Geology of Carlsbad Caverns National Park

Carlsbad Caverns National Park is located within the Guadalupe Mountains, a spectacular limestone range which is renowned to have the best preserved Permian aged fossil reef anywhere in the whole wide world. These fossilized ocean creatures show a very detailed and enlightening picture of the coastline of a shallow inland sea, plus the life which called it home some 240 – 280 million years ago. The Capitan Reef was not built by corals like the reefs of today, oh no, this reef was built largely from sponges and algae. There are loads of different marine mammal fossils to be found at Carlsbad Caverns including crinoids, ammonites, nautiloids, snails, bivalves, trilobites and brachiopods. Eventually this coastline formed a limestone layer of rock more than 1,800 feet thick, more than 400 miles wide and between 2 and 3 miles wide. Towards the end of the Permian age, however, the reef had been covered by newer sediments, thousands of feet of them which effectively buried the reef for millions and millions of years.

Over the last 20 million years or so there’s been a lot of activity in the area, faulting and stresses of the earths crust have successfully uplifted the reef sediments to an incredible ten thousand feet (well, almost), then along came the wind, the rain, the snow and old father time eroding the younger sediment until the ancient reef was exposed once more. There really is a unique and amazing opportunity to view the fossil reef on the inside at Carlsbad Caverns National Park, what with all those caves and deep canyons.

Carlsbad Cavern National Park Caves

There are 117 known caves within the national park, some of them being the biggest and the longest caves in the world. They’ve all been created by a rather unusual ingredient, sulfuric acid – which worked aggressively in the dissolution of the rocks.

In most cases limestone caves are created slowly and gradually as surface water flows through the cracks, eventually enlarging passageways and creating caverns and caves. All surface water does contain carbonic acid which is a weak acid and is responsible for the creation of 90% of the limestone caves around the world. These caves are usually extremely wet places with running water, internal lakes, waterfalls and streams. The Carlsbad Caverns National Park caves, however, do not contain any running water – there are no streams, no rivers, no lakes, and no evidence that carbonic acid had a hand in the dissolution of these caves at all . . . hmmm, interesting!

Since the 1970’s geologists have begun to understand that the major player in the dissolution of these caves was sulfuric acid. It’s all down to the hydrogen sulfide from oil deposits within the area plus a whole range of newly discovered microbes which combine with oxygen . . . creating sulfuric acid. I know it’s getting a little technical, but think of the brownie points you’ll get from your nearest and dearest. Anyway, this aggressive dissolution happened at the water table level using the cracks, faults and fractures in the limestone as an escape route. As the Guadalupe Mountains were gradually uplifted, the water table level dropped hence the acid bath began to drain away and leave a whole batch of newly dissolved caves in its wake.

At some point over the last few million years (not sure exactly when), a collapse occurred at the top of the cave, throw in a little surface erosion for good measure and the natural entrance to Carlsbad Caverns appeared, giving access to many underground caves and passageways for the first time. This allowed the air to flow through the caves and the final part of the creation of these mystical caverns – the decorators came in – okay, the geological development of glorious cave decorations – totem poles, rim stone pads, shelves, lily pads, cave pools, stalagmites, flowstone grow from the floor, whilst hanging from the ceiling are awesome sights like stalactites, draperies, soda straws, ribbons and curtains. These are continuing to grow to this very day.

So there you have it, how Carlsbad Caverns came to be in a nutshell, (okay, of course they’re not in a nutshell, but you know what I mean).

Seeing really is believing.