June 20. Mammoth Cave

Photo by Navin75, via Wikipedia, under CC-by-SA license

Mammoth Cave, Kentucky, with more than 400 miles of mapped passages and connected to the Flint Ridge cave system, is the longest known cave in the world. Dissolution of the St. Louis and St. Genevieve Limestones of Mississippian age, about 325 to 350 million years old, produced the cave. The process may have begun as much as 30 million years ago, but most of the cave’s development is less than one million years old. Mammoth Cave is a “living cave” where dissolution and precipitation of cave features by running water are still continuing today.  

The cave includes an underground river and large rooms dissolved from the limestone, but which are often partly filled by redeposited calcium carbonate, calcite, in the myriad of forms you know about in caves – stalagmites, stalactites, flowstones, and much more that give the cave its beauty.

In 1972, members of the Cave Research Foundation exploring the Flint Ridge cave system discovered the connection between those caves and Mammoth Cave, making it by far the longest cave in the world. Steve Wells, a fellow geology student with me at Indiana University, was part of the team that pushed the connection. Steve and I were teaching assistants at the Indiana University Geologic Field Station, and he went on to become the President of the Desert Research Institute in Nevada.

Mammoth Cave was a commercial resource in the early 19th century, and during the War of 1812 it was sold several times as a source of nitrates to make gunpowder. Slaves mined the ore, but when the price of saltpeter, calcium nitrate, fell after the war, it had a long history as a private tourist attraction. It didn’t become a national park until 1941.

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Francis Pettijohn was born June 20, 1904, at Waterford, Wisconsin. His work focused on sedimentology, the processes that result in sedimentary rocks.

—Richard I. Gibson

Reference: Geology of Mammoth Cave National Park by Ann Livesay, 1962 

Photo by Navin75, via Wikipedia, under CC-by-SA license