How are caves formed?

Water erosion creates most caves found along coastal areas. Waves crashing against the rock over years and years wear down part of the rock, creating a cave. Inland caves are also created by water erosion; groundwater erodes limestone, creating underground passageways and caverns. Lechuguilla Cave, in Carlsbad Caverns National Park, New Mexico, is the deepest cave in the United States. Unlike most caves in which carbon dioxide mixes with rainwater to produce carbonic acid, these caverns were shaped by sulfuric acid. The sulfuric acid was the result of a reaction between oxygen that was dissolved in groundwater and hydrogen sulfide that came from far below the cave’s surface. Since 1984, explorers have mapped 120-plus miles (193-plus kilometers) of passages and recorded the depth of the cave as 1,604 feet (489 meters), ranking Lechuguilla the fifth longest cave in the world. (The longest cave in the world is Kentucky’s Mammoth Cave, which is almost 350 miles [560 kilometers] long!)