Dixie Caverns

exploring a wild cave

examining calcite speleothems

It's a long trip back to the GMU Fairfax Campus from Southwestern Virginia, so we'll stop on the way. We'll get "grounded" one last time in geology, by exploring Dixie Caverns. By now, you'll remember that limestone is calcium carbonate (CaCO₃), and dolomite has magnesium in it (CaMg(CO₃)₂).

Dixie Caverns is one of Virginia's commercial show caves. There are over 4,000 "wild" caves in Virginia, according to the Virginia Speleological Survey, but only about a ten commercial show caves. Dixie Caverns was heavily damaged by tourists who broke off formations as souveniers, but still shows the geological processes of cave formation and, ultimately, how "breakdown" leads to the natural destruction of caves.

Caves are a unique habitat. There is no light, so expect to find animals but not plants in a cave. The food chain for animals that live exclusively in a cave is based on the little bit of detritus that washes in, or on the animals that feed outside the cave. Bats can create great mounds of guano underneath their roosting sites, and various forms of life from bacteria to cave crickets can live on the energy provided by that food source. Most commercial cave tours involve walking along a paved trail, looking at formations illuminated with lights hidden behind rocks or rock-colored shades. If the lights are left on regularly, then algae spores can germinate and grow on the cave formations in the moist environment. The chlorophyll used by the algae to photosynthesize food adds an unnatural green color and texture to the cave formations.

Caves are usually very moist environments. Salamanders, fish, and insects are protected against predators in a cave, making them an attractive niche. Obligate cave dwellers are those animals that have evolved to the point where they are no longer able to survive outside the cave, often because they have become blind. (Why waste energy growing and maintaining eyes, when a cave is always pitch black?)

Caves also provide a steady temperature, reflecting the average temperature of the area. Only near the entrance of a cave will the temperature change between day and night, and with the seasons. Virginia caves are about 54-56 degrees, every day, every hour. (The one commercial cave in North Carolina, Linville Caverns, is always 52 degrees - it's higher in the mountains, so its average temperature is cooler even though it's further south.)

Caves are not always a static environment; they can change dramatically at times. A summer thunderstorm can result in a rush of water into a cave, importing leaf debris, raising the temperature, and even drowning bats and breaking cave formations if the cave fllods completely. (WARNING: cavers can also be caught... and drowned. Beware of entering wild caves if rainstorms are likely in the area. While you're underground, you won't hear the thunder and know when to head back.)

Thomas Jefferson understood that caves, groundwater, and springs were related, but he lacked a fundamental understanding of how caves were formed by water. Referring to Madison's Cave, which is now a commercial cave called Grand Caverns, he understood that the waters of the Shenandoah River had not carved out the hole undeground via wave action... so he got that part right.. He said¹ that passages terminated in:

“basons [sic] of water of unknown extent, and which I should judge to be nearly on a level with the water of the river; however, I do not think they are formed by refluent water from that, because they are never turbid; because they do not rise and fall in correspondence with that in times of flood, or of drought; and because the water is always cool. It is probably one of the many reservoirs with which the interior parts of the earth are supposed to abound, and which yield supplies to the fountains of water, distinguished from others only by its being accessible.

Questions to consider:

- how do places like "Dixie Caverns" get their names... and just who was Dixie?

- does Dixie Caverns need greater protection from potential damage to the natural resources? If so, how should that protection be provided?

- should tourists be allowed to see Dixie Taverns without guided tours?

- in what ways is Dixie Caverns different from Natural Bridge, geologically and economically?

- how would tourism at Dixie Caverns be affected by making I-81 into a toll road, or building I-73?

- if you were to write the text for a historical marker at Dixie Taverns, what would you say?

- where are the bats?

- where is the water carving out the cave now? is the cave still "living"?

- why was there a Superfund site near Dixie Caverns? what was dangerous about the waste depsited there? what is the current status of that site?

- if global warming happens in your lifetime, how will Dixie Caverns change?

- how old is a cave? is it the age of the rock, or the age of the hole in the rock? how do we date the age of the hole?

• Ground Water, Caves, and Temperature
• Dixie Caverns
• Environmental Protection Agency
• Dixie Caverns County Landfill
• Virginia Cave Board - Ten Questions About Caves and the Virginia Cave Board
• Virginia Speleological Survey
• Virginia Tourism Corporation - Virgina's Caverns

References