Russell Cave National Monument - Geology

Geology

The rock from which Russell Cave was carved was formed over 300 million years ago at the bottom of an inland sea covering the region. Due to continental drift, the area that is now northeast Alabama was located very close to the Equator at the time this limestone was forming. This area is now located in a temperate climate, but 300 million years ago it was a shallow, tropical sea. Carbonaceous deposits of skeletons and shells were slowly transformed into limestone. Rainwater, mildly acidic from atmospheric carbon dioxide, slowly dissolved a portion of the limestone rock result in the formation of the cave. About 9,000 to 12,000 years ago, the collapse of a cavern roof beneath a hillside near Doran's Cove created a sinkhole and exposed Russell Cave.

Until shortly before the first occupation by Native Americans, the cavern was uninhabitable due to the presence of a large stream which occupied the entirety of the cavern. A fortuitous rockfall from the cavern roof diverted the stream to one side, however, exposing a portion of the cave floor. The first occupants dwelled on this irregular floor of rock slabs. Debris from occupants and deposits falling from the ceiling slowly raised the floor. The floor ultimately was raised an additional seven to eight feet (2.0 to 2.5 m) and up to 30 feet (9.0 m) near the upper entrance. In the 1960s, the United States Bureau of Mines installed bolts with a length of 15 feet (4.5 m) to prevent additional collapses of limestone rock.

The cave mouth faces to the east preventing the ingress of a cold north and northwest winds and allowing in the morning sun. According to a published cave map, the cave has five entrances in addition to the Main Entrance. Three of the entrances are referred to as Canoe Entrances while the other two are named the Picnic Entrance and Pig Entrance.

A natural spring flows into the cave and travels underground for 1.5 miles (2.5 km) before joining Widow's Creek and, ultimately, the Tennessee River.