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Roger Weller, geology instructor

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Lechugilla Cave, New Mexico
by Jessica Schaefer
Physical Geology
Fall 2011
       
  

The Unveiling of Lechuguilla Cave

Lechuguilla Cave is located in New Mexico at coordinates 32°10'N , 104°29'W and is part of the Guadalupe Mountain range. Lechuguilla Cave was discovered in 1986 by cavers who dug into a depression that was known to be mined for salpeter long ago near Carlsbad Cavern in New Mexico. Lechuguilla was named for the prickly lechuguilla bushes that cover the ground some 1400 feet above the cave. Lechuguilla Cave is the deepest known limestone cave in the United States with a surveyed length in excess of 185 km. Very few people have been so fortunate to experience Lechuguilla Cave, as it is protected and access to the cave is restricted to scientific caving expeditions. It is not only the very existence of the cave that is so astonishing, but the process as to how Lechuguilla Cave was formed inside the Guadalupe Mountains.

            Description: http://www.pbs.org/wgbh/nova/assets/img/journey-into-lechuguilla-cave/image-02-large.jpg                       
       Lechuguilla lies within this mountain range that was once an ancient coral reef.

                                       Photo credit: © WGBH Educational Foundation

Lechuguilla Cave is home to many wondrous formations, and with over 150 km of cave passages having been explored, we are able to share in the marvelous beauty that scientists have filmed and photographed. The pure white gypsum that now decorates most of the cave comes in a myriad of forms: crystals, flakes, flowers, spikes, cones, and powder. The once limestone dominant mountain is now a gypsum dominant cave. The cave is engulfed by stalagmites, stalactites, and other formations that scientists have named mammillaries, a more exotic form of stalactites.

            Outside of minerals and massive crystal formations, scientists have also discovered and named several lakes: Lake Lechuguilla, Lake Lebarge, and Lake Castrovalva; some of which are at depths in excess of 50 feet deep and 100 feet across.

Description: http://www.pbs.org/wgbh/nova/assets/img/journey-into-lechuguilla-cave/image-05-large.jpg

Stalactites of selenite (a transparent, crystalline form of gypsum)

Photo credit: © WGBH Educational Foundation

Description: http://www.pbs.org/wgbh/nova/assets/img/journey-into-lechuguilla-cave/image-06-large.jpg

Mammillary stalactites named for their mineral nipple appearance

Photo credit: © WGBH Educational Foundation

                                       

Lechuguilla Cave is a member of a rare class of caves that are leached by sulfuric acid solutions versus the more common slow dissolution of limestone by carbonic acid in the water (karstification). In Lechuguilla, the water was more acidic as a result of increased levels of hydrogen sulfide. These increased levels originate from nearby oil bearing sediments. Water and hydrogen sulfide mix to form sulfuric acid which is the component responsible for this magnificent wonder. The more in-depth scientific process is called speleogenesis. Lechuguilla Cave has served as a unique location to researchers in their studies of geology, microbiology, geochemistry, and speleogenesis.

 

Description: http://www.pbs.org/wgbh/nova/assets/img/journey-into-lechuguilla-cave/image-04-large.jpg

Lake Castrovalva

                                                 Photo credit: © WGBH Educational Foundation

Speleology is the scientific study of caves. Speleologists have said that the Carlsbad caves, including Lechuguilla, were formed when Hydrogen Sulfide (H2S) was oxidized into Sulfuric Acid (H2SO4). As the H2SO4 migrates upwards, it mixes with the fresh waters that are in the Capitan reef and fore reef limestones and dolostones. Speleogenesis influenced by H2SO4 produce by-product materials, both primary and secondary, that have been used in the dating of the Carlsbad caves. Speleogenesis is a much faster process than karstification. Below is a list of known primary and secondary speleogenetic byproducts found in Lechuguilla Cave.

Primary speleogenetic byproducts in Lechuguilla Cave

 

Alunite

KAl3(SO4)2(OH)6

Gypsum

CaSO4·2H2O

Hydrated halloysite

Al2Si2O5(OH)4·2H2O

Jarosite

KFe3(SO4)2(OH)6

Natroalunite

NaAl3(SO4)2(OH)6

Rancieite

(CaMn)Mn4O9·3H2O

Sulfur (elemental)

S

Todorokite

(CaMn)Mn5O11·4H2O

Secondary speleogenetic byproducts in Lechuguilla Cave

 

Amorphous silica

SiO2·nH20

Metatyuyamunite

Ca(UO2)2(VO4)2·3H2O

Quartz

SiO2

Tyuyamunite

Ca(UO2)2V2O8·5-8H2O

The information in this table was taken from Victor J. Polyak and Paula Provencio – By-product materials related to H2S-H2SO4-influenced speleogenesis of Carlsbad, Lechuguilla, and other caves of the Guadalupe Mountains.

By discovering the existence of these minerals within the cave, scientists were able to definitively state the way in which the cave was formed as well as the time period in which the cave was formed. Of these minerals, gypsum is the most abundant whereas alunite is the most significant. Gypsum is found in such massive quantities due to peculiarities that affect the speleogenesis, ultimately increasing gypsum solubility, and speeding up the breakdown of limestone into gypsum.  Alunite holds the key to revealing the timing of the speleogenesis that occurred in Lechuguilla Cave.

Description: http://skywalker.cochise.edu/wellerr/mineral/alunite/6alunite150a.jpg

Alunite from Marysvale, Utah

Photo credit: Roger Weller/Cochise College

Alunite is the most significant of minerals because it contains Potassium (K), which creates potential for dating the cave, utilizing the K-Ar or 40Ar/39Ar dating methods. Alunite’s chemical composition is KAl3(SO4)2(OH)6. 40Ar/39Ar dating was used by William C. McIntosh at New Mexico Tech, and the results indicate that H2SO4- speleogenesis took place in Lechuguilla Cave from the late Miocene (23.03 to 5.332 million years ago) to early Pliocene (12-4 Ma). The lack of dripping water in Lechuguilla Cave has preserved these minerals preventing further breakdown and made it possible to learn so much about this secret underground grotto.

                          Description: Photo: Calcite towers in Lechuguilla Cave

Calcite columns stretching up to 50 feet in Lechuguilla Cave

Photo credit: Michael Nichols for National Geographic

       Description: Photo: White ripples of calcite folia in Lechuguilla Cave

Rare Calcite deposits known as folia deep within Lechuguilla Cave

Photo credit: Michael Nichols for National Geographic

       Description: http://giantcrystals.strahlen.org/america/lechu4a.jpg

“Lechuguilla: Jewel of the Underground”

Photo credit: Urs Widmer

 

Works Cited

http://www.nps.gov/cave/naturescie006Ece/lechuguilla_cave.htm

http://www.pbs.org/wgbh/nova/earth/journey-into-lechuguilla-cave.html

http://giantcrystals.strahlen.org/america/lechuguilla.htm

http://www.bbc.co.uk/pressoffice/pressreleases/stories/2006/02_february/01/earth_caves.shtml

http://www.caves.org/pub/journal/JCKS/PDF/V63/v63n1-Polyak.pdf

http://www.caves.org/pub/journal/PDF/V62/v62n2-Northup.pdf

http://www.caves.org/pub/journal/PDF/V62/v62n2-Polyak-Provencio.pdf

http://www.venadelgesso.org/testi/carsismoespeleologia/klimc/klimchouk.htm

http://www.merriam-webster.com/dictionary/speleology

http://science.nationalgeographic.com/science/photos/caves-gallery/#/lechuguilla-cave_1037_600x450.jpg

http://science.nationalgeographic.com/science/photos/caves-gallery/#/calcite-ripples_858_600x450.jpg