Lechuguilla Cave is, as of February 2012, with 134.6 miles (216.6 km) the seventh-longest explored cave in the world and the deepest in the continental United States (1,604 feet or 489 meters), but it is most famous for its unusual geology, rare formations, and pristine condition.
The cave is named for Agave lechuguilla, a species of plant found near its entrance. Lechuguilla is in Carlsbad Caverns National Park, New Mexico. Access to the cave is limited to approved scientific researchers, survey and exploration teams, and National Park Service management-related trips.
Exploration history 
Lechuguilla Cave was known until 1986 as a small, insignificant historic site in the park's back country. Small amounts of bat guano were mined from the entrance passages for a year under a mining claim filed in 1914. The historic cave contained a 90-foot (27 m) entrance pit known as Misery Hole, which led to 400 feet (122 m) of dry dead-end passages.
The cave was visited infrequently after mining activities ceased. However, in the 1950s, cavers heard wind roaring up from the rubble-choked cave floor. Although there was no obvious route, people concluded that cave passages lay below the rubble. A group of Colorado cavers gained permission from the National Park Service and began digging in 1984. The breakthrough, into large walking passages, occurred on May 26, 1986.
Since 1986, explorers have mapped over 130 miles (210 km) of passages and have pushed the depth of the cave to 1,604 feet (489 m), ranking Lechuguilla as the 7th-longest cave in the world (4th-longest in the United States) and the deepest limestone cave in the country. Cavers, drawn by the caves' pristine condition and rare beauty, come from around the world to explore and map its passages and geology.
In May 2012 a team led by Derek Bristol of Colorado climbed over 410 feet (120 m) into a dome and discovered several new, unexplored passages, pits and large rooms. This new section was named "Oz" and many of its features were named after items from The Wizard of Oz. The discovery included a large room measuring 600 feet (180 m) long, up to 150 feet (46 m) wide and up to 150 feet (46 m) high. It was named "Munchkinland". A pit, named "Kansas Twister", at over 510 feet (160 m) from floor to ceiling, is the deepest pit yet discovered in the park. The ten person exploration team included members from Colorado, South Dakota, New Mexico, California and Arizona. The team spent eight days mapping Oz, adding the largest distance to the survey since 1989, and bringing the total length to 134.6 miles (216.6 km).
Lechuguilla Cave offered more than extreme size. Cavers were greeted by large amounts of gypsum and lemon-yellow sulfur deposits. A large variety of rare speleothems, some of which had never been seen, included 20 feet (6.1 m) gypsum chandeliers, 20 feet (6.1 m) gypsum hairs and beards, 15 feet (4.6 m) soda straws, hydromagnesite balloons, cave pearls, subaqueous helictites, rusticles, U-loops and J-loops. Lechuguilla Cave surpassed its nearby sister, Carlsbad Caverns, in size, depth, and variety of speleothems, though no room has been discovered yet in Lechuguilla Cave that is larger than Carlsbad's Big Room.
Scientific exploration has been conducted. For the first time, a Guadalupe Mountains cave extends deep enough that scientists may study five separate geologic formations from the inside. The profusion of gypsum and sulfur lends support to speleogenesis by sulfuric acid dissolution. The sulfuric acid is believed to be derived from hydrogen sulfide that migrated from nearby oil deposits. Therefore this cavern formed from the bottom up, in contrast to the normal top-down carbonic acid dissolution mechanism of cave formation.
Rare, chemolithoautotrophic bacteria are believed to occur in the cave. These bacteria feed on the sulfur, iron, and manganese minerals and may assist in enlarging the cave and determining the shapes of unusual speleothems. The claim in the BBC documentary series Planet Earth that these bacteria do not derive any energy from the sun is incorrect, as the majority are sulfur-oxidizing bacteria that utilize primarily atmospheric oxygen (derived from sunlight-driven photosynthesis) as an electron acceptor.
Other studies indicate that some microbes may have medicinal qualities that are beneficial to humans.
Lechuguilla Cave lies beneath a park wilderness area. The cave's passages may extend out of the park into adjacent Bureau of Land Management (BLM) land. A major threat to the cave is proposed gas and oil drilling on BLM land. Any leakage of gas or fluids into the cave's passages could kill cave life or cause explosions.
Lechuguilla Cave was shown in the BBC documentary series Planet Earth. The fourth episode, titled "Caves", airing on April 22, 2007, documented scientists and filmmakers exploring Lechuguilla Cave, including the Chandelier Ballroom, which has high-quality crystals. It took the team two years to get permission to film, and local authorities are unlikely to allow another film crew to enter in the foreseeable future.
The Denver Museum of Natural History (now known as the Denver Museum of Nature and Science) filmed one of the first documentaries in the cave, titled Lechuguilla Cave: The Hidden Giant, in 1987, featuring many of the cavers responsible for the breakthrough and initial survey work. The video was broadcast on the Denver PBS station KRMA in 1989 and was available for purchase at the Denver Museum until the early 1990s.
The 1992 National Geographic Society program titled Mysteries Underground was also filmed extensively in Lechuguilla Cave.
- Bob Gulden (February 18, 2012). "Worlds longest caves". Geo2 Committee on Long and Deep Caves. National Speleological Society (NSS). Retrieved February 25, 2012.
- Bob Gulden (February 18, 2012). "USA deepest caves". Geo2 Committee on Long and Deep Caves. NSS. Retrieved February 25, 2012.
- "Carlsbad Caverns National Park: Lechuguilla Cave". NPS. Retrieved 2009-01-22.
- "Deepest pit found in Lechuguilla Cave". Current-Argus. Retrieved 18 June 2012.
- Diana E. Northup, Kathleen H. Lavoie (2001): Geomicrobiology of Caves: A Review, Geomicrobiology Journal, 18:3, 199-222
- Bacteria, fungi and biokarst in Lechuguilla Cave, Carlsbad Caverns National Park, New Mexico K. I. Cunningham, D. E. Northup, R. M. Pollastro, W. G. Wright and E. J. LaRock, Environmental Geology Volume 25, Number 1, 2-8, doi:10.1007/BF01061824
- "Caves". Planet Earth. Season 1. Episode 4. 2007-04-22.
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