In June of 2013, I had the opportunity to explore Carlsbad Caverns National Park.  Carlsbad Caverns is vast network of caves within the Guadalupe Mountains on the New Mexico and Texas border.

     These large and deep caves are decorated with spectacular limestone columns, stalactites, and stalagmites.

     Unlike most caves, which are formed by carbonic acid from surface sources, Carlsbad Cavern was dissolved mainly by sulfuric acid created by the oxidation of sulfides. This acid is uncommon in ground water except where hydrogen sulfide gas is available from deep sources or where iron sulfides, such as pyrite, are exposed to weathering.

     The caverns are the hollowed-out remains of a fossilized reef from the Permian Age 250 million years ago.  Once under a shallow inland sea, when the area was uplifted a few million years ago, rainwater seeped into cracks in the reef while hydrogen sulfide gas seeped up from vast underground oil and gas deposits.  There the hydrogen sulfide reacts with oxygen at or near the water table and formed sulfuric acid, which readily dissolved the Permian limestone.

     There are numerous varieties of speleothems that form in the Carlsbad Cavern environment, but carbonate dripstones and flowstones are the most common and voluminous, (pictured above).  Dripstones include perhaps the two most well-known cave formations — stalactites and stalagmites. They form when water drips through the ceilings of caves, gradually building up into stalactites. Sometimes, the calcite water drips to the floor, creating stalagmites. When they fuse together, it is known as a column.  Flowstones are formed in a similar process, but the water drips down walls or other structures in the cave, forming encrustations of calcite. While these are the most common, there are numerous other minerals and structures at Carlsbad Caverns, (pictured below).

     The formations are usually calcite, but there are some other minerals that are found in Carlsbad. Where there’s sulfur in a cave, there’s gypsum.  Large deposits of gypsum, a byproduct of sulfuric acid in contact with limestone, can be found in the hypogenic caves at Carlsbad Caverns.

     There are numerous other formations throughout the park in shapes, sizes, and colors that give the caves an other-wordly quality — some examples include the self-descriptively named soda straws, curtains, popcorn, and cave pearls, (picture below).  The image below shows fantastic formations that line the walls with some particularly good cave popcorn

     Without a doubt, the Big Room is the attraction at Carlsbad Caverns National Park. Pictured below, despite being 300 m underground, this cave is anything but claustrophobic. In fact, this is largest cave room in North America with ceilings up to 100 m high!

     Carlsbad Caverns consist of large, interconnected rooms with highly irregular patterns and profiles.  Nearly all of these caves are inactive today after being abandoned by the water that formed them.  The main chambers of the cave are broad, arched rooms and linear, fissure-like passages whose major trends are controlled by the prominent jointing of the Permian reef-limestone.  In places, the rooms are bordered by intricate zones of sponge-work, where the original pores in the limestone have been enlarged by solution to form an interconnected maze of openings similar to that of Swiss cheese.

     The rooms, fissures and sponge-work are the result of solution in the phreatic zone (below the water table).  Vadose solution features are limited to a few minor rills and drip pockets.  

     In 1898, a 16 year old named Jim White discovered the cave when he was riding his horse through the Chihuahuan Desert and witnessed what looked like a black tornado spewing out of the ground. What turned out to be thousands of bats escaping the cave, led the teenage Jim right to a hole in the middle of the New Mexico desert. In his words “I found myself gazing into the biggest and blackest hole I had ever seen, out of which the bats seemed literally to boil” Naturally, Jim climbed right in.

     Jim White “crept cat-like across a dozen dangerous ledges and past many tremendous openings” seeing amazing geological features such as stalactites and stalagmites, soda straws, flowstone, pools of water, rim-stone dams and a huge area known today as the Bat Cave. At one point Jim’s weak kerosene lamp ran out of fuel and he was plunged into darkness “as though a million tons of black wool descended upon me.” Luckily he had a refill and was able to make his way back out. But this was just the beginning for both Jim and the cave.

     Jim White explored and led tour groups through the caverns, but his trips were not for the fainthearted—they began by lowering the visitors down 52 m in a bucket. 

     Nearby the Carlsbad Caverns, I visited a small corner of Guadalupe Mountains National Park.  This fault-block range has spectacular exposures of an extensive Permian reef complex.  After being buried for millions of years, these reef deposits are now exposed in Guadalupe Mountains National Park (in an uplifted block), in karstic features in Carlsbad Caverns National Park (in a down-faulted block), and to the south in the Glass Mountains and Apache Mountains. 

     Superbly exposed here is a portion of what is termed the “Permian Reef Complex,” which contains one of the largest fossil reefs in the world, the Capitan Reef.