by Abellio

Los Angeles, 7 April 2018

Alert readers of my previous posting may have been asking themselves what was the origin of the gypsum strata in the San Andres and Sacramento mountain ranges, which had played such a crucial role in the creation of the White Sands dunes (because, of course, they had not been magically created out of nothing, nor had they been lying there since the birth of the Earth). I’m not sure I can give a categorical answer to this question, but our visit to the nearby Carslbad caverns suggested one possible answer.

A little bit of background is in order here for the uninitiated. Carlsbad caverns constitute a very large underground limestone cave system in the Guadalupe Mountains of New Mexico. This little diagram gives an idea of the extent of the caves. As one can see, it is a series of large chambers connected by passageways.

Videos in the Visitors’ Centre helpfully inform the interested viewer that these chambers were formed by our friend gypsum! Many millions of years ago, as the Guadalupe Mountains were being uplifted, the limestone strata making them up cracked and fissured as the rocks twisted and turned. Rainwater percolated downwards through the cracks until it reached the water table, while hydrogen sulphide percolated upwards, given off by the crude oil and natural gas lying far below (and which we saw being pumped out on our way to the caverns).

When the hydrogen sulphide met the groundwater, it reacted with the oxygen in the water to form sulphur dioxide which then reacted with the water to form sulphuric acid. So the limestone cracks and fissures now found themselves bathing in sulphuric acid. This unforgiving acid attacked the limestone and turned it into calcium sulphate, which is none other than our friend gypsum. The gypsum washed away, leaving fresh limestone to be attacked by the sulphuric acid. And then the cycle repeated itself until the small cracks and fissures had turned into huge caverns. I imagine a similar process created the gypsum strata with which I started this post: hydrogen sulphide bubbling up into a sea above, the sulphuric acid so created attacking coral formations and turning the sea into a vast pool of dissolved gypsum, the sea drying out thereby creating beds of crystallized gypsum. Something along those lines.

Coming back to the Carlsbad caverns, as the uplifting of the Guadalupe Mountains continued the caverns were raised out of the water table and drained of their acid. The caverns would no longer grow. But the rainwater kept percolating down, and in so doing filled the caverns with those formations which make such caves a wonder: the stalagmites and stalactites of course, but also the sheets, the draperies, the ribbons, the flowstones, … Carlsbad caverns have their share of these wonders. But first one has to get to them. The caves have a natural opening at the surface

through which Mexican free-tail bats stream in and out at night

as do cave swallows during the day.

But so do human visitors, who walk down, down, down

into the central chamber of the cave system, the Lunch Room, a huge cavern rather oddly decked out as a cafeteria.

From there, visitors can explore – guided or unguided – other chambers. We chose to take the tour of the King’s Palace, which offered us these views.

This cavern was also home to some strange-looking formations, which I had never seen before. The formations looked somehow gnarled and knotty.

It seems that these proturbances have been formed by convective patterns in the cavern’s air streams gently pushing the drops of water in directions other than down.

I hope I haven’t bored my readers with all this science. I find it fascinating, although I recognize that others may find it tedious or, even worse, that it may bring back bad memories of sitting benumbed in chemistry classes at school. To make it up to them, let me talk about art, or more specifically prehistoric cave art. Of which, unfortunately, there is hardly any at Carlsbad caverns. There is no prehistoric art in the caves themselves. It seems that the Native Americans were afraid of entering the cave, from which they believed their ancestors had originated. There are reports of Native American pictographs around the natural opening, although I didn’t see them and found no photos of them on the web. No matter! I’ll transport ourselves thousands of kilometers eastward to the caves in France and Spain on whose walls our Paleolithic ancestors painted some 40,000 years ago, and I’ll throw in some pictures of the cave art one can find there.

These paintings are very interesting, no doubt about it, but what impresses me even more is that the artists ventured so deep into the earth to paint them. At some point during our tour of the King’s Palace, our guide turned off all the lights. The resulting darkness was absolute. Your eyes never accustomed themselves to the dark as they would outside, allowing your eyes to eventually see something, even if only indistinctly. It was instead unremittingly pitch black, an extremely disagreeable sensation. Of course, our Paleolithic ancestors would not have painted in the dark, they would have taken torches down. But even a torch would have given off precious little light; our guide lit a lantern powered by a candle and such light is faint indeed.

How did our ancestors create such lovely sketches in such a tremulous light? And how did they overcome their fear in going so deep into the inky blackness of these caves? Questions without answers.

Map of Carlsbad caverns:
Oil derrick in New Mexico:
Natural opening:
Bats at natural opening:
Cave swallows at natural opening:
Path down through natural opening:
Main Corridor:
Lunch Room:
King’s Palace-1: my wife’s photo
King’s Palace-2:
King’s Palace-3:
Gnarled, knotty formations: my wife’s photo
Prehistoric art-1:
Prehistoric art-2:
Prehistoric art-3:
Prehistoric art-4:
Candle in a cave: