1981 and an International Biosphere Reserve in 1990.

A karst landscape

Mammoth Cave is one of the most studied karst areas in the world. Over millions of years, water has worked its way ever deeper into the ground, forming sinking streams, sinkholes, speleothems and a vast network of connected passages. The caves formed in limestone of Mississippian age (about 359 to 318 million years ago) to Pennsylvanian age (318 to 299 million years ago).

The park holds more than 400 caves. The Mammoth Cave System among them is, according to the park, more than twice as long as any other known cave in the world, and more passages are found every year, keeping mapping, documentation and research going.

Many animals here are adapted to life in caves, on land and in water, including three endangered species: the Kentucky cave shrimp (Palaemonias ganteri), the Indiana bat (Myotis sodalis) and the gray bat (Myotis grisescens).

Geologic Resources Inventory map. National Park Service.

Ridges, valleys and rivers

The park sits near the southeastern edge of the Chester Upland, a raised region capped by sandstone that resists erosion. The Green River meanders through the park from east to west, and the Nolin River cuts across its northwest corner, flowing south to join the Green.

South of the Green River the land forms a series of northwest-trending valleys — Woolsey, Doyle and Houchins — and ridges — Joppa, Mammoth Cave and Flint. To the southeast the park is bordered by the Chester Escarpment, a line of fairly steep cliffs that divides the Chester Upland from the Pennyroyal Plateau. The park belongs to the Interior Low Plateaus Physiographic Province.

Fossils

Fossils occur both in surface outcrops and inside the caves, in five Upper Mississippian units: the St. Louis Limestone, Ste. Genevieve Formation, Girkin Formation, Haney Limestone and Glen Dean Limestone.

• St. Louis: marine invertebrates, including corals, brachiopods, gastropods, cephalopods, crinoids, echinoderms, bryozoans and bivalves.
• Ste. Genevieve: marine invertebrates (brachiopods, echinoderms and crinoids) and vertebrates (conodonts and remains of sharks and fish).
• Girkin: brachiopods, corals, crinoids and echinoids.

Fossils in national parks are protected under the Paleontological Resources Preservation Act of 2009.

Threats to the water

Contamination of the region's karst aquifers is a long-term, continuing threat. Changes in and around the park have put many stresses on its aquatic ecosystem. Pollution from diffuse sources, such as nutrients, pesticides and sediment, and from single sources, such as toxic spills, can reach the park's waters and the wildlife that depend on them. Physical changes to the park's hydrology, actual or potential, could severely alter how water flows and the habitat it supports. Caves in national parks are protected under the Federal Cave Resources Protection Act of 1988.

Mammoth Cave's historic entrance. National Park Service.

Maps and inventories

The Geologic Resources Inventory produces digital geologic maps, reports and posters for more than 270 natural resource parks, and a Soil Resources Inventory has also been completed for Mammoth Cave. Both are available through the NPS DataStore.

Sources

• National Park Service, "NPS Geodiversity Atlas—Mammoth Cave National Park, Kentucky": https://www.nps.gov/articles/nps-geodiversity-atlas-mammoth-cave-national-park-kentucky.htm
• The source gives two different surveyed lengths for the Mammoth Cave System; this page does not state one.
• The source spells the Indiana bat's species name "sodalist"; this page uses Myotis sodalis.
• The report cover shown on the source page is not reproduced.