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Mysterious Life of Caves

How Caves Form


Caves homepage

Cave-Making Agent: Bacteria

Most limestone caves are dissolved into existence by carbonic acid, a mixture of carbon dioxide and water.

Some, however, are created by a more corrosive acid—one that results from bacteria deep within the Earth, feeding off oil deposits.

illustration: unchanged main diagram

These bacteria, called extremophiles because they live in extreme conditions, expel hydrogen sulfide gas. This gas is carried up by groundwater into the cave.

The hydrogen sulfide mixes with oxygen to form sulfuric acid. The corrosive acid eats away at the limestone rock, leaving behind gypsum.

illustration: cavern

Bacteria also live within some of these pitch-black caves.

Unlike their cousins in the oil deposits, these bacteria feed off the hydrogen sulfide, combining it with oxygen to form even more sulfuric acid. Other types of microbes eat minerals within the rock—sulfur and manganese, for example—accelerating even further the cave-eating process.

illustration: cavern

Lechuguilla Cave in New Mexico, most of whose 100-miles-plus passages have been discovered only since 1986, bore all the signs of being carved out by sulfuric acid, though there was no acid still present within the cave and thus no proof that it was the catalyst. Several years ago, scientists found bacteria and the acid it generated in Mexico's Cueva de Villa Luz (Cave of the Lighted House), still alive, still working on the caves walls.

Choose another way that caves can form.

illustration: larger cavern

Intro | Rainwater | Waves | Lava | Bacteria

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