Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/708006
Bill Langer is a consulting research geologist who spent 41 years with the U.S. Geological Survey before starting his own business. He can be reached at Bill_Langer@hotmail.com CARVED IN STONE 44 AGGREGATES MANAGER / July 2016 M y wife, Pam; grandkids, Donovan and Delaney; and I spent spring break camping in southern Arizona around Tucson. The highlight of the trip was our visit to a world-class geologic wonder Kartchner Caverns State Park. The obvious draw to the park is Kartchner Caverns and its intricate formations, called "speleothems." Kartchner Caverns is considered a "living cave" because its speleotherms are still growing, and new speleotherms continue to be formed. Rainwater, combined with carbon dioxide from the atmosphere and decaying veg- etation, forms carbonic acid that percolates through fractures in the surrounding limestone. The acid dissolves rock, creating openings. Over geologic time, these openings enlarged, forming Kartchner Caverns with its ceilings and floors orna- mented with speleotherms, such as stalactites hanging from the ceiling (where they hang on tight) and stalagmites on the floor (where you might trip on them). There are two 90-minute guided tours through the caverns. The Throne-Ro- tunda tour has grand vistas overlooking the cave formations. The tour through the Big Room offers visitors an up-close look at the formations. We went on both tours; both were fantastic. We saw one the world's largest soda straws (in the Throne Room), bacon, 'tur- nip' shields (Big Room), totems, waterfalls, columns, helictites, fried eggs, cave coral, popcorn, draperies, 'birds nest' needle quartz formations (Big Room), straw- berry flowstone, and the world's most extensive formation of brushite moonmilk (Big Room). The shape of a speleotherm depends on whether the water is seeping, drip- ping, or flowing and whether the water is under pressure or not. Seeping water forms shields. Fast dripping water forms stalagmites. Slowly dripping water forms stalactites and soda straws. Water flowing along fractures forms waterfalls or flowstones. Water under pressure forms helictites, which are stalactities that defy gravity by branching out in various directions. Calcite that forms speleotherms is naturally white. However, it can be colored by other minerals in the water – red from iron oxide (rust), blue or black from manganese, and brown or tan from organic matter. The speleotherms were formed over the past 200,000 years; many have been continuously growing for tens of thousands of years. A soda straw, for example, grows just 1/64th of an inch in a year, and a cubic inch of calcite takes a century to form. In addition to a place of beauty, the Big Room is a cave bat maternity ward. There is black grime on the ceiling where the bats hang and piles of guano line the floor. There even is a bat's body entombed in one of the cave's formations. Bats do not occupy the Throne Room. When the guide asked if anyone knew why, Delaney (11 years old) popped up, "Be- cause they don't have food." "Right!" a somewhat surprised guide replied. When I asked Delaney how she knew the answer she said, "It's common knowledge. You need food, water, and shelter to live. There is plenty of water, and the cave provides shelter, so the only thing missing is food." Common knowledge, indeed. Kartchner Caverns is one of the top 10 living caves in the world and was voted the best cave in America (2016 USA Today 10 Best Readers' Choice Awards). But the geology is only half the story. How the caverns were discovered and developed is a story in itself. More about that next month. Speleotherms, such as stalactites and stalagmites, continue to grow in this living cave. Kartchner Caverns: A World-Class Geologic Wonder Kubla Kahn is a 58-foot tall column. Notice person for scale. Photo copyright Arizona State Parks.