Kentucky SuperGraphic

Mammoth Cave

With more than 348 miles of surveyed passage, Mammoth Cave is easily the longest cave known in the world. It's grand passages, locally known as "avenues", are laid out in such neat grids that you might imagine they were the design of a city architect. Level passages, however, are occasionally punctuated by towering dome pits, where aggressive waters have invaded the cave from the surface. At the lowest reaches of the cave, the River Styx and Echo River wend their way toward surface springs, giving a glimpse of cave development in action.Mammoth Cave has at least five known levels of interconnecting passageways. Each of these levels has it's own complex system of avenues. The way in which these levels formed allowed each level to connect to the level above and the level below. As the water dropped through these levels, the passageway above became dry.

Currently, the fifth level of the cave is still being worked on by the Echo River - 360 feet below the surface!

The River Styx and Echo River are home to some of the most unusual life inhabiting Mammoth Cave, including blind and unpigmented fish and crayfish. In dry passages, cave-adapted crickets, beetles and spiders take up residence.

And as you enter the grand Historic Entrance of Mammoth Cave, you follow in the footsteps of human visitors that have traversed the cave for some 4,000 years. Native Americans first made far-reaching forays into the cave by torchlight, in search of gypsum and other crystals.

How Mammoth Cave was formed

In simplified terms, Mammoth Cave was formed from the four things that are necessary for cave formation: water, rocks with cracks in them, rock-like limestone that can dissolve and an outlet from which the water can drain and leave the cave dry.

The process of forming caves in soluble rock is very slow. It took 250 million years for Mammoth Cave to develop. Two hundred and fifty million years ago the area was covered by a shallow inland sea. For millions of years animals lived and died in the sea, their shells and bones settled in layers of slimy ooze on the sea bottom. Sand and mud washed into the sea, and they settled in layers too. Over the millenia, the layers became so thick that their weight squeezed out the water. The shells and ooze became limestone. The mud became shale and sand turned into sandstone.

In the ages that followed, the sea dried up and refilled many times. Forces within the earth caused the land to rise very slowly and the sea disappeared. The uplift tilted the rocks, and they cracked, warped and bent. Heavy rains fell and for 30 million years the Green River slowly wore its way down through sandstone to the limestone layers.

As rain falls through the atmosphere, it absorbs a small amount of carbon dioxide. It gathers additional carbon dioxide as it moves through the soil. Water mixed with carbon dioxide is a weak carbonic acid solution. As this solution of water and carbon dioxide seeps through the cracks and crevices, it dissolves the soluble rock and forms cavities and channels as it moves downward and laterally. After thousands of years of solution, underground rooms and chambers are formed.

The same process occurred with the Green River. As the water flowed over the land, it picked up acid from decaying plants. Following underground cracks, the slightly acidic water dissolved the limestone and carried it away in liquid form. This cut passages through the limestone. Water continued to flow, making the openings bigger and bigger.

Mammoth Cave has at least five known levels of interconnecting passageways. Each of these levels has it's own complex system of avenues. The way in which these levels formed allowed each level to connect to the level above and the level below. As the water dropped through these levels, the passageway above became dry.