Back in 2008 I went on a college geology trip to the American southwest, and our first stop was at Carlsbad Caverns National Park. This park is located in southeast New Mexico along the northeast edge of the Guadalupe Mountains. The mountains rise dramatically above the relatively flat Chihuahuan Desert that surrounds them.
The Guadalupe Mountains began as the Capitan Reef during the Permian Period, roughly 280-250 million years ago. At that time this area was part of a shallow inland sea teeming with marine life like sponges, algae, snails, bivalve mollusks, brachiopods, and trilobites. As they died the shells of some of these organisms collected over time, ultimately forming a reef hundreds of feet thick and hundreds of miles long. Near the end of the Permian the reef died out and it was covered with other sediments like mud and sand, burying it for over 200 million years.
Over the last twenty million years tectonic forces have uplifted this region thousands of feet, leading to erosion and exposure of the Capitan Reef as the Guadalupe Mountains. Made up of dead shelled marine organisms, the mountains are composed almost entirely of limestone. Following uplift, chemical weathering of this limestone began to form the caves now found here.
Most solutional caves are formed when limestone or other soluble rocks are dissolved over time by carbonic acid. Rainwater that permeates the ground combines with atmospheric carbon dioxide to form the acid. The caves at Carlsbad Caverns formed a bit differently. Rainwater percolated down into the limestone where it met hydrogen sulfide-rich water rising from underground petroleum reserves. This resulted in the formation of sulfuric acid, which is much more powerful than carbonic acid. The aggressive dissolution of the limestone created some deep, elaborate caves rich in gypsum (a product of sulfuric acid weathering) and lacking the flowing underground water typical of caves carved by carbonic acid weathering.
The establishment of the beautiful speleothems (cave formations) began even more recently. During the last few million years some of the cave roofs collapsed, allowing atmospheric gasses to enter. Now as water drips from the ceilings, it evaporates and leaves behind tiny amounts of calcite and other minerals from the dissolved rocks.
These minerals accumulate over time and create the detailed speleothems that fill the caverns. Stalactites hang from the ceilings, stalagmites stand up from the floors, and columns ultimately join the two. In addition to these well-known formations, there are also straws, drapes, pearls, and other fascinating features.
Although I’ve been in a number of caves, Carlsbad Caverns is still the most impressive to date. While it lacks the sheer scale of Mammoth Cave National Park, the abundance of speleothems more than compensates.
The photos shown here are the few that turned out during a tour of only one part of the caves. There’s a lot more to see here, and it can only really be appreciated in person.
Although there are many more caves I have to explore in the United States, I highly recommend Carlsbad Caverns as an excellent place to visit. In the near future I plan to visit Big Bend National Park and Guadalupe Mountains National Park in Texas, and plan to revisit Carlsbad Caverns on that trip. It’s good enough not only to see, but to see more than once.