In observance of National Groundwater Awareness Week last week, this edition of GeoLifestyle will explore caverns—marvels formed by the groundwater processes of dissolution and precipitation. Although caverns can be found all over the world, I’ve recently visited these two here in the United States.
Sharon Lyon
Editor, GeoLifestyle
Luray Caverns, Virginia
Belikova Oksana/ Shutterstock.com
Billed as “Geology’s Hall of Fame,” Luray Caverns is located in the Shenandoah Valley of Virginia.
Luray is known for its grand rooms decorated with massive karst features—stalactites, stalagmites, columns, flowstone, and draperies. Several stalactites in Luray’s Giant’s Hall column are more than 50 feet long. The cave’s underground pools trick your eye with their reflections that make stalactites appear to be mirror-image stalagmites.
Geological facts:
Luray Caverns formed within the Ordovician-age Beekmantown Dolomite, which was deposited as part of an early-Paleozoic carbonate bank.
The cavern contains myriad colors—white speleothems are pure calcium carbonate; reds and yellows are due to iron; black is from manganese dioxide, and blues and greens are from copper compounds.
Formations have fun names such as Saracen’s Tent, Titania’s Veil, the Wishing Well, Totem Poles, and Fried Eggs.
Calcium carbonate precipitation is ongoing at Luray, although it is a slow process, so the speleothems are still “growing.”
Cave history:
In 1878, three men felt a cool breeze coming from a sinkhole. After four hours of digging, they slid down a rope with candles in hand, and they discovered Luray Caverns. The cavern opened to tourists in 1880.
In 1887, 13 arc lights were installed in the cave, powered by an engine-driven generator roughly seven miles away. This was the first instance on record of a cave lighted by electricity.
In 1901, a sanatorium built on the property became the first “air-conditioned” building in America. Workers connected a shaft into the caverns, allowing cool underground air to fill the rooms.
In 1954, the Great Stalacpipe Organ was installed in the cavern. The organ contains strikers which tap stalactites of different sizes to produce different tones. Organ concerts are still held. Take a listenhere.
In 1974, Luray Caverns was designated a Registered Natural National Landmark.
The temperature in the caverns is uniformly 54o F, so bring a sweater.
In addition to the caverns, the property houses the Car and Carriage Caravan Museum, Luray Valley Museum & Shenandoah Heritage Village, Toy Town Junction, Gem Sluice, Garden Maze, and Rope Adventure Park.
The bottom line: Luray Caverns is hands-down the most beautiful cavern I’ve ever toured, with its stunning array of speleothems. It is well worth the price of admission and is a (long) day trip from Washington, D.C.
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Located about 17 miles east of Tucson, Colossal Cave is on the west side of the Rincon Mountains. We took the cave tour on our recent trip to the Tucson Gem & Mineral Show.
Geology of the cave:
The Rincon Mountains formed as a metamorphic core complex, a gneissic dome covered with stretched metamorphic rocks.
As the core pushed upward, thin wedges of overlying Paleozoic sedimentary rocks became detached and were dragged and broken.
Colossal Cave formed in the Mississippian-age Escabrosa Limestone, one of these detached blocks.
The dissolution of the cave probably occurred in the early Pliocene as groundwater seeped through joints in the limestone.
After the solution of the cave, the groundwater drained away. Rainwater trickled through the overlying limestone, precipitating stalactites, stalagmites, and flowstone.
At the end of the Pleistocene, with increasing aridity, Colossal Cave became a dry cave, with no water flow, so its formations no longer ‘grow.’
Cave history:
Artifacts within the cave indicate that the Hohokam—early Native Americans—used the cave as temporary shelter as early as 900 A.D.
The cave was rediscovered in 1879 and became legendary when train robbers used it as a hideout.
In 1905, a tunnel was excavated to mine bat guano, which was shipped to Los Angeles for fertilizer.
During the Great Depression, the Civilian Conservation Corps built the park roads and walkways inside the cave. They also created the stone building at the cave.
Today, Colossal Cave Mountain Park includes two other caves, Arkenstone and La Tetera, which are protected and not open to the public.
Fun fact: Sesame Street filmed a special at Colossal Cave. Big Bird follows a treasure map to find his Great Granny’s treasure chest. There’s even a Big Bird-shaped hole in one of the cave walls!
The Classic Cave Tour is a half-mile, 40-minute walk with 365 stairs. We opted for this tour.
The Ladder Tour lets you climb ladders, squeeze through narrow passages, and cross rock bridges for 1.5 hours.
The Wild Cave Tour is a 3-hour crawl-and-climb through narrow, unlit, unmarked passageways, with hard hats and lights, gloves, knee and elbow pads. It is only for the non-claustrophobic.
The bottom line: The history and geology are what make the tour worthwhile and interesting. The views inside the cave itself are not the most beautiful I’ve ever seen, as many of the stalactites were broken and taken as souvenirs by early tourists.
Drip by Drip…
Polished piece of stalactite, Courtesy of Sharon Lyon
Calcite precipitation is a slow process. Can you guess how long it took for one inch of stalactite to form at Luray Caverns?
a. 10–30 years
b. 100–300 years
c. 1000–3000 years
See the answer next week!
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