New Theory on How Carlsbad Cave Formed

The Big Room at Carlsbad Caverns with its gypsum formations and its huge space--bigger than six football fields and as tall as a 30-story building--inspires awe for 500,000 annual visitors, but it’s been a nagging puzzle for geologists. For decades, visitors were told the cave was formed by the relentless drip-drip-drip of carbonic acid eating away at the limestone. But where did all that rock go?

In most caves formed that way, subterranean streams carry off the residue. There were no underground streams in Carlsbad Caverns. The story scientists had been telling the tourists didn’t make sense to geologist Carol Hill of the University of New Mexico.

UNM biologist Diana Northup, who worked with Hill, said single-cell microbes--bacteria--that fed on pools of petroleum under the Carlsbad region were the real cave carvers. “The carbon compounds available in oil are eaten by the microorganisms,” Northup said, “and the product they produce is hydrogen sulfide.” Hydrogen sulfide reacts chemically with oxygen to produce sulfuric acid, which can dissolve whole stadiums of limestone.